Thursday, November 22, 2007

Mid-November 2007

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

1 comment:

Wes Frank said...

Hey Steve,
Tre Barberic is only 13.5% effecient with a wood arm and a rotating CW so don't stress to much the new wave of machines are much more effecient by nature of design because of leverage or length of drop the only way to get high % with our type machines is to redesign our CW drop buy proping or some thing scary like that.