Derby Talk

Hey. I have a simmilar project for my HS physics class... I need to design "self-propelled" car that travels @ least 5m... (the catch is that the car must be axle-driven!) So i am planning to use a 12g C02 tank, somehow fitted into a wood block, and have it aimed at a turbine geared to the axel. Heres my dilema: How to "pop" open the canister without touching it... I though that i could posssibly put a capacitior wired to a pile of magnesium shreads infront of the nozzle. When the capacitor connects, it will ignite the magnesium, and hopefully break the little tip? Any other ideas would be MUCH appreciated! Thanks, Mike.

If you are allowed battery powered electric motors, that could be simplest. Consider "pushing and/or pulling with a light beam." That is, control the motor from fore and/or aft photocells actuated by a flashlight.

If the motor is reversible, then you can "push it either direction."

Hmmm... then if you can make it steerable, mount two photocells in the front, angled 10 or 20 degrees horizontally, and steer toward equalizing light intensity on each.

Unfortunately, im not allowed electric motors... but im pretty sure i can use somedevice to open the cartridge....

I wouldn't use magnesium. If any of that burning material gets on the track, it will damage it.

For CO2 racing they use some type of mechanism that will puncture the cartridges. Try checking out the Pitsco website. http://www.pitsco.com/Resources/dragster.asp

The neat thing is is that this is not on a track. Its one of those "build a self-propllled car" projects... We'll most likely end up puting it outside on the cross-country track. And the magnesium would be a very small amount, just enough to puncture the seal on the canister? Im not sure how much heat/force it will take to rupture the canister.... I figure since the speed that the C02 will exit (~ Mach 1 according to a physics gurue site) will be enough to literally supercool anything next to it!

If you have a different idea for the canister rupture, please share it! I really appreciate your help!

I think you'd have better luck with a mechanical device that punctures the cartridge.

By chance, you wouldnt happen to know how much force must be exherted to puncture it would you?

Nope, sorry. The Pitsco website is a great resource. You might be able to find that answer there. Otherwise, time do some experiments.

We just had our first ever CO2 dragster race for our pack. The Pitsco starter punctures the cartridge with a pin leaving a hole about a 1/16” in diameter. The starter is spring operated and activated by an electronic starting device. The gas is expelled very quickly. You can see the vapor trail behind the cars for the first 8-10’ after that the car is a coaster. The faster cars of the day took just under 1 second to travel the 65’ course. (That is an average of 45-55 MPH). We ran a couple of non pack cars that ran in the 0.82-0.85 second range (average speed close to 80MPH). Given that average speed and the fact the cartridge is empty after the first 8-10’ you would have to capture all the energy from the cartridge in under 0.1 seconds in your turbine and transfer it to the axles and wheels during that time after that you are coasting.

The boys had a great time. We built the cars from a purchased kit and made it a parent-scout project in the same spirit of the PWD. Our pack will probably make this an annual fall event.

Hey - Thanks for the ideas.... Well. In that case, Ill fake it that the turbine is powering the axels, and focus on the expelling of the gas.

One idea - Mabe make two trails carvved in the wood (Really thin) to slow down the time the gas is released, and increase the pressure?

I thought of another idea..... The tube from a bicycle tire..... Those can be easily inflated to around 60psi, and are easy to deplete the air from.... THen just use tubing aimed at the turbine.... How would this compare to a 12g C02 canister?