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Trebuchet does not release load Answered

Have built a pallet/ man sized trebuchet in a 4th grade class project. Looks great, swings well, but the tennis ball load is either released before the sling swings up, or not at all (slams against the arm). Have used 2 ropes with a shallow bag.

Any suggestions? (Kids were disappointed on Friday)



7 years ago

I already found out one part is missing: the 'release pin'. Will study some designs and try to install one. I'll update after testing...

Does it have wheels or does it just sit on the ground?

It has rather massive wooden wheels on large nails: more for show than for actual use (not very round).

I could be completely on the wrong track here, but from what I can remember seeing on TV some years ago (I haven't bothered to google anything), it was important for the machine to be able to roll slightly forward/backward on it's wheels as the load and counterweight swing through their arc. I also don't remember anything about a release pin, the load just flew from the bucket at the top (or there about) of the arc. A large machine with no wheels would rock as the weigh tswung, and the smallest ones would flip over. It seemed that functioning wheels made the trebuchet more efficient.

I would guess for a smaller machine it's more important to have the release pin calibrated than the wheels for the motion -- In fact, I'd say the wheels allowing the machine to move backwards extracts some energy from the projectile (action/reaction).

I'm with Frollard on this - a trebuchet that can move will lose power to the recoil.

The majority of "real" trebuchets were built in place, not wheeled there.


7 years ago

It could be a couple of things; your pouch is not releasing the missile cleanly, or its not disconnecting from the release pin at the proper point in the swing arc. Or, it could be a combination of both. The only way way I know to correct the problem is to experiment a little.
You can test the pouch for release by just using it like a normal sling a few times. If it works then you need to adjust the release pin by changing the length and/or the angle. Try to observe what's going on and play around with it until it works.
It takes a little patience but It'll come around.

Please show us a picture of how the sling is attached to the arm. It will be that bit that needs tweaking.


+1. a tennis ball may be too light for it also.

We were doing the first tests: a bucket half full of sand as counterweight with tennis balls. Other projectiles and a full bucket of sand (or scrap metal, why not...) will be tested later. I don't want to be too hard on the trebuchet while testing, since the pallet wood is not the best quality (splits). It needs to last the full month of April (middle ages theme in the school- I'll try to make a slide show)

On Friday my camera turned out to have a low battery, so I will submit on monday


The angle and length of the release pin are critical.