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Interesting modification to the plans - similar geometry but streamlined construction - very successful!

Hi,
A few weeks ago, my friends and I purchased your trebuchet plans, and built a working trebuchet. I thought you might want to hear about it, so I thought I'd write up what we did.

We had to modify your plans for a few reasons:

First, our goal was to deploy the trebuchet at an annual camping trip we do 250 miles away from where we live in Chicago, so the treb had to be easy to disassemble, fit into a cargo van, and reassemble on-site.

Second, none of us are very handy carpenters, so we wanted to simplify the design as much as possible.

Third, we wanted to keep costs a little lower.

We made several changes to the design based on this:

  1. Most of the lumber joints in the treb are made with 1/4 inch bolts. This worked out great we had to do a little more work drilling, but in the end, we broke down the treb in under 20 minutes, and had the frame standing on-site after about 30 minutes of work.
  2. The base is built in two 8' pieces joined together with bolts and 2x4 straps. This worked well enough, but we did see some significant wear around the joint after about 20 launches.
  3. The outriggers are much simpler -- they are a simple triangle of 2x4s joined together and to the upright pieces with heavy-duty door hinges. This also worked out great -- we observed no wear or signs of stress on these pieces.
  4. We greatly simplified the assembly that held the counterweight. Instead of a bucket, we built a square frame out of 1.5" and 1" iron pipe, and hung 450lbs of olympic-style weights on it. This consisted of an upside-down U-shape made out of 1.5" pipe that terminated in T-connectors, and a 1" bar with the weights on it that slid in easily into the T-connectors. We secured the weight bar with normal plumbing end-caps. This was also very functional Changing the weights out required sliding a bench in place and a good deal of care, but the weights let us precisely determine how much weight we were putting on, and we observed no problems with the frame.
  5. We swapped out the 1.5" solid rod for the main pivot, and used a 2" galvanized iron pipe instead. This DID NOT work out so hot. It held for the whole time we used it, but by the end, the pipe had a smooth bend in it at what I estimate was about a 10 degree angle. We would definitely stick with a solid rod next time.
  6. Instead of using hose clamps to secure the lever arm in place on the pivot, we used sleeves cut from PVC pipe as spacers.
  7. We used a purpose-made trebuchet trigger instead of the suggested firing mechanism. I have no idea where this originally came from, as it came through a friend of a friend. 

We had some trouble getting the launch mechanism right -- we found that the release angle varied wildly if we changed the weight of the objects we were throwing. A heavier load would release much earlier than one 1/3 the weight. We experimented some with using quick-release knots to do the release at a fixed angle, but were ultimately unsuccessful in getting something to work as reliably as the rod and ring setup.

Thanks for the plans!

M. Babinski

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