catapult
 

I have to build a catapult for ap physics, it has to be 1 meter by 1 meter, and it has to be able to launch a 2.5 pound mass from 150 - 300 feet, I'm trying to beat the record at my school right now, and my last catapult that I built could only go to 65 feet, so...you guys have any ideas on how to make one? I'll try to post a picture of my old model and my ideas from my new. The rules are you have to be able to cock the arm of the catapult back without touching it, and have a trigger device, you can't use anything electric, or gas powered. Right now I'm using springs and bungie cords to get my power.....so, can anyone help me out? any ideas?

What are you using for an arm, and are you allowd to have a crank-type cocking mechanism?

Medieval catapults were actually rather impressive, you might want to take a couple of design tips from them!

yeah I had a crank on my last one...

The arm diameter, elasticity, and counter point are going to be the 3 critical points in getting it to do what you want. Are you allowed to disconnect the cocking crank after the arm has been locked into the trigger? And can you use any materials that you'd like? For instance a high-tensile spring steel?

Are you using the word "catapult" as a specific term or a general one? What I'm thinking is why not build a trebuchet (possibly more efficient use of energy=longer yardage).

can you make a trebuchet? that might be the way to go... i dont really know that well tho...

http://www.tasigh.org/ingenium/small.html

It would be awfully hard to make an effective trebuchet with a 1 meter x 1 meter limitation though, doesn't leave you much room for the counterweight

you can use any materials, and yes you can remove the crank after usage, and it could be a trebuchet, but again don't know how to go about building it.

the pic on the site was cool, but theres no way that that thing can throw a 2.5 pound mass over 200 feet

You could make a floating arm trebuchet, that way you don't have to worry about room for the counterweight... and it's more effective than the traditional trebuchet.

By the way, are we talking that the whole thing has to be able to fit in a 1m x 1m square, or that the length of the main arm is a meter? Because that could make a huge difference. I built a floating arm trebuchet my senior year for physics that could do something like what you're describing, and the measurement of my arm was less than a meter long... but I can't think how I would've done it had the whole thing been really small.

Edit:
http://www.trebuchet.com/story.php/fat.html

If you decided to build a trebuchet, this would help.

Bit of advice. If you can afford it, lead balls makes a awesome counter-weight if your planing to use a trebuchet.

the whole thing must measure one meter in length and height when in a cocked position (should have said that before...sorry)

I'd recommend layered spring steel, similar to what they use in truck suspension systems, set the counterpoint right and they'll retain a ton of energy. I'm sure that there are other materials that could do it. Also do you just have to build it, or do you have to show the math behind it as well?

no math, just be able to launch it, the grading goes as follows. 60 feet= D, 80=C, 100=B, 120-how far we launch it =A. the record is set at 185. I really want to kill that record, so I'm trying to build one that can launch it at least 200 feet. right now I'm working on a all metal catapult, figured metal was the way to go.