Yet Another Trebuchet

[charlie b]

Before summer vaction ended three of the boys in the neighborhood wanted to make and use a trebuchet. I ripped the parts, they did the cross cuts and angles on the SCMS - using stops I set. They did the glueing and stapling, the drilling and figure out the hinged side bracing method.

Knowing it'd probably end up being stored in my shop, I came up with the idea of making it modules that could be assembled when needed and stored in a 48" x 34" x 12" space. Also makes it easier to put in a vehicle and take to a park to play with. Not surprising that it can draw a crowd.

Hurls tennis balls nicely but we haven't worked out the sling lengths and weights for water balloons. All attempts so far have thrown the water balloon almost straight up - and it's a crap shoot as to which way to run to get out of the way.

(all one line so watch the line wrap)

one was so far away from anything I've done so far - but fun.

charlie b

[Swingman]

Looks/sounds like fun ... and keep a close eye on your piano.

[gfretwell]

Try this guy

made one last year that would throw an orange over 100 yards

[charlie b]

Guess you didn't use the URL, or if you did, missed the text that says "It is based initially on Ripcord's trebuchet design." I beefed it up a little by doubling up on some of the components, reinforced the areas around the steel pins/axles and made it so it comes apart for easy transport.

Will have to try an orange and maybe an apple. People don't seem to mind as much if they get hit by and orange or an apple, as opposed to a golf ball, baseball or round rock.

charlie b

[gfretwell]

I really had a bunch of sites I used to make my own design but I thought this guy linked most of them. I didn't make the one pictured. I did read the theory and design articles. The trick about throwing high or low if the shape of the release hook and the length of the straps holding the pouch.

[charlie b]

snip.

OK - how about what you discovered" - longer sling cord lenghts = longer distance? - shorter release hook = higher trajectory and shorter distance?

What about the initial arm angle when cocked? Take it all the way down so the sling chords are horizontal or up so that only the pouch is on the "tray"?

I'm using an allen wrench, the kind with the ball on the long end, for the release hook. Also have some peg board "hooks" with the ends angled up a little. What did you use?

Found that after 30+ tennis ball throws with the weight box loaded up with rocks and bricks, that the arm's "axle now has a slight bend in it. Will bump the axles up to 1/2" and that should solve that problem.

Any hints, tips, suggestions that will improve predicatbility and range would be much appreciated.

charlie b

[gfretwell]

I used a 2x2 oak arm about 5' long on a frame of "patio ties". The pivot was a 4x4 with 3/4" pipe in it that the arm was morticed into. The pins in the frame were 3/4" bolts with the heads cut off that were a nice fit in the pipe. The threaded part was through bolted in the frame. The heavy end was an "H" beam of 2x4s about 14" long with the top/bottom chord lapping the 4x4 and through bolted. The weight was 2 bags of lead shot and anything else heavy I could find. I used a piece of 3/16 brazing rod for the hook so I could bend it easily. You really want it to curve, not be a sharp angle. The release hook was separate, a gate latch. The launch track was a piece of 3" PVC ripped in half I played a lot with the sling length but something that hangs a bit below the pivot is a good place to start. A lot depends on the height of your launch guide. I doubt any 2 of these will throw the same so you will be experimenting a lot. Google is your friend. There are lots of sites about these things.

BTW I had to take mine down when the neighbors started complaining so be aware everyone will not get the joke.

[mac davis]

Charlie.. DON'T throw 1 pound "salmon ball" ball weights, either.. DAMHIKT

mac

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[mac davis]

Charlie.. trying to dredge up things from senior memory here, but..

Seems like we'd start with a sling that was about 1/2 of the length of the arm and adjust from there.. you have it right when the sling wraps around the arm when "dry firing".. If I remember this right, adding length to the sling makes it release later and throws higher/farther UNTIL it's too long.. (probably doesn't help)

The arm at "rest" should be at a 45 degree angle from the rails or sling bed.. On a classic setup, the sling and pouch lay on the bed/rails when the treb is "cocked"..

We used replacable plywood hooks, so that the length, hook angle, etc. was adjustable.. the hook and release are critical to a clean, repeatable shot...

If you haven't seen this site already, Charlie, it's where most of us started out and refer to a lot:

The Grey Company Trebuchet Page

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