Yankee Siege

2000 Foot Barrier Broken

2009-11-10T17:53:00.008-05:00

Another Punkin Chunkin season has come and gone. I can't believe it's been 6 years of competition for Yankee Siege. I can't believe we pulled off another 1st place! Six straight years of wins, with no losses, its like a dream come true. And to top it off, to break the 2000 foot barrier. I am so proud of all the team members who worked so hard this year so that we could be the first treb in history to break the 2000 foot mark in competition. I would especially like to thank my wife Kathleen for putting up with me and this weird sport. We are the only members of the 2000 foot club, quite an exclusive club! This is one time that its nice to be lonely at the top!

The treb division this year was very impressive with nine machines throwing in excess of a thousand feet. The 2000 foot club will soon be crowded. I was particularly impressed with "new comer" American Chucker with their 1895 foot shot on Sunday 11/7/2009. With only 2200 pounds of counterweight and a ten foot drop that is 35% efficient! Very nice! This is a great machine and a great bunch of guys. Not bad for their first year in competition. They mentioned that they only tested 6 shots before the competition. Image what it will shoot with a little more tuning!!! Good luck!

Its nice to see our old comrades from Pumpkin Hammer and Merlin. Unfortunately, both their machines had breakage problems a short time before competition and could not live up to their full potential. Both of these machines are beautiful examples of ingenuity and efficiency and are easily capable of a 2000 foot plus throw! When these machines are fully functional, watch out!

Yankee Siege's goal has always been to break the 2000 foot barrier. I told my wife back in 2004, that once we broke 2000 feet we would retire from competition. Be careful what you wish for!!! I didn't think we would ever reach that goal or not quite this quickly at least.

The 2000 foot goal has presented several problems for Yankee Siege. The biggest problem is space in our test site at the farm stand. We have run out of space. We are now capable of hitting 4 houses with several throws this year in excess of 2300 feet. It is making me very nervous that we will do harm to an adjacent property.

The second problem with continued competition is cost. It costs Yankee Siege $15,000.00 to compete every year in Delaware. We are looking for sponsors to cover some of the costs. Maybe we could just bring in the machine to throw 100 pound pumpkins as a crowd pleaser and not compete. Maybe we should retire. It's been a great run for the past 6 years with many fantastic memories. It will be hard to "top" this year with all the media attention and the 2000 foot throw. It might be best to leave while you are at the top of your game. To be continued.

Steve Seigars, YS

Yankee Siege Update November 7, 2009 from Punkin Chunkin Delaware U.S.A.

2009-11-07T23:46:00.003-05:00

Just a quick update!
Yankee Siege on Friday November 6, 2009 had a throw of 1298 feet.
Yankee Siege on Saturday November 7, 2009 had a world record throw of 2039 feet.
Correction, 11/7/2009 throw was 2034 feet.
One day to go to defend our 2008 World Punkin Chunkin Championship record!

Wish us luck,

Steve Seigars, YS

Yankee Siege Tune-Up October 24, 2009

2009-10-24T21:09:00.009-04:00

We are making a concentrated effort to tune and tweak Yankee Siege with the new throwing arm. We have decided to leave the counterweight alone with a fixed amount of weight (12,000 pounds).

The pumpkin will also remain a fixed weight of ten pounds.

That leaves us with only two parameters to adjust (sling length and pin angle). We will try to tune the machine to time the release to coincide with the maximum velocity of the machine (not necessarily to the ideal 45 degree angle). As we all know, distance is proportional to the velocity squared. So it is much more important to time your machine to the maximum velocity and not be obsessed with the ideal 45 degree angle. Most machines will not have a coincident 45 degree release angle and maximum velocity.

The key, in my opinion, is to vary the pin angle and sling length in combination to get the maximum velocity and 45 degree angle to coincide. This "magic combination" may not be possible with every machine. Different geometries and masses in a traditional treb versus a FAT or a whipper or Merlin's ski jump will dictate when the maximum velocities are reached in the cycle.

It must be remembered that given two equal release velocities, any angle of release between 30 degrees to 60 degrees will give 85 percent of the ideal 45 degree maximum distance. You are better off tuning to maximum velocity. Small increases in release velocity will yield exponential increases in the distance thrown. Distance will increase by the velocity squared. A ten percent increase in velocity will yield a 21 percent increase in distance thrown.

Yankee Siege has setup sling lengths of 24 ' 6 " through 30 ' in 6 " increments. We also have 4 pins at various angles. We will only throw 10 pound pumpkins. With 4 pins and 12 sling lengths that makes 48 possible combinations. Do we have enough time to tune-in the machine? That will require 48 ten pound round pumpkins, no wind, good weather etc! Can we shorten the process? If we shorten the process are we going to miss just the right combination? (Note: most simulators will show 2 peaks of near maximum velocity with a steep valley in between. There are probably many more combinations that will probably work. There are an infinite number of combinations given small enough increments of pin angle and sling length).

We may run into some interference problems with the frame when we use a 30 ' sling. (Yankee Siege is an underslung trebuchet, withdrawing the projectile from under the frame). The sling and/or the pumpkin will come dangerously close to the frame. This could spell disaster if the sling should "fetch-up" on the frame, possible breaking the pumpkin or breaking the arm. (Note: we will be bringing 2 throwing arms to the competition, just in case). This is a basic design flaw of Yankee Siege.

Timing has become a more precise issue with a new throwing arm. It is faster than the previous throwing arms, making correct timing much more critical. A tenth of a second too "early" or too "late" will lead to significant decreases in distances thrown. We may have to accept a little greater percentage variation from throw to throw.

A Note on Sling Length

We want the longest sling length possible and still have time for the sling "to come around" and release at the proper time. A long sling will further multiply the speed of the accelerating counterweight by increasing the effective radius of the long end of the throwing arm. A longer sling will "steal" more of the angular momentum from the throwing arm, causing the throwing arm to slow and transfer more energy from the counterweight to the throwing arm to the projectile. A projectile that is allowed to move away from the axle can significantly increase the moment of inertia of the throwing arm/projectile combination. This is analogous to a spinning skater throwing out her arms and slowing her rate of spin. In a very efficient machine, the throwing arm will almost come to a "halt" at the time of release of the projectile.

Yankee Siege hopes that by increasing the sling length in six inch increments, we will find a length that will accelerate at just the right angular velocity to be close to a 45 degree angle when the counterweight "stalls" as it becomes collinear with the throwing arm.

Two Thousand Foot Holy Grail!!!

Can 2000 ' be broken for a trebuchet? Can 2500 ' be broken? Will the weather cooperate? Could all 3 of the "big three trebs" (Yankee Siege, Pumpkin Hammer & Merlin) break 2000 '? A throw of 2000 ' may only garner 3rd place! Will an unknown machine come and beat us all? That's the excitement of Punkin Chunkin. To get a good throw everything "has to go right"! To have a bad throw only one thing has to go wrong! How does one "make it happen"? How does a team make everything go right? How does a team prevent a mistake or breakage of the machine? What part does luck play? Do you make your own luck through practice, vigilance, hard work and experience?

We only have a little bit more than a week left. Yankee Siege sincerely wishes all the other trebs in the division the best of luck in the 24th Annual Punkin Chunkin competition. Hope the weather cooperates and the 2000 foot mark is blown away!

Steve Seigars, YS

P.S. A Note of Finding Good Pumpkins to Throw!

Today was a rainy Saturday. We spent the whole day looking for just the right pumpkin. Luminas are very scarce this year. Trying to find just the right weight and shaped pumpkin that is free of rot or bruising is not an easy task. Luminas are almost impossible to find. There are, however, three other choices:

1. The Cuban pumpkin called the La Estrella. This is a smooth, spherical, dense pumpkin. It is sometimes available in specialty produce stores catering to Cuban, Portuguese or Brazilian groups.

2. The White Buttercup. This is similar in size, shape and density to the La Estrella. This is not the same thing as a butter cup squash.

3. The Traditional Orange Pumpkin (many different varieties). Although not as dense as the first two choices, it may be the only one available.

We will be looking for Buttercup and La Estrella at the Chelsea Wholesale Produce Market Terminal in Boston.

P.S.S. Yankee Siege will be bringing different weight pumpkins for trading with other teams. Yankee Siege needs ten pounders, we will trade some of our lower weight pumpkins for ten pounders.

See the Yankee Siege in action, click the links below!

Yankee Siege YouTube video 1
Yankee Siege YouTube video 2
Yankee Siege YouTube video 3
Yankee Siege YouTube video 4

Yankee Siege Update October 20, 2009

2009-10-24T20:38:00.002-04:00

Yankee Siege is back in operation! The throwing arm axle bearings have been replaced with new and beefier bearings. We were able to get new bearings from Bearings-Specialty.com in Nashua, NH. The new bearings were not the same dimensions as the old bearings and required some reworking of the supports and the throwing arm. Thanks to team members and ace mechanics Chuck Willard and Ken Holland, they made short work of the job and were able to get Yankee Siege fixed without missing a single weekend of demos at the farmstand. Also, thanks to my wife Kathleen for not murdering me after picking up the bearings and finding out the cost.

The four new pillow-block bearings are performing flawlessly and are holding the axle firmly in position with no slipping or axial movement of the towers. We now have six massive bearings supporting the 4" diameter solid steel axle!

Yankee Siege Destroys Main Axle Bearings - October 5, 2009

2009-10-05T21:04:00.002-04:00

Just finished a weekend of throwing. Saturday was raining and no throws. Sunday was a beautiful fall day in the 60's and perfectly calm. Several shots exceeded the 2000 foot range, but some shots released very late and were very low. We don't know what exactly is causing the late release (we did throw some rather light pumpkins in the 8 pound range and that may account for the late release but even some of the ten pound pumpkins would release somewhat late).

Today (Monday) we entertained a high school physics class. This was a small class with very attentive students. It's nice to see a well behaved class with students that appear to be interested in physics and math. I'm afraid I may have talked too long. I have a tendency to be long winded and perhaps too technical when it comes to trebuchets. I get very excited. Sometimes it's hard to talk to a class that has just been introduced to projectile motion and not be too technical. I could talk for days. They had to shut me up and get on with the demo or we would have run out of time.

Bearing Failure

Just before the class, Chuck and I went to inspect the main axle bearings for the throwing arm. We have been noticing that the bearings on one side had appeared to be loosening and causing one of the towers to move inward, causing a binding of the throwing arm against the frame. Upon closer inspection we found that two of the four bearings had cracked housings. These bearings are forty year old Dodge pillow block bearings obtained from a junk yard. We suspect that the new throwing arm is the culprit. The new throwing arm is so light and has such a low moment of inertia, that the counterweight literally "falls" for 12 feet and slams to a near halt at the end of its travel. This action of the counterweight causes a significant increase in the reaction force on the axle leading to failure of the bearing. (We don't know exactly when this cracking occurred, it may have started last year and went unnoticed until this year with a new throwing arm). There is about a 3/16 th's inch wide crack on the lower part of the bearing housing.

Now we have to figure out how to solve the stress on the bearings. We have decided to put six bearings on the axle (we now have 4 bearings). We will also move the two inner bearings on each side as close to the throwing arm as possible (the inner bearings take most of the load).

This is just another example of unanticipated stresses with a change in the configuration of the machine. A lighter throwing arm can lead to vast increases in the reaction force on the axle. Yankee Siege has a four inch solid steel axle through the throwing arm and turned down to 3 and 7/16 th's inches in the bearings

We have ordered four new bearings that will be here Thursday. Changing the bearings will not be an easy task. It will require removing the new throwing arm, removing the counterweight and stub throwing arm, beating off the old bearings and then reassembling. Hopefully we will be ready for Saturday's demos. Actually, the hardest part of the whole project is telling my wife how much I just spent on the new bearings! Wish me luck!

Steve Seigars, YS

Yankee Siege Update - September 27, 2009

2009-10-05T20:22:00.004-04:00

This spring and summer have been a very busy time for Yankee Siege. I haven't had the time to update our progress. We have been visited by four TV shows. Time Warp (Discovery Channel), Lock and Load (History Channel), All Jacked Up (Country Music TV), and The Science Channel following teams to Punkin Chunkin (more about the shows later).

This year's Punkin Chunkin will almost surely see the two thousand foot barrier broken by a trebuchet. Yankee Siege's goal is to break the 2500 foot barrier! We have fabbed a brand new throwing arm and unveiled it for the first time in front of the cameras for Discovery Channel. The arm is very light and fast! We have reduce the weight of the arm to a mere 600 pounds, down from our previous arm of 800 pounds, down from the original arm of 1200 pounds. Not only have we reduce the weight but we have moved some of the mass of the throwing arm considerably closer to the axle, with the effect of significantly lowering its moment of inertia (resistance to a change in rotational velocity). We are still running 12,000 pounds in the counterweight (94,000 foot-pounds of torque, max). We have only done two throws at the time of this posting. I don't know if the arm can take the stress. If the arm holds up, we could potentially break 2500 feet this year. The cable stayed throwing arm has remained straight as an arrow with these first two throws.

We are unable to accurately measure the distance of the throw. At the 1700 to 1800 foot range the pumpkin disappears into some pine trees on the far side of a ten acre wetland. We can only estimate how far into the pines the pumpkin has flown. The first two throws were very far. They were also very low. Almost a line drive. They left the machine at tremendous speed. We will have to adjust the pin angle or sling length to get a higher path. The second throw appeared to rise about halfway through its flight and just kept climbing and didn't reach a peak till somewhere around the 1500 mark.

The extremely low trajectory would seem to indicate that the throwing arm is rotating significantly faster (higher angular velocity) than our previous throwing arm (the throwing arm is able to "get ahead" of the sling causing the sling to release a little later (similar to the effect of adding more counterweight).

We will be doing public demos at the farm stand for the next five weekends. These demos serve as our practice sessions for Punkin Chunkin.

P.S. Lumina pumpkins are very hard to find in New England, we had a very wet and cold June and July. We will have to practice with orange pumpkins. Does anyone have a souce for Lumina's? If you have a source please e-mail us, Thanks.

P.S.S. A special note to Merlin and Pumpkin Hammer, Good Luck in your practice sessions, stay safe and hope nothing breaks. See you in November.

Steve Seigars, YS

Reflections on 2008 Punkin Chunkin!

2008-11-15T12:49:00.006-05:00

This year's Punkin Chunkin, once again, proved to be a very exciting event. Weather conditions were very favorable for setting new world records. Winds were calm and temps were mild, making for very pleasant surroundings. Good weather and good people make for good times.

Now is the time for thanks and reflection of another season gone by. Thanks that nobody got hurt, thanks to good neighbors, thanks to good sportsmanship, thanks to charity, thanks to all those good people that had a hand in putting on and participating in such an event. Thanks to all my team members who worked so hard over this past year to help set a new world record. Thanks to my wife (aka, Trebuchet Widow) who puts up with this odd hobby. Yankee Siege would not survive, if not for her.

Winter and spring are a time for reflection and a time to recharge the batteries (six weeks of public demos at the farm stand can be quite draining, mentally. One is always a little on edge, concerned that something will break or an errant pumpkin will land somewhere it shouldn't). It's nice to have some "free" time to read about physics and plan for the next season.

It never ceases to amaze me the good sportsmanship I have seen at Punkin Chunkin. Teams are so willing to help out one another, to repair a broken machine, to give suggestions as how to improve performance or to just give encouragement.

What is encouragement? Think about the word for a minute. What does it mean?
Encouragement-TO GIVE COURAGE. To give the courage to not be afraid to try. To give courage to not be afraid to fail. Failure is difficult for everyone. It's very difficult for anyone to see their machine fail, especially in front of a crowd. But fail all of us must. Failure makes success all the more sweet. We should expect failure. Failure is good, as long as we don't give up. We should be encouraged by failure. Failure is how we find out what doesn't work. Failure is a path to learning. Failure builds character and can either break you or make you dig deep into your inner being and find a strength you didn't know existed.

In talking about encouragement, I have to share with the rest of the world one of the most touching moments I have witnessed at Punkin Chunkin. Matt (I don't know his last name) the captain of Medieval Postal Service had just finished throwing with his machine (floating axle trebuchet). This is a very well designed FAT. Matt had the courage to compete this year and did exceptionally well as a first time competitor and finished in 5th place. He is a mechanical engineering student and he is obviously quite bright and has a great attitude. He is one of those people you meet and instantly you know that this "kid" is "going places". He has a very positive outlook and is very open. On the last throw, his throwing arm jumped past the stops on the slider and ended up in a heap in front of the machine. Matt handled the breakage in stride and with grace and you could see the wheels turning in his mind as to how to solve the problem in the future. Matt, I think, was a bit disappointed and perhaps needed some encouragement at that moment. Rich Foley (team Pumpkin Hammer) then did something that I will never forget. He calmly went over to Matt and congratulated him for his success and "encouraged" him, saying to him that designs always have to be changed. Flaws and weaknesses in design always show up and this was a normal process that Pumpkin Hammer and other teams have to work through. Rich acted very paternally towards Matt, giving encouragement and congratulations and reassurance. Encouragement from a Punkin Chunkin veteran must have meant a lot.

Rich Foley and the whole Pumpkin Hammer team know very well that if you keep on trying, keep on redesigning, keep on failing, keep on succeeding, that sooner or later they will the winners (or perhaps Matt will beat us all).

This is an example of great sportsmanship. It's not so important if you win or lose, it's how you play the game. Don't get me wrong, Yankee Siege, wants to win but we realize that we have been very lucky the past five years. Winning is only a temporary condition. The friendship and camaraderie will last longer and are far more important.

My hat is off to Rich Foley and the whole Pumpkin Hammer team for the leadership that they have shown. Great leaders don't only think about themselves but the whole division. The trebuchet scoreboard was a great idea (except for Friday if your in last place). I know that one day that Pumpkin Hammer will be on the top of the scoreboard. But right now they are already in first place in leadership.

THE BAR HAS BEEN RAISED!

Who would have thought a year ago that a 1589 foot throw would only get you third place? Both Pumpkin Hammer and Merlin have made great improvements in their machines this year. Both have doubled the distance of their last year throws. If this improvement continues, Yankee Siege will end up in third place or worse next year. Medieval Postal Service is the new "kid" on the block and may surprise us all.

I can't help but notice a parallel with giant pumpkin growers. It was just a few years ago that they broke 1000 lbs for the biggest pumpkin. Now 1000 lbs is only a mediocre size. The largest pumpkin is now over 1600 lbs. How things change. Records were meant to be broken. Competition focuses the mind and leads to innovative designs such as Merlin.

It's interesting to see what happens after the last throw of the season. The mind starts to think, what change can I make to the machine to make it throw a greater distance? How do I keep first place? How do I stay ahead of the competition. How do I beat Yankee Siege? What will Yankee Siege do? Will they sit on their laurels? How much will modifications cost? Will my machine be able to take additional stress? Will I have to totally redesign? Can I do just a little more to keep ahead of the competition. How much more can the competition improve? How radical do I want to be? Do I need to know more about the physics of a treb? Do I need to know more about materials? Where does it end? How much time do I spend? How bad do I want it? Is it worth it? Do I try something totally off the wall? Will I have a "EUREKA" moment!

Winter is a time for learning, reflection, and most of all planning. Most people don't realize that to be one of the top three competitors requires thousands of hours of work every year. You can't expect to practice a week before the competition and win. All machines require maintenance and modifications to stay competitive! I can only image how many hours Chris Gerow has into Merlin. It's a good thing he's retired, it's a full time job.

I hear through the grapevine that Rich Foley, team Pumpkin Hammer is going to retire soon (not from Punkin Chunkin but from his real job). That will give him more time to think and play (not a good thing for Yankee Siege, 1700 feet is too close, Great Job).

The Yankee Siege team has been batting around different ideas for modification for next year. We really want to break the 2000 foot barrier. If conditions are favorable the 2000 foot barrier will probably be broken this coming year by one of the big three or somebody else- I don't want to forget about Trebarbaric with their 1866 foot shot in 2007. I wish they could bring their machine East. Image the big four all in a row! Wes Frank, Trebarbaric may be building a more portable machine that can travel to Punkin Chunkin.

Enough said! Hope everybody's winter planning goes well, stay in touch.

Remember- Gravity is the most far reaching force in the Universe and keeps us all grounded!

Steve Seigars, YS

P.S. I will be posting monthly updates on our new plans.

P.S.S. A special thanks to John Huber and Hypertension for their help in donating a hydraulic hose that was torn in practice.

P.S.S.S. A special thank you to BSA Troop 672 for pulling the trigger on our first world record breaking throw of the 2008 competition. To see BSA Troop 672 slide show of this world record throw click here Punkin Chunkin World Record Slide show via Boy Scout Troop 672 from Severn, MD.

P.S.S.S.S. Also, another special thank you must go out to team Sister Slinger and company for pulling our 1st place and final world record throw on Sunday of the 2008 competition.

Yankee Siege Wins Trebuchet Division for 2008 at the Punkin Chunk in Bridgeville, Delaware U.S.A.

2008-11-02T20:43:00.012-05:00

Results of 3 day World Championship Punkin Chunkin Competition.

Yankee Siege results;

Friday 10/31/08 - 0 - Pumpkin Pie, pumpkin fell out of the sling.

During our free throw we tore out a hydraulic hose from hydraulic motor after the whole machine fell off our planks. We are in last place, some of the smaller trebs were bragging that they were beating Yankee Siege!

1st Place - Pumpkin Hammer - 1596.
2nd Place - Merlin - 1589.

Saturday 11/01/08 - New World Record throw - 1894 feet!

We made the decision to eliminate our new trough after another pumpkin fell out of the sling during our practice throws in the A.M. before competition. We feel that the pumpkin is contacting one edge of the trough and spinning out of the pouch!

Merlin bent their throwing arm and had to replace it with a spare arm that they brought with them.

Pumpkin Hammer added an undisclosed amount of weight to their counterweight. It looks like it helped.

2nd Place - Pumpkin Hammer - 1640
3rd Place - Merlin - 1564

Sunday 11/02/08 - New World Record throw - 1897 feet!

The 2 previous days had a slight headwind but today we had a strong tailwind in the A.M. that slightly calmed down by the time we fired in the afternoon.

2nd Place - Pumpkin Hammer (Welcome to the 1700 foot club) - 1700 feet!
3rd Place - Merlin (Highest shot of the trebuchet class) - 1260 feet!

Steve Seigars, YS

PS We promised the Trebuchet Widow (Kathy Seigars) that if we reached 2000 feet we would retire from competition!
See you next year at the World Championship Punkin Chunkin Competition.

2008 Trip to Punkin Chunkin!

2008-10-28T18:43:00.012-04:00

It is now 6:45PM on Tuesday 10/28/08, do you know where your tractor-trailor carrying your trebuchet is?

Yes, it's in New York state somewhere broken down (broken alternator belt)!
Trying to find a replacement at AutoZone!!!

Do you know how dry your field is at Punkin Chunkin?

Yes, ours is very wet and they do not know if we can go onto the site tomorrow at 10:30AM when the crane arrives (First State Crane Service)!

Today, Tuesday, has been very windy, following a very substantial amount of rain on Monday night and early Tuesday AM. Hopefully the wind will help to dry up the site so we can setup on Wednesday! Pray for no rain, how often do you hear a farmer saying that!

News Alert!!! Tuesday 10/28/08 7:18PM - Our tractor trailer carrying trebuchet is now back on the road and heading for Bridgeville, DE!

Note to our Yankee Farmer Customers, Thank you for our most successful season at the farm stand! Without you we could not attend the annual Punkin Chunkin competition in Bridgeville, DE. Hopefully we will bring back a trophy to Greenfield, NH.

Weekend of October 18, 19 & 20, 2008 --- Strong Throws, Even with a Headwind!

2008-10-20T21:38:00.008-04:00

We continued to throw with 11,500 pounds of counterweight. Saturday was breezy and in the mid-50's with a steady 10 to 20 mile per hour headwind for most of the day. As late afternoon approached, the wind died down with a consequence of a significant increase in distance.

We added 500 pounds of counterweight on Sunday morning to bring the total counterweight up to 12,000 pounds. There was a 10 mile per hour headwind but the extra weight seemed to over power the wind. We had fairly consistent throws, with one throw at the 2100 foot mark after changing to a 24 foot sling instead of our standard 25 foot sling.

On Monday we had four schools visit our site. These were high school physics and engineering classes, as well as, some grade school students. Winds were very calm but temps were only in the high 40's. We tried a slightly longer sling (26 feet) to see how the machine would react. The throws were very good, with one shot around 1950 feet but very high.

Results of the 19 throws October 18, 19 & 20, 2008

Note: We added 500 pounds of counterweight (Sunday) for a total of 12,000 pounds.

Saturday October 18, 2008

Throw One - 1650 feet
Throw Two - 1400 feet - low trajectory
Throw Three - 1800 feet - high trajectory
Throw Four - 1400 feet
Throw Five - 1800 feet - good height
Throw Six - 1800 feet - good height
Throw Seven - 1800 feet -good height and calm wind

Sunday October 19, 2008

Throw One - 1900 feet - good height
Throw Two - 2000 feet - good height 15 mile an hour headwind
Throw Three - 1400 feet - low trajectory
Throw Four - 2100 feet - good height 10 to 15 mile an hour headwind and change to 24 foot sling
Throw Five - 1650 feet - slightly low trajectory
Throw Six - 1800 feet - good height
Throw Seven - 1700 feet - high hard left
Throw Eight - 2000 feet - slightly low

Monday October 20, 2008

Note: Changed to 26 foot sling.

Throw One - 1850 feet
Throw Two - 1850 feet - good height
Throw Three - 1950 feet - very, very high
Throw Four - 1450 feet - slight pie

PS This will be the last posting of throws before the competition. We will be practicing next weekend but we won't be posting results because we will be dismantling the machine starting on Sunday night and Monday day and that will consume all our time. The logistics of transporting a 52,000 pound machine and associated support on four separate vehicles can be mind numbing. (I have nightmares about forgetting some critical part).

I wish every team the best of luck in their practice sessions. I hope everything goes well and safe and nothing breaks. This year promises to be quite competitive, now that Pumpkin Hammer and Merlin have had a full year to tweak and tune their new machines. Both these teams have designed very sophisticated and efficient machines. Their efficiency far surpasses Yankee Siege. They are smart machines, finesse machines. Yankee Siege is just brute force. Yankee Siege is probably the least efficient machine in the whole competition (dumb machine). Any one of these three machines could win, or maybe some unknown machine will come along. Win or lose, this year will be exciting!

Steve Seigars, YS

Weekend of October 11, 12 & 13, 2008 --- Yankee Siege Breaks 2200 foot barrier!

2008-10-13T21:43:00.003-04:00

The last of sixteen throws of the weekend turned out to be a whopper! With over 16 seconds of flight time, the orange pumpkin flew on a high trajectory and just kept on sailing upward before finally descending to earth after traveling over 2200 feet. We measure our distances from an observation tower located 1200 feet from the treb. The forward observer uses a range finder to measure how far the impact is from the tower and then adds 1200 feet to the total distance.

Several thousand onlookers witnessed Yankee Siege throw throughout the weekend. Weather was sunny and in the high sixties. It was almost a perfect weekend. We had one errant throw that came dangerously close to our nearest neighbor, hitting a tree and raining down pumpkin guts. Luckily, we have great neighbors who are very understanding and we promptly repositioned the treb.

We took seven more throws on Monday with some interesting results. We wanted to see what would happen if we put more slack in the sling. We wondered if more slack would give us more consistent distances. We suspect that the elastic recoil of the throwing arm may be producing a harmonic in the sling, leading to inconsistencies in the timing of release. We tried 12 inches of slack in a 25 foot sling. There were no very short throws. All throws were 1600 feet or above. The slack seems to work (we need more testing to verify).

Results of the 23 throws October 11, 12 & 13, 2008

Note: We added 500 pounds of counterweight (Sunday) for a total of 11,500 pounds.
Note: All pumpkins are orange and used a straighter release pin.

Saturday October 11, 2008

Throw One - 1200 feet - low trajectory
Throw Two - 1300 feet - low trajectory
Throw Three - 1400 feet - low trajectory
Throw Four - 1700 feet - change to straighter pin
Throw Five - 1500 feet
Throw Six - 1700 feet
Throw Seven - 1700 feet
Throw Eight - 1650 feet

Sunday October 12, 2008

Throw One - 1800 feet - good height
Throw Two - 1850 feet
Throw Three - pumpkin fell out of sling
Throw Four - 1650 feet - hard left
Throw Five - 1450 feet - low trajectory
Throw Six - 1600 feet
Throw Seven - 2000 feet - good height
Throw Eight - 2200 feet - in the stratosphere!!!

Monday October 13, 2008

Note: Put one foot of slack in the sling.

Throw One - 1650 feet - slightly low trajectory
Throw Two - 1850 feet - good height
Throw Three - 2100 feet - great height, long flight time
Throw Four - 1900 feet - slightly lower
Throw Five - 1700 feet
Throw Six - 1600 feet - tried underweight Lumina pumpkin
Throw Seven - 1850 feet - good height

PS Next weekend (weather permitting) we will try varying sling length and adding more weight to the counterweight.

Steve Seigars, YS

Sun Returns to Greenfield, NH on the weekend of October 4 & 5, 2008

2008-10-05T21:39:00.003-04:00

Sun was back shining on Yankee Siege this weekend. Temperatures were in the mid 60's, winds were calm and we seemed to have overcome some of our engineering problems of the previous weekend.

We tried out some new items this weekend. First, we tried out a new 10 inch steel trough. We fabbed it by cutting a 10 inch diameter steel pipe into equal halves with a metal-cutting "skill saw". This saw looks and cuts exactly like a wood cutting saw. It leaves a very smooth cut with very little cleanup.

Next we tried to cure our problem of the pumpkin falling out of the pouch. Apparently, what is happening, is that the throwing arm is elastically recoiling when the trigger is released. This is followed by a rebound in the opposite direction, causing a momentary slacking of the sling and a subsequent rolling of the pumpkin out of the sling. We have solved the problem by putting about six inches of slack into the sling and allowing the recoil of the throwing arm to occur before the pumpkin moves down the trough. (Our high speed camera shows the sling actually becoming slack as the throwing arm rebounds).

We threw fourteen pumpkins this weekend with the following results:

Saturday 10/4/08 10,300 pounds counterweight.

Throw One - 1550 feet - slightly low trajectory
Throw Two - 1400 feet - low trajectory
Throw Three - rolled out of sling - didn't put any slack in the sling
Throw Four - 1700 feet - broke 3/16 inch cable stay
Throw Five - 1600 feet
Throw Six - 1500 feet
Throw Seven - 1800 feet - good height
Throw Eight - 1700 feet

Sunday 10/5/08 Added 700 pounds of rail road track to counterweight. Counterweight now 11,000 pounds.

Throw One - 1800 feet - good height, broke cable, bend aluminum extension.
Throw Two - 1900 feet - changed to carbon fiber extension and 1/4 inch cable.
Throw Three - 2000 + feet - good height
Throw Four - 1700 feet - slightly low
Throw Five - 1200 feet - pied into two pieces - cable stay strut slightly bent.
Throw Six - 1750 feet - good height.

Next week we will try adding more weight and trying different pin angles and sling length.

PS All throws were done with orange pumpkins no Lumina pumpkins.

Steve Seigars YS

Rainy Day in New Hampshire September 29, 2008

2008-09-29T21:05:00.003-04:00

Our second weekend of public trebuchet demos was a washout, in more ways than one!

Saturday was totally rained out by Hurricane Kyle. We tried to salvage part of the weekend (Sunday), and managed to get off six throws between rain showers. This was absolutely, positively the worst weekend ever for Yankee Siege! We couldn't do anything right. I hate to even post the results, but I have promised to post all results (good or bad) after each weekend of practice.
Of the six throws, four actually fell out of the sling. One went 1200 feet (a line drive), and one mediocre throw went 1650 feet.

We have been practicing with our eight foot aluminum cable-stayed extension and our new steel based arm with 10,300 pounds of counterweight. The new steel arm appears to flex a little more than our old throwing arm. Upon release of the trigger, the throwing arm springs back suddenly, creating a "hop" of the pumpkin and subsequent rolling out of the side of the pouch. (Yankee Siege has never used a trough). We hope that by using a trough we can cure the problem. Next weekend we will be practicing with a trough and our cable-stayed carbon fiber extension. Hopefully no more rainy days!

Steve Seigars, YS

Late September 2008

2008-09-20T20:26:00.002-04:00

It's been a very busy summer at the farm stand. We grow about 9 acres of pumpkins and that has consumed a good portion of my time and as a result I have neglected the Yankee Siege web site. P.S. I have had no luck in growing Lumina pumpkins. I hope all your practice sessions are going well!

Yankee Siege's new steel throwing arm has been completed and tested. Many thanks to American Steel Erectors, and to Dave Webb the welder. It weighs in at about 700 lbs., a savings of over 400 lbs. over the old throwing arm. This throwing arm will require much less torque to rotate (lower moment of inertia). American Builder (Comcast) came up to the site September 8th to film the unveiling of the new throwing arm. Things fit perfectly, with the throwing arm neatly nestling into the trigger with no interference. They (American Builder) will be following us to Punkin Chunkin to see how the new carbon fiber extension performs.

We test fired the new throwing arm with an 8 foot aluminum extension and an empty counterweight box (8000 lbs.). We also tested it with the 9 foot carbon fiber extension. Things went well with 8000 lbs. We added 1350 lbs. to give us 9350 lbs of counterweight. The furthest throws were in the 1700 foot range.

We did note a difference in motion of the machine. The usual fore/aft movement of the machine was severely restricted. We have added crushed stone under the wheels to help with the footing of the machine (on wet days the wheels sink into the mud). The shifting of the crushed stone appear to inhibit the fore/aft movement of the machine with a consequence of a significant reduction of distance. We have now added sand to the stone to try to stabilize it from shifting. This appears to have worked.

On September 14th we increased the counterweight to 11,000 lbs. This is when weaknesses in the design started to show up! The design of the throwing arm was made on one assumption. We (or more correctly I, I like to spread the blame when something goes wrong) assumed that the maximum peak G forces on the pumpkin would not exceed 40 G's. That would give a force of 400 lbs with a 10 lb pumpkin. Four hundred pounds at the end of the cantilever would translate into a bending moment of 400 lbs. times the distance from the end. This is an easy calculation to make and the design and area moment of inertia of the extension was based on that assumption. We all know what can happen when we assume! What I thought to be a very conservative assumption turned out to be very wrong. We have severely underestimated the forces. The new throwing arm is producing G forces in excess of 60 G's. This is good news and bad news. The good news is that the new steel base is accelerating very quickly with less counterweight. The bad news is that the carbon fiber and aluminum extensions can not take the load. The carbon fiber has broken and the aluminum extension has bent!

At the time of this posting a new beefier carbon fiber extension has been fabbed on the assumption of 80 G's of force. NIM-COR company of Nashua, NH has fabbed the newest carbon fiber extension. It is a high modulus (22 million pounds per square inch fiber) with a tensile strength of 140,000 p.s.i. with a 2.75 inch outside diameter and a 2.25 inch inside diameter. It should be able to withstand 1645 lbs. at the tip. The engineer at NIM-COR was nice enough to give us a tour the carbon fiber manufacturing plant. It was fascinating to see the carbon fiber filament winding machine wrap the carbon fiber around a rotating mandrel. A computer controls the R.P.M. of the mandrel and the axial movement of the carbon fiber carriage. The fibers are first feed through an epoxy bath and then onto the mandrel. Excess epoxy drips off, leaving a high fiber to resin ratio. Next, the mandrel is hoisted into the oven to cure the epoxy.

We are trying to get a better idea of the forces we are generating at the tip of the throwing arm. We have invested in a high speed camera, 300 frames per second. If we can measure the deflection of the carbon fiber extension we can easily calculate the forces since we already know the length, area moment of inertia and the modulus of elasticity of the carbon fiber.

Deflection of a cantilever
D=lbs x (L)³
__3 x I x E

D=Deflection
L=Length
LBS=Pounds of Force
I=Area moment of inertia
E=Modulus of Elasticity

We have started our public demos on Saturday September 20. We had to revert back to our old steel throwing arm while the new stronger extensions are being finished.

I will keep you posted (I promise) weekly. We are keeping a "little black book" of all our throws. We will be posting distances (approx.) after each weekend of throws. We will also be informing everyone of our failures and successes. All of us are facing similar problems with strength of materials versus minimizing the amount of mass to rotate. Tweaking a machine to maximize the throw and still not break a component is still the name of the game. If we have any successes or insights we will try to pass them on to those who may be interested. We are not afraid of failure. We expect to fail a lot of the time before we finally get something that works. This is the first major renovation of Yankee Siege from its original design. We hope to increase our efficiency from a paltry 5.9 percent to something approaching 8 percent.

We are trying to approach our design from a more scientific/engineering angle. That means getting some hard numbers (no assuming) on the forces involved. So if you want to hear about failures this is the web site to read. Hopefully we will have a few successes. Time is running out. Only a few weeks to Punkin Chunkin. It always seems to come down to the last couple of weeks when everything will hopefully come together.

I hope everyone has great and safe practice sessions. This year promises to be very competitive with Pumpkin Hammer, Merlin, Trebarbaric and any unknowns. Pray that nothing breaks!

Steve Seigars, YS

Mid May 2008

2008-05-10T21:39:00.003-04:00

Yankee Siege Goes Commercial!

Yankee Siege is now for hire. We are available for rent for a day or we can travel to your site.

We have recently been contacted by Medieval Fantasies Company to shoot a commercial for a company that sells electronic monitors for power companies.

The shoot was in early April. Weather was cold and rainy the first day with lots of mud. The following day was bright and sunny but windy. Crushed gravel and stone had to be hauled in to control the mud. We threw 44 pound monitors which smashed into the field about 500 feet down range. We also crushed monitors with our ten thousand pound steel mace ball dropped about 20 feet high from a crane. And, did I mention, we also hit our crane (twice) with a 35 pound rock which spit out backwards from the treb and another 35 pound rock that went straight up and came down directly on the roof of the 1950 NorthWest model six crane, almost creating a new skylight! Oh well, I guess we need more practice in throwing objects other than pumpkins.

We ended up, removing 5000 pounds from the counter weight, and finally had the machine tuned to throw 40 pound objects. The second day went very well, with approximately 20 shots, with no mishaps, and very predictable throws.

The good thing about the shoot, is that it forced us to set up the machine early in the season, instead of waiting until September. The only thing bad about setting up early is the ice and mud. Ice had to be melted off the steel with a blow torch to get parts to mate. We can usually assemble the machine in four hours with a crew of six. It took us three times as long because we had to fight the weather.

We also had trouble getting the old NorthWest crane going (it hadn't been started in over a year). Something internal had froze (ice or rust) and the fuel pump wasn't working. Thanks to Chuck and Ken (two master mechanics) they finally were able to fire up the 1950 six cylinder Murphy diesel engine and get the job done.

The Museum of Science will be visiting our test site on June 30. The museum has a traveling group of teachers that visits sites of interest. They are planing a treb exhibit at the museum. They would like to learn more about trebs and to see a life-sized treb in action. I guess I will have to "bone up" on my physics!

Finally technical drawings of the new steel/carbon fiber throwing arm are completed. Nim-Cor of Nashua has fabbed the nine foot carbon fiber extension. End fittings (aluminum) will have to be fabbed and glued on with epoxy.

Copies of the final drawings of the new arm will be posted next month. These are fairly crude drawings (I'm not an engineer). I hope everyone can decipher them. I will scan them in so that everyone may see exactly what Yankee Siege is doing. And yes, these are the real drawings! We don't believe in playing poker. Yankee Siege believes in total transparency. We believe in sharing knowledge, information and insights. And yes, it's o.k. to criticize the design.

Next month I will be posting a more technical paper on the design process and the rationale for the new throwing arm.

P.S. Hope to see all the Pumkin Chunkin teams in Leesburg, Virginia, on June 7 for the grand premiere of Costa Mantis', "Flying Pumpkins the Movie".

Steve Seigars, YS

Mid April 2008

2008-04-12T21:51:00.005-04:00

The more and more I read about the physics of a trebuchet, the more I realize how little I actually know about the incredibly complex dynamics and the forces involved in accelerating an eight to ten pound object. If the motion of the machine were not so damn quick, I think we would all have a better intuitive understanding and a deeper fundamental understanding.

I have spent the last two months with two treb simulators (WinTreb and A-Treb). These simulators are a great aide in developing a good understanding of the "split second" motion of these machines. The ability to slow down time is invaluable to see what is actually occurring. What one thinks ones "sees" in real time, is often quite different from reality.

These simulators appear to be quite accurate. We have inputted the Yankee Siege parameters into these simulators and they have predicted very close to our actual distances thrown (within + or - 2%). As everyone knows, these machines must obey the laws of physics. (Although sometimes they appear to defy these laws).

Variations in the distances from throw to throw appear to be related to the time of release. (Excluding, of course, wind). There is a very small window of time in which to release for maximum distance. Plus or minus one tenth of a second can make a huge difference. (Small machines are even more critical - in a small machine everything happens quicker, making timing more difficult).

I've had to use these two simulators to explore as many ways as I can, to redesign Yankee Siege. One of the limitations of A-Treb is that it does not allow very high counterweight to missile ratios. Yankee Siege is now running a ratio of 1400 to one, (14,000 pound counterweight to 10 pound pumpkin). WinTreb will allow higher counterweight to missile ratios.

I do like A-Treb's graphs of forces on the machine. One very interesting note is that Yankee Siege has a reaction force on the axle of 100,000 pounds! (The force on the axle experienced when the counterweight reaches bottom).

A-Treb's graphs of acceleration and velocity of the throwing arm, really help one understand what happens as the counterweight "bottoms out" at the lower part of it's travel, causing the throwing arm to greatly accelerate. It also helps one visualize a transfer of energy from counterweight to throwing arm to sling. Each part of the machine will momentarily "stall" and as a consequence of the principle of conservation of energy, that energy present in the one moving part will have to be transmitted to another part of the machine (conservation of energy says that throughout the cycle the total energy of the machine will remain constant). Energy is conserved - you can't get rid of it! If one part of the machine "stalls" (no kinetic energy), then another part of the machine must possess the rest of the energy (either in kinetic or potential energy). Yankee Siege, for example, has 247,000 joules of energy stored in its counterweight. (14,000 pounds raised 12 feet). Throughout the cycle, that entire 247,000 joules must be accounted for. A-Treb has some nice graphs that show the relative partitioning of energy between the counterweight throwing arm and missile throughout the cycle.

In addition, angular momentum is conserved. As the sling and projectile swing around (due to centripetal acceleration) and finally overcomes the throwing arm, there is a dramatic increase in the moment of inertia of the beam/projectile combination. The projectile, as a consequence of its change in radius relative to the axle, "steals" some of the angular momentum and energy from the throwing arm, causing a slowing of the angular velocity of the throwing arm with a dramatic increase in the tangential velocity of the projectile. (Analogous to the skater who slows her spin by extending her arms).

As they say, you don't have know how a car works to drive it. But, if you want to know how to design a better car then you had better know every detail of how it functions. Yankee Siege is a "dumb design". We win only by brute force. It's time to re-design in a "smart way". We have to find a new way to more efficiently transmit a greater portion of the 247,000 joules of energy available to the projectile.

The single biggest "consumer" of energy is the throwing arm. Our throwing arm is a tapered steel built up I-beam weighing 2600 pounds! It takes a lot of energy to rotate such a large mass. Yankee Siege was designed to throw larger (300 pound) projectiles. Yankee Siege is very inefficient at throwing small (10 pound) projectiles. If we can design a less massive throwing arm, that won't break, we could throw significantly farther. Simulations with WinTreb show that with significant reduction of the throwing arm mass we could be throwing over "4000 feet"! Only one problem, we only have 2500 feet at our test site! 4000 feet seems almost too good to be true. Could the simulator be wrong? Where would we practice? Could a pumpkin take the g-force? The goal of the trebuchet division should be to beat the air cannons. Could such a machine be built? Should I wake up and smell the coffee?

Perhaps we should be a little bit more conservative and not go for the "ultimate machine" and aim for a more realistic 2500 foot machine. This would not require re-designing the whole machine but perhaps re-designing only a portion of the throwing arm. We have cut our existing long end of the throwing arm off about three feet from the axle and will be bolting on a new long end.

The new long end of the arm will be fabbed from ASTM A-572 steel, 3/16 inch thick plate, starting with a cross section of 12 inches by 12 inches and tapering to 3 inches by 3 inches over 23 feet. This will give a total weight of approximately 500 pounds. (Compared to over one thousand pounds for the old arm). 500 pounds is a huge savings in weight!

A note about A-572, grade 50, steel: this is a nobidium/vanadium low alloy structural steel with a minimum yield strength of 50,000 psi. Compare this to A-36 (mild steel) with a minimum yield strength of 36,000 psi. It (A-572) is easily cut and welded with no reduction in strength. (This is not a heat treated steel and will not degrade in strength in the heat affected zone of the weld).

The last nine feet of the tip of the arm will be a carbon fiber cantilever (clad with Kevlar for impact resistance). The carbon fiber tip be a "bolt on item", with the option of going to an aluminum 9 foot extension if the carbon fiber should fail. The carbon fiber will weigh less than 10 pounds! (A savings of over 35 pounds over the old extension).

We have decided on this "hybrid" arm for several reasons.

First, a total carbon fiber arm would be prohibitively expensive and perhaps not as forgiving as steel with regards to impact resistance. (When carbon fiber fails, it fails catastrophically without warning).

Second, steel, although heavy, is very stiff and easily fabricated and repaired in the field. An A-572 tapered steel arm, would make a relatively light strong arm. I have worked the numbers for a cabled stayed steel arm and came out with very little weight savings over a cantilever, with a lot more complexity. We have decided to keep it simple, with a pure cantilever. (I like the "looks" better, also).

Third, the part of the arm closest to the tip is the most important area of the arm to keep light. (Moment of inertia increases with the radius squared). It takes a lot of energy to rotate a mass that is a great distant from the axle. It is absolutely critical that the last nine feet of the throw arm be extremely light and stiff. What better way to solve this problem than to use a material that has the highest strength to weight ratio of all common structural materials (carbon fiber). We have decided to put the most effort where it counts the most.

Fourth, we have decided not to go with wood because of maintenance problems and reliability.

Fifth, aluminum: Yankee Siege is seriously considering going to an aluminum arm. Aluminum has a more favorable strength to weight ratio. A 23 foot extension to Yankee Siege's base arm could be fabbed out of 1/4 inch 7075-T6 aluminum plate with a yield strength of 75,000 psi! The main drawback of aluminum is that it can't be welded without a significant reduction in strength (40 percent reduction). Fabrication would require bolted connections (austenitic stainless steel bolts). Now I finally understand why airplane wings are riveted, not welded! The heat of welding destroys the tempering of the aluminum. There would be significant reduction in the weight of the 23 foot arm. (From 1000 pounds to 330 pounds, a 670 pound savings)! Aluminum is a material to seriously consider.

Nim-Cor Company in Nashua, NH. Phone 1(888)464-6267 will be fabbing the 9 foot carbon fiber extension. They have a carbon fiber automated filament winding mandrel system with the epoxy cured in an autoclave under pressure. Nice people to talk to, very helpful. They can only fab a uniform (prismatic) beam (no hand lay-up or tapering). They suggested wrapping the arm in Kevlar to give the arm some impact resistance. (An errant steel slip ring on the end of the sling could destroy the arm).

We will start gathering materials and start fabbing as soon as good weather comes.

Last but not least, perhaps the hardest part of the whole project is telling your wife how expensive the new carbon fiber extension will be!

I would appreciate your feedback! If you think this line of reasoning to totally foolish I would like to know. Do you have any suggestions? I would like to have an open discuss. We are all facing similar problems with strength and weight.

The Yankee Siege team is very excited over the new arm. Will it work? Failure would be o.k. Just not in competition! Looking forward to your feedback.

P.S. Next posting mid-May

Steve Seigars, YS

Mid January 2008

2008-01-20T18:23:00.000-05:00

I found a great article on the physics of a trebuchet. It is entitled "Siege Engine Dynamics" written by Mark Denny and published in the 2005, European Journal of Physics pages 561-577. It can be downloaded for a fee or if you have access to a major university library it can be downloaded for free. This paper is a bit hard to digest, unless you have a strong math background, it may not be worth reading. Some of the symbols are not very clearly defined, but by reading it several times most readers would be able to decipher the meaning. (I had to read it about five times before understanding it fully).

I have spent the past two months trying to design a new throwing arm for Yankee Siege. The team has narrowed down choices of shapes and materials to three or four different materials/configurations. (More about this later).

Before going ahead with a new lighter throwing arm, I first of all, had to determine if there would be any benefit to a lighter throwing arm. How far is Yankee Siege away from the "speed limit of a trebuchet"? I call this the SPLAT law. What is the SPLAT law? There is an upper limit of speed that no trebuchet can exceed (catapults do not have this limit!). This limit, is the speed due to the acceleration of gravity. The center of gravity of the counter weight can NEVER fall faster than the speed due to the acceleration of gravity (32 feet per second per second). This is the speed of a free falling body. The counter weight will, of course, always fall a little bit slower than a free falling body because it has to overcome the inertia of the throwing arm.

IF Yankee Siege has added so much weight to the counter weight that the counter weight speed is very close the speed of a free falling body, then making a lighter arm will only have a very slight marginal effect on the throwing arm angular velocity (speed of rotation) and therefore, will not throw significantly further. I am still searching for that mass less throwing arm which would offer no resistance to rotation and would allow the counter weight to free fall and therefore attain the maximum angular velocity.

The other major factor that limits the angular velocity (speed of rotation of the throwing arm) is the length of the short end of the throwing arm. The greater the length of the short end (counter weight end) of the throwing arm, the slower the maximum limit of the angular velocity (rotation) of the throwing arm. (It takes longer for the counter weight to drop because it has a longer distant to fall). Another way to look at this is if you increase the length of the short end to infinity, then the counter weight would have an infinite height and would never complete its fall and therefore the throwing arm would rotate infinitely slow. This is the main reason why large scale trebs have relatively slow moving (rotating) throwing arms. Their angular velocity is limited by the SPLAT law and the SPLAT law is reached at a lower angular velocity. Conversely, a small scale treb with a very small, short end of the arm, can rotate very quickly because the counter weight doesn't have very far to drop and can complete the cycle very quickly.

Yankee Siege has a 12 foot drop of the counter weight. If we are close to the ultimate speed limit, the counter weight should take .86 seconds to fall. (The time it takes a free falling body to fall 12 feet). Yankee Siege takes a little over 1 second to fall 12 feet (timed with a stop watch off of Pumpkin Hammer's website showing Yankee Siege firing). Thank you Pumpkin Hammer-by the way you have a great website.

The other consideration is the fact that the counter weight does not drop straight down. And we would expect it take a little longer to drop if it doesn't go straight down but takes another (non-vertical) path. We may be even closer to the limit than we originally thought.

The conclusion from this discussion is that Yankee Siege is approaching the speed limit and that making a lighter arm will help but not dramatically increase the angular speed of the arm because we are so close to free fall.

More on the new throwing arm details next month. Hope to hear you feed back!

Steve Seigars, YS

Yankee Siege Latest

2008-01-20T18:08:00.000-05:00

Late December 2007

2007-12-25T20:17:00.000-05:00

Spent most of the time this weekend pouring over books on beam theory and strength of materials. I found two great books by J.E. Gordon written in the 1960 & 70's entitled "Strength of Materials and Structures" and "The New Science of Strong Materials". These books are essential reading for anybody interested in designing any structure. Mr. Gordon has quite a talent of clearly and concisely explaining the theories of bending and elasticity. These books are quite readable and anyone with a basic understanding of algebra and geometry can easily digest. These are great books for the layman and are a good introduction to further engineering studies. After reading these books, you are left with a more intuitive understanding of why materials behave as they do.

As I am wandering through these books, I am constantly thinking of how these principles apply to a trebuchet. There is a good explanation on the strength of a material and, its elasticity and its density and how that relates to its strength to weight ratio.

Mr. Gordon points out that the specific modulus of elasticity (that is its stiffness per weight) is virtually the same for all the common structural materials. (With the possible exception of carbon fiber composite). This explains why there are several choices of materials to construct a throwing arm with no clear cut winner in stiffness to weight. Whether one uses steel, aluminum, wood, fiberglass, titanium, etc... there is not a lot of differences.

I want to make one important distinction between strength and stiffness, they are not the same! When it comes to strength and weight there is quite a difference from material to material. Titanium is a clear winner of all the metals. Carbon fiber is a clear winner of all the non-metals in regards to strength to weight.

That comes to the next question. What is more important in designing a throwing arm? Is stiffness or strength more important? The obvious answer is that both are important. The throwing arm must be strong enough not to break and at the same time be stiff enough not to deflect too much on the pull down as to produce too much of a recoil upon release of the trigger.

Note: Yankee Siege has developed an annoying recoil of the arm upon release of the trigger. We have added so much weight to the counter weight that upon release, the throwing arm snaps back and creates a "hop" of the pumpkin off the ground and a subsequent oscillation of the arm that leads to a quite unpredictable release of the projectile. We are trying to time the release of the projectile to an arm that is oscillating in its own mode of frequency.

This brings home the point of the difference between strength and stiffness. Stiffness relates to elasticity. A throwing arm may be quite strong and at the same time quite flexible (elastic), leading to greater deflections when cocked. (Note: an increase in the cocking angle will cause less deflection, with no deflection if cocked to 90 degrees).

For example: two identical size throwing arms made out of different materials will exhibit different amounts of deflection even if they had the same tensile strength. Mild steel and some aluminum alloys have identical tensile strength but aluminium will deflect three times as much upon pull down (aluminium has one third the elasticity of steel).

If deflection is deemed an important criteria, then choice of an appropriate modulus of elasticity is of critical importance.

Yankee Siege is trying to figure out a way to take advantage of the elasticity of the beam and figure out the frequency of the elastic oscillation and to take advantage of the "forward snap of the arm".

Perhaps a very elastic beam would be a help not a hindrance! If we could only time it right and design an arm to oscillate at the right frequency so that the release would coincide with the forward "snap". Cellulose is very elastic-maybe Trebarbaric knows something we don't! I'm still looking for the ultimate material!

A simpler approach would be to design an arm that is very stiff (steel would be a good choice as it has the highest modulus of elasticity of all the common structural materials). A very stiff arm would deflect very little and would not be a nightmare to time the release because the deflections are insignificant (they would be very small but high frequency).

We are still in the design phase for the new throwing arm. We have not made any final decisions as to the materials or combination of materials or configuration. I have now finished re-reading Gordon's books for the third time and I am still learning something new each time.

As you can probably tell from these musings, the Yankee Siege team is somewhat obsessed with designing an energy efficient arm. I spend the majority of my waking hours thinking and reading and imagining. I keep thinking that maybe if read just one more book, one more page, one more article that the ultimate design will suddenly become obvious.

In reality, there are probably a dozen ways to construct an efficient arm. We may end up with two or three different arms that can be bolted on and see which one works best.

I think the hardest part of the whole design process is making a final decision! Committing to a final design means that you have said to yourself that this is the best design that I can come up with at this time, given my level of knowledge at this time. Perhaps I should wait a little more time, gain some more knowledge, and redesign. At what point do you say enough is enough. At what point do you pull the trigger and let gravity take over!

I'll try to keep everyone posted monthly. I enjoy hearing from you all. Yankee Siege team would like to hear your feedback. If you think we are proposing some utterly foolish idea, we would like to hear from you. I hope some of these discussions will help other teams, as well as Yankee Siege. I would especially like to hear from Pumpkin Hammer, Trebarbaric and Merlin. I think that we should keep in touch throughout the year. I call these teams, members of the "1000 Foot Club". We are the members of an exclusive club that have broken the 1000 foot mark (no easy accomplishment). I hope I haven't left anyone out. Anyone may join the club-you just have to throw more than a thousand feet in any competition. By the way, Yankee Siege fully recognizes Trebarbaric's throw of 1866 feet!

Yankee Siege hopes to start a new club in November, (the 2000 Foot Club)! Wishful thinking!!! Hope to have several new members!

Steve Seigars, YS

Mid-November 2007

2007-11-22T21:02:00.001-05:00

Punkin Chunkin for 2007 has come and gone! Merlin(King Arthur) and Pumkin Hammer have built new machines and promise to be quite competitive next year. They were relatively untested machines for this year but I can see that both machines, if tuned, could easily throw into the 2000 foot range. Yankee Siege has pulled off another first place for the fourth year in a row. The only other team to do this in the treb division has been the legend King Arthur.

Now is the time for reflection and to decide to what direction we want Yankee Siege to go. Yankee Siege has always been known as the brute force machine. We have enjoyed throwing 200 to 300 pound pumpkins as well as 10 pound pumpkins. We have now come to a cross road. We have come to the realization that a single machine can not be built that can efficiently throw a large as well as a small projectile. The massive throwing arm needed to throw a heavy projectile severely increases the moment of inertia, which requires a massive counterweight to accelerate the arm (we have a 14,000 pound counterweight). Our throwing arm weights 2600 pounds. Most of the potential energy of the counterweight is used up in accelerating the arm. A minuscule amount of energy actually gets into the pumpkin. (A paltry 5.9 percent of the potential energy of the counterweight). A machine that is only 5.9 % is a very poorly designed machine! We are, by far, the most energy inefficient machine in the whole competition. By contrast, King Arthur, is 57 percent efficient. King Arthur is a very well designed machine from an energy efficiency viewpoint.

Early in the spring of 2007, we cut the end of the throwing arm off about 3 feet from the axle and mounted a companion flange in anticipation of building a new lighter throwing arm. We now have the option of bolting on a newly designed arm or if that arm does not work out to default back to the original arm. This, bolt on modular design, would give us total freedom to test new arms and see what works. If the new arms failed, we could always go back to the old "tried and trued" arm. Our basic machine (winch, frame, axle, counterweight, etc...) have proven themselves over the years reliable and quite robust, so the decision was made to keep the basic machine "as is" and modify the throwing arm to be lighter. The new throwing arm will be specifically designed to throw 10 pound pumpkins and therefore giving up our ability to throw 300 pound pumpkins. To remain competitive, we are forced to make major changes in the throwing arm. The throwing arm is the "energy hog". It is robbing us of energy to accelerate the pumpkin.

The team has been racking our collective brains trying to come up with the "ultimate throwing arm".

What would it be made of?
What would be its shape?
How long?
What would it weigh?
Would it be able to be repaired in the field?
Would it be able to be modified?
Would it break?
What would it cost?
Would we be able to build it?

All these are questions to be answered and hopefully solved. I'm still looking for the massless arm! (I'm told that somewhere, perhaps in Area 51, or on another planet there have been sighted massless throwing arms designed by an advanced civilization)! Or maybe we could locate one in a junkyard, we all know you can find anything in a junkyard. We'll keep on looking!

We all know there is no material or combination of materials that will satisfy all design considerations. Light and strong are two incompatible parameters.

By contrast, Yankee Siege is so inefficient(5.9%), that a small increase in efficiency will bring large increases in distance thrown. If we could just get Yankee Siege to be 10% efficient we would be throwing 2881 feet(14000 lbs. dropping 12 feet and throwing a 10 lb. projectile).

Anyone who has been working with trebs for a long time knows that designing a treb to throw long distances is no easy task and is full of potential pitfalls. The best thought out plans can sometimes fail by overlooking the smallest detail. The weakest link will always show up sooner or later. There are often unexpected events happening at such high speeds that can't be seen by the naked eye. It's hard enough to design a structure that is static. It becomes exponentially harder to design something from a dynamic viewpoint.

We all learn from failure (we learn more from failure than success). When something breaks, we know for sure it wasn't strong enough. When something doesn't break, we don't have a clue as to how much we have "over-engineered". After all we trying to push our machines up to ,but not beyond the breaking point, just light enough for maximum acceleration, but not so light as to break. So break a few arms and find the limit!

We'll keep you posted on our progress.

Steve Seigars, Yankee Siege

Punkin Chunkin 2007 World Champions!

2007-11-06T15:25:00.000-05:00

The Punkin Chunkin competition is over for this year, and once again we are the World Trebuchet Champions with a winning throw of 1658 feet into a strong wind! The scoreboard with our winning throw is at left. (Photos enlarge when you click on them)

The convoy all packed up and departing area 64 for the long drive back to New Hampshire.

Day Three

2007-11-02T17:26:00.000-04:00

Thursday November 1, 2007 (team member Valerie B-day) Practice day

First two shots fell out of the pouch. And the controversial 1st successful practice shot was thought by the forward observers who didn't see the pumkin but heard it land at 2k plus! We switched to a more encompassing pouch and and tried some 1/8th wire cable and had moderate shots at the 15 to 1600 range. The last shot of the day was very high (highest ever from YS). Our good friends Pumkin Hammer and The Magic of Merlin arrived. Pumkin Hammer got off two shots and had one slip off the sling. Merlin arrived late and didn't get off a shot before dark.

Weather was warm and very little wind! Field is beginning to dry out although our two left wheels are slowly sinking into the soil. Bridgeville had several days of rain prior to our arrival. We will shore up the left side of the treb and wheels early Friday a.m.

Friday November 2, 2007 (Day one of competition)!
Very windy day, hurricane Noel off the coast. Strong north west winds!
Yankee Siege was the first of the trebs to throw! We decided to use a lower tragectory because of the strong head wind.
Good shot hooked strongly to the left at 1658 feet. Happy with the shot considering the windy conditions. Pumpin Hammer was next at 700 plus and Merlin 800 plus. Artemis threw 4th.

Costa Mantis has been filming about 20 teams for the past year and has hired a high speed camera crew that will give slow motion view of the machines at 1000 frames p/second. Can't wait to see the slow motion video of what's going on and can not be seen by the human eye of shot one!

A special thank you to Pumkin Hammer for their trebuchet running scoreboard. They have great team spirit and always think of the trebuchet division as a whole. I think the scoreboard is a great idea and it helps clear up some of the confusion during the pumkin chunkin competition. Also, thank Pumkin Hammer for always making reservations for Saturday night dinner at Big Fish.

Wishing everybody luck for day two!

YS

Yankee Siege Arrives in Bridgeville, Delaware

2007-10-30T07:00:00.001-04:00

Yankee siege arrives today for "Punkin Chunkin 2007", this year at a brand new venue in Bridgeville, Delaware. The new site boasts a field roughly twice the size as the one in Millsboro, where the event was held last year. Yankee Siege will defend it's Adult Trebuchet class title throw of over 1400 feet. We hope to best our 2005 World Record of 1702 feet set in 2005, and with undisclosed new improvements to the machine, perhaps 2000 feet will be attained.