Zheng3 Penny Catapult
Description
Here's a basic torsion catapult. It uses one or more elastic bands to launch a U.S. penny if you print it at 1:1 scale. You probably won't get enough torque to be impressive with fewer than 3 bands.
Penny not included!
Instructions
Feed an elastic band through each of the bores on the side braces. Tie it through the bore on each winding key. Slip the end of the throwing arm through the rubber bands. Repeat with as many rubber bands as will fit through the holes. Needlenose pliers will help here.
Twist each key 10 times and then lock it in place by inserting the locking tenons into the square holes on the side braces. The more twists, the more launching power you'll have. Careful, pennies can sting, especially if you take an Abe to the forehead.
Flagrant stagecraft alert: the clever-eyed among you will note the use of black electrical tape to keep the throwing arm cocked for the photo.
If you need a target, try the Seej basic bloxen: thingiverse.com/thing:23620
UPDATE 6/2/12! Thanks to Thingiverse user Wauter for pointing out some geometry problems in the winding key and side braces. These have been addressed in zheng3_catapult_clean.zip
Seej is a tabletop wargame based around 3D printing. Check out s33j.net for rules and more information.
You can change the payload's arc by raising the front of the catapult. Have fun storming the castle!
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Seej is an awesome idea! It reminds me of my favorite childhood boardgame called Crossbows and Catapults! http://boardgamegeek.com/board...
Awesome! Could you separate out the parts at some point? I tried a couple of times to print one for my kids, but a couple of the crossbeams keep curling up, and so I need to cancel the whole thing. :/ If the parts are broken out, I could deal with those problem parts separately.
very cool, the beams on mine are a very loose fit though, so needed glue, is that normal? how much allowance did you make on the dimensions?
I'm printing on a MakerBot replicator and the bores are quite snug when I print with black ABS.
Here's a pic of the bore and crossbeam in orthographic view so you can see the (fairly lax) tolerance.
You might have better results if you scale the crossbeams up in X and Y just a bit.
The winding keys on the sides should be very loose so that you can take them in and out easily.
Properly called a Mangonel, I beleive.
Yes! garyacrowellsr is correct!
"Catapult" is a catch-all term for siege engines like this. I think this is somewhere between a mangonel and an onager. Call it what you like, as long as you have fun with it.
The design for this catapult/mangonel/onager is loosely based on one from
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The Art of the Catapult
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, specifically pages 127-136.
Could you possibly make the arm a separate file, or even a SCAD, for us non-americans? :) Otherwise, excellent stuff looks great :D
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This works a lot better if you use string instead of elastic bands, loop it backwards and forwards a few times, then tighten (fiddly). Pennies go quite a few metres then :)
It's all about the torsion.
Sooner or later somebody's going to use a guitar string or some piano wire. I'd love to see how that works.