I have a t-shirt launcher project that should not use compressed air/chemical reactions. I have considered the idea of a spring system but it seems getting the right spring length and strength will be difficult since I don't really know exactly how much energy a t-shirt will absorb with such a system. So my current hypothetical system mirrors a baseball pitching machine with two counter-rotating wheels.

My immediate concern is getting the proper motors for this machine. They should be relatively small (the device must be carried without support) high rpm, high torque and battery powered. My first thought was to buy a couple cordless angle grinders and use those motors but I'm concerned that the torque will be too low (I have experience with cheaper cordless grinders so not sure about the more expensive bosch/makita brands). The torque must be high or else the RPM's will drop too far to shoot the shirt the required 25ft.

Also, whatever kind of motor I get it should be able to handle the weight of a rubber tire as it spins. I'll be reimbursed for at least $100 for the project but I don't really have a problem with spending additional cash. In fact if I get the project done early enough I plan to modify it to be able to run remotely with a gravity fed magazine of t-shirt projectiles.

By the way, if anyone has an idea for a t-shirt cannon that doesn't involve any kind of gas I'm all ears. Really struggling to think of any other method that isn't in some way creative (catapult, balista.. crossbow seems too easy to me).

Thanks for any help!

 

To use the ball pitching idea you would need to put the shirts in some kind of capsule/container. The shirt would get caught in the mechanism other wise.

Instead of a spring, have you thought of bungee cords? Make something on the order of a spear gun, like scuba divers use.

 

Hello,

How about something mechanical, a catapult:
http://www.stormthecastle.com/catapult/the-goblin.htm

You can scale it up to your needs.

Bertus

 

A slingshot or crossbow?

 

Pretty much all of those ideas are taken now. There are actually two people doing crossbow-type contraptions now. I really want to make something that is set apart from the rest. And, whatever I make must be able to be carried by whomever is using it.

I'm allowed to roll and secure the shirt in whatever fashion I desire. Because of that I feel I can avoid the shirt getting caught up in the wheels pretty easily. I plan to cut a valley into the wheels where a piece of metal can rest that should help guard against the shirts getting sucked in.

I keep bouncing spring ideas in my head but I am just worried about how far I'll really get a shirt to go if it deforms too much from the initial force of the spring. I'll def. need to get a long, stiff, spring in that case. I suppose I could still use some kind of motor to compress the spring in that case. That would still require a very high torque motor that runs on battery.

Thanks again!

 

Angle grinders @ harbor freight for 15$. http://www.harborfreight.com/4-1-2-half-inch-angle-grinder-95578.html
I think the angle grinders will work just fine. Attach heavy solid steel wheels with plenty of inertia and I bet they would neve even know they had just launched a shirt, just keep on spinning at frightening speed. Might take a minute to get up to frightening speed though.
Swap the polarity of the field coil on one of them so that they spin opposite directions. On the one that's spinning backward, drill a hol throughout the wheel, through the threaded shaft, and put a spring pin through. Otherwise it will unscrew itself as soon as you turn it on.

I'm thinking a piece of PVC with 2 windows cut into it fir the wheels to stick throuhg. I think that should eliminate a lot of the risk of the shirts getting caught up.

This thing is going to be dangerous. I would test it first several times from a distance, and once I was confident in it, I still wouldn't use it without wearing a full faced motorcycle helmet.

 

Yeah, I planned on having both wheels 90% covered. I will be testing it a lot before bringing it in also. If possible I'll add sensors inside the casing that when blocked should cut power to both the wheels.

If it ends up being too dangerous ill do something else.

 

I think a key issue here might be how the shirt is packaged (set in concrete, probably against the rules ha ha). If you can roll it up into a dense cylinder, it'll be reasonably aerodynamic. Just loose, you have an obvious failure. I'd give a lot of attention to that issue.

 

Yeah, I will have to make it as solid as possible. Just not so solid that it hurts when it is caught..

 

Yeah, I will have to make it as solid as possible. Just not so solid that it hurts when it is caught..

Or possibly worse, not caught...

 

Sorry man, I dont see a spring having enough force to move a shirt.
potato gun would be cool but might ketch the shirt on fire.

 

Sorry man, I dont see a spring having enough force to move a shirt.
potato gun would be cool but might ketch the shirt on fire.

I think propellant are against the rules.

As a former dabbler in potato gunnery, I feel qualified to say that to achieve a proper design and proper hairspray load that would be powerful enough to reach its target, yet not powerful enough launch a t-shirt through a human torso would be tricky. Some sort of metering system would probably be necessary to ensure exact and repeatable stoichiometry in the combustion chamber.