13 replies to this topic

[Kuhlschrank]

OK, guys, my AP Physics teacher is having us build "potato cannons"(we're actually launching tennis balls). I was wondering if anyone has decent experience building them and could give me a few pointers on designs and materials.

[flashflint]

first are you makeing a combustion or penumatic gun.
try "www.backyardarsinal.com" I think thay have info on bolth.

[One Man Clan]

I'm pretty sure LGLF knows a thing or two about potato guns Tyler. I have some experience with them as well. I still have my first one I ever built in my garage. I'm not sure when it's due for you, but if its not before the 29th, I can bring it to the LCM war.

What are method are you guys using to launch them? I mean in terms of fuel; compressed air, or something simple like hairspray? There are also good plans online at spuctech.com (I think that's the sight). Very basic PVC launcher.

[cxwq]

Design criteria please. Is the goal distance, elegance, size, ROF... ? Propellant specified or left to your own imagination?

Tennis ball launching requires 2.5" PVC which can be hard to find. I know spudtech has them (with adapters) but you may have trouble at the hardware store.

Safety note: if you're using PVC/ABS I'd stay away from oxygenated fuel mixtures. Stuff like that is best used in aluminum launchers which aren't so likely to explode on you.

[Kuhlschrank]

My mistake.
1) They are combustion guns and we are graded on distance.
2) Propellant is not specified, but he's obviously going to look into the method for safety reasons(it is a shool project after all)

Cx, when you say oxygenated, do you mean any combustible fuel whatsoever, or certain types I should avoid?

[cxwq]

Cx, when you say oxygenated, do you mean any combustible fuel whatsoever, or certain types I should avoid?

I mean use Right Guard or propane or butane but do not under any circumstances inject oxygen into the chamber with any combustible material. Your power in a combustion spud gun is limited by the amount of oxygen in the air inside your chamber. If you displace that air with pure oxygen, it will increase the power beyond what PVC can withstand. Because combustion spud guns are an inexact science, err on the side of safety.

I'd suggest getting a 4-5' barrel of 2.5" PVC and coupling that (probably with two bushings or adapters) to a piece of 4" PVC. If money is a concern, get a flint-style coleman lantern igniter and mount it through the chamber wall. If you can spend a bit more, there are electronic bbq igniters that are much easier to use and more reliable. Don't use hairspray because it will gunk things up. Make the chamber about 3-4x the volume of the barrel. Use appropriate cement - PVC cement for PVC, ABS cement for ABS, etc. Use primer. Let it dry for 24 hours before you test it. Less fuel is often better (air/fuel ratio) so experiment with the amount you put in.

Simple instructions here.

[Kuhlschrank]

Thanks for all your help guys, but
my teacher has given in to peer pressure from other teachers and we are now building trebuchetes because they cant explode.

Edited by Kuhlschrank, 13 May 2005 - 08:22 AM.

[userjjb]

Well I consider myself fairly experienced in trebuchet construction/design, so if you have any questions I can help you out.

Are you designing for max range like the potato launchers? What are you firing? Is there a dimension limit/counterweight weight limit?

[cxwq]

That's bullshit. He should just require remote electronic ignition and set them up behind a blast wall of some kind.

[Arcanum]

My science project last year and this year focused on trebuchets. Last year I altered the counterweights and this year I altered the projectile. I just returned from the state science fair at University of Illinois and received a Silver Award for my project and report. My friend received two 500 dollar college bonds for her work on water purification, so people take this pretty seriously. If you want to look at some example plans to base yours off of, or simply purchase them, go to trebuchetstore.com and look at the science tennis ball trebuchet. I'll see if I can't get a link.

Edit: http://www.redstonep...t_catapult.html

Edited by Arcanum, 13 May 2005 - 02:10 PM.

[boltsniper]

I built a floating arm trebuchet in college. We used to use it lob eggs (*cough* and golf balls *cough*) about 300-400 Yds into another apartment complex. Great fun. Floating arm trebuchets are capable of much better ranges than a comperable sized conventional trebuchet. The weight moves linearly down instead of in an arc which allows greater energy transfer into the arm. They are a little bit more complicated but it will pay off.

[Jakethesnake]

I built a 5 1/2 ft trebuchet in shop class in high school, it shot pretty good, but the floating arm ones are better. Bolt, how big was yours?

[The Infinite Shindig]

I built a floating arm trebuchet in college. We used to use it lob eggs (*cough* and golf balls *cough*) about 300-400 Yds into another apartment complex. Great fun.

You know, it occurred to me that Hunter's Ridge is about 300-400 yards from my apartment at Terrace View. ::Get's Ideas::

[userjjb]

FAT and FAT2K machines may be more efficient, but they also tend to be more complex and problematic. More moving parts = higher chance of mechanical failure. If you're in a competition with size restrictions, (must fit in a 1 meter cube etc) they're the way to go, but for sheer power you can't beat a super-propped treb. I have one that's six feet to the axle (convenient size for working on/transport),with 200lb of CW, that launches a 1 lb lead ball 1400 ft. Needless to say when that thing hits stuff it goes boom.

Edited by userjjb, 13 May 2005 - 04:06 PM.