AZtreb - Trebuchet Enthusiasts in Arizona

Our Trebuchets

3/20/2006

Bed Frame Trebuchet

Rob and I have managed to take advantage of the limited time we have and built a Trebuchet out of scrap lying around.  Our wives went out of town for a conference and we gathered all the kids at Rob’s house and looked around his garage for parts.  We found:

1 old bed frame (angle iron)
2 16ft 2X4s
1 6ft 2X4
1 steel closet rod about 27in long (surprisingly strong)
1 bucket of Random bolts, nuts and screws
The combined plates from our weight benches

During the construction process we also found

1 piece of plywood (about 30inX40in)
1 hardened steel rod ½ in
2 lengths of steel cable (one from the weight bench one random length of steel cable)
1 Burlap sac
1 tie down strap

 We had to brake down and go to buy a few parts

2 angled hook hanger things $1.99 each
2 hose clamps (the kind you screw tight) about $1 each
4 wheels on mounts $3.99 each
1 container of bolts and nuts $6.99 (we could have made it without this but it was getting annoying digging for bolts & nuts and we now have a handy organizer chock full of nuts & bolts)

 We took an old bed frame two 16ft 2X4’s and a 6ft 2X4 that were sitting in his garage and began planning.  We used a grinder to remove some unwanted rivets, drilled a few holes and added a few bolts and we had two similar triangles with a place for the axle almost lined up.  We set aside one 2X4 for the arm and used the remaining to create a frame to hold the two sides, the rest kind of fell into place.  End result the axel stood just under 5 ½ ft off the ground and the throwing arm was 6 ½ ft long with a Counterweight arm of 23in (not the best ratio, but I made a drilling error) making a total height unloaded of just under 12 ft.

I forgot to bring my triggers from home so we had to jury rig a trigger and that broke so we improvised and used a tie down strap.  The first few launches went very high but not very far.  The tie down strap was slowing down the release of the arm.  Unfortunately we grossly underestimated the force 180 pounds has while dropping three or four feet and we bent our axle (1/2 in steel rod) and before we could tune the Trebuchet the axle had bent down to the point it was getting hazardous to continue.  We will obtain a stronger axel or replace the axel with another ½ steel rod (I have one in my garage) and lower the weight to avoid axel bending so we can tune it to a better launch.  We are considering drilling a new hole for the axle in the arm but we don’t want to weaken it.  I will keep you posted as it develops and hopefully continue the saga of the Bed Frame Trebuchet soon.

Robert

1/23/2006

As it turns out we are a lot busier than we supposed.  The Big “A” Trebuchet is on an indefinite hold until I graduate or things slow down.  I continuously work and rework the plans but without the time to build and test a model it is a constant loop: I decide on a plan, I modify the plan, I reevaluate the plan, I step back to get perspective on my plan, I fundamentally change the plan, I decide on a new plan, repeat.  Once I get things going again I will keep you informed.

Robert

We are still working on the design of this Trebuchet we plan on soon having a plan from which to build our Scale Model.  The scale model will be roughly 1/4 size of the finished product.  We are currently working on acquiring supplies as well as time to hammer out the details but by our current estimates the Big "A" Trebuchet will be a 12 Foot Long 14 Foot Tall Frame with a 16 Foot arm.  It Should Launch a 12-14 pound Pumpkin or Bowling Ball about 100-300 yards.