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!
Saturday, October 24, 2009
Monday, October 5, 2009
Yankee Siege Destroys Main Axle Bearings - October 5, 2009
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.
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
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.
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
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
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
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