I would like to throw down a challenge for people to build their own "traditional" catapult (trebuchet) and then "compete" against others here to see who has built the best catapult in terms of historical accuracy, range, thrown weight (per scaled throwing arm length).

You can build them any size you like, from desk top hurlers to football field monsters. The choice is yours. Once you've built your catapult, field test them for maximum range and the thrown weight compared with "real" catapults. (You are responsible for local laws on firing projectiles in public!)

Gather 3 sets of results (in metric or imperial units only)
1. maximum range possible & the thrown weight used
2. maximum thrown weight and the range obtained
3. a third set of results somewhere in between the first two. Try and find the optimum balance between range and thrown weight.

Measure and report the length of throwing arm, length of counterweight lever arm (measured to c.g. of weight) and post your results and a picture of your machine here and I'll scale the results for you and compile them into a graph to see who's machine is the most effective. To enable a equal basis for comparison, I might scale directly all results to projectile weights close to the 100gms (0.1kg) range for starters. This of course is not really realistic since a direct upward or downward scaling of a catapult makes for some ridiculous sizes but for a simple comparison of throwing efficiency, I believe this should suffice.

To limit the range of types, choose only from three types of catapults (no wheels because wheels on hanging bucket catapults increase their range).

1. (Chinese) counterweight trebuchet (hanging bucket)
2. (Chinese) counterweight trebuchet (fixed weight)
3. Roman Mangonel


Go here for the Physics of a Trebuchet. It gives very good pointers on the various ratios required and the optimum lengths to go for when building a catapult.
http://www.geocities.com/SiliconValley/Park/6461/index2.html

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As a start, I'll use my little trebuchet as the challenge for anyone to beat. It shouldn't be too hard since I didn't build it for performance but more to look good.


Here are the stats for my trebuchet and the first benchmark to be beaten.

430mm throwing arm - 140mm counterweight lever arm.
1. 8.5m - 0.01kg (20mm diameter stone @ density 2400kg/m3 (concrete density))
2. *results pending*
3. *results pending*

Feel free to ask me for help if you need any info but half the fun is in researching the information to help you build your very own catapult.

Those based in Singapore are welcome to challenge my trebuchet directly. I'd gladly take you up and we can "match" catapults at a deserted section of Marina South or something.
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LET THE GAMES BEGIN!


*this graph at the moment is pretty meaningless since we only have one result from each of the two catapults and the values don't represent the optimum or maximum throw ranges of the catapult. I will update this chart when we have more values to compare with, (minimum three values- max possible projectile weight, max possible range and one value in between)

a catapult is different from a trebuchet, which one did you build?
a trebuchet uses counterweight centrifugal force; a catapult can use a spring and has much simpler design.

i built a catapult for school project a few years ago. it could launch 1 pound projectile over 30 meters at least, accurate within 1 cm.

Well... I had a physics class in which the teacher made us build a catapult...we built a ballista instead and still got away with it somehow with the grade of a 96...

One guy build a trechbut that's goes INCREDIBLY UNREASONABLY far. He shot it in a gym, and the ball touched the ceiling while it's STILL going upward. The ceiling is tall, but I don't know the exact height of it. It's like 4 stories.

Thanks for the clarification. The Catapult is the generic name for anything that "catapults" an object up into the air. I am referring to siege engines of the trebuchet varient though I'm reluctant to use the term trebuchet since this term is generic only to mean european (french) siege catapults.

I have more pictures of my trebuchet & a ballista I'm making posted in this thread.
http://www.chinahistoryforum.com/index.php?showtopic=3214

Ah Janz, do you still have that catapult? Any pictures?

ahh, i don;t think i took a picture of it. it wasn't a difficalt design, i built it with partner over one weekend. that thing couldn't fit in a car, we needed a van to move it. it was a few years ago, i can't remember the specifics.

i remember the catapult had a triangle base which supported a board. the board was attached to one or two spring(s) at one end. there was some sort fire mechanism(a metal rod or some sort which provented the catapult from launch) on another end. before fire, load up the catapult, put on the metal rod. when needed, just pull out the metal rod.
i just remember it had the longest range(double or triple other people's cats) and the best accuracy(most of them dependented on luck to hit any target) in that class.

a trebuchet should have a greater range, but i thought a trebuchet would have too many parts, thus easier to mess up.

hehehehe, well ok. Anyone here making a catapult to challenge?

This reminds me so much of 2nd year Mechanical Engineer ... *flash back* ... "No Johny! NOOOOOO! ... you Bastads ... YOU KILLED JOHNY!" ... *cold sweat*

Tip... make sure that your lever is as stiff as you can get it or else it will wobble

Make sure the stopper is well strong enough and superstiff.

Guess where my group made the mistake ?