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Flavorflav wrote:the arms of high-end compound bows are made if carbon fiber, which suggests to me that it must be very good indeed for energy storage.

Carbon fiber has some characteristics that make it appropriate for use as an elastic. Those characteristics may/or may not be used to advantage, depending on the design of the Trajectory device.

Virtually all materials are elastic to some extent. Carbon fiberhas a relatively higher modulus of elasticity than many other elastic materials. This makes it much stiffer and able to generate more force with less deformation, a property which makes it suitable for recurve/compound bows. In addition, it's lower density helps to reduce the overall weight of the device. Increased stiffness produces larger variations in the energy stored for any given error in intended deformation. This can cause unexpected/erratic results.

My partner and I are in the process of building a torsion powered catapult (a catapult powered by twisted rope). I THINK this is allowed, as does my coach... what do you guys think?

cheezwarrior12 wrote:My partner and I are in the process of building a torsion powered catapult (a catapult powered by twisted rope). I THINK this is allowed, as does my coach... what do you guys think?

Yes, it is allowed. Rope is a nonmetallic elastic solid. A torsion powered catapult is often called an onager.

Flavorflav wrote:

cheezwarrior12 wrote:My partner and I are in the process of building a torsion powered catapult (a catapult powered by twisted rope). I THINK this is allowed, as does my coach... what do you guys think?

Yes, it is allowed. Rope is a nonmetallic elastic solid. A torsion powered catapult is often called an onager.

Unless it looks like a bow, then it's a ballista

I really need some help. I have been trying to find something to launch the trajectory with. I tried bungee cords, and it was working well until it broke. I tried to buy more bungee cords from a dollar store, but they broke immediately when I tried to stretch them. I need something with a lot of tension that can withstand being stretched. Are bungee cords the best way to go, or is there something better?? Is there a specific length that works for bungee cords?

Fireheart347 wrote:I really need some help. I have been trying to find something to launch the trajectory with. I tried bungee cords, and it was working well until it broke. I tried to buy more bungee cords from a dollar store, but they broke immediately when I tried to stretch them. I need something with a lot of tension that can withstand being stretched. Are bungee cords the best way to go, or is there something better?? Is there a specific length that works for bungee cords?

maybe thats the problem...jk, ok so have you tried using surgical tubing or rubber bands, we used rubber bands at nationals and got 14th so don't under estimate their strength

Yeah, I'm thinking the fact you got them from a dollar store might have something to do with them breaking. Although you say they snapped immediately when you tried to stretch them? We've been using the same 2-foot-ish bungee cord for at least a year and it hasn't broken. Yet. Surgical tubing is also pretty good, but you want to make sure you get the good stuff (i.e. not from the dollar store, please). We haven't tried rubber bands, though, so I can't give any advice on that.

if you use rubber bands you will need a bag of about a hundred or so, this is because after a long term use the rubber bands will begin to stretch and remain that way. We usuallly stretched ours out before using them, which was the length from the trigger to the projectile.

cypressfalls_Robert wrote:

Fireheart347 wrote:I really need some help. I have been trying to find something to launch the trajectory with. I tried bungee cords, and it was working well until it broke. I tried to buy more bungee cords from a dollar store, but they broke immediately when I tried to stretch them. I need something with a lot of tension that can withstand being stretched. Are bungee cords the best way to go, or is there something better?? Is there a specific length that works for bungee cords?

maybe thats the problem...jk, ok so have you tried using surgical tubing or rubber bands, we used rubber bands at nationals and got 14th so don't under estimate their strength

I have tried exercise tubing, but I wasn't able to get enough tension for the projectile to travel far. Where do people typically get good surgical tubing (non-dollar-store types)?

Fireheart347 wrote:

cypressfalls_Robert wrote:

Fireheart347 wrote:I really need some help. I have been trying to find something to launch the trajectory with. I tried bungee cords, and it was working well until it broke. I tried to buy more bungee cords from a dollar store, but they broke immediately when I tried to stretch them. I need something with a lot of tension that can withstand being stretched. Are bungee cords the best way to go, or is there something better?? Is there a specific length that works for bungee cords?

maybe thats the problem...jk, ok so have you tried using surgical tubing or rubber bands, we used rubber bands at nationals and got 14th so don't under estimate their strength

I have tried exercise tubing, but I wasn't able to get enough tension for the projectile to travel far. Where do people typically get good surgical tubing (non-dollar-store types)?

Here or go to a sports store and get the excercise tubing with the most resistance you can find (or less depending on the design.)