What are some unique propulsion systems for a pinewood derby car project?

[ofinucan7]

Homework Statement

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Relevant Equations

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Hello all,

I am currently working on a project where I have to make a total of 3 pinewood derby esque cars. The rules of the project are pretty strict. First, the car must remain on the ground at all times. Second, the car must be self propelled. Third, the car must be able to go in a straight line. Fourth, the vehicle must fit in a 1'x2'x2' box. Fifth and finally, the vehicle must cost no more than $30. With all the restrictions out of the way, here is my project so far.

I have finished 2 of the 3 cars. For the first car, I wrote an arduino script that uses some sensors and for the second car, I used a gravity based propulsion system.

For the scoring of the project, I get point based on if the car worked or not and how unique the propulsion system is. I have put a decent amount of time into finding a third propulsion system, but I am not finding anything that I think will score very well. Any sort of idea would be greatly appreciated.

Thanks

 

[phinds]

Well, how about you tell us what you HAVE found so people won't make those suggestions?

 

[berkeman]

Welcome to the PF.

The rules of the project are pretty strict. First, the car must remain on the ground at all times. Second, the car must be self propelled. Third, the car must be able to go in a straight line. Fourth, the vehicle must fit in a 1'x2'x2' box. Fifth and finally, the vehicle must cost no more than $30.

There must be more goals and rules than that. Fastest car from point A to point B? Carry the most weight? Pull the heaviest load? These rules seem underconstrained to me, and what is the goal? How is the competition judged?

I'm inclined to use model rocket engines on this, depending on the rules. It's hard to beat their energy density...

 

[ofinucan7]

Mentioning what I have found would of been smart to being with. Obviously I have found your generic options such as the mouse trap and rubber band powered cars. I have also looked into something powered by a fan or some sort of propeller. I've experimented with the idea of using magnets, but I can't find a solid way to make it self propelled. Probably the most out there thing that I have found is a car powered by salt water. With my restraints of this project, a decent bit of what I have researched isn't applicable.

I also should of mentioned what the end goal was, my bad... Pretty much, I have to get the car to travel somewhere between 6-8 feet. The car doesn't need to hold anything or have any weight on it, but the only two stipulations are that I need to be able to pick the car up after it stops moving and that it needs to be consistent. That is that it needs to go that 6-8 feet every time I start it. The car doesn't need to go 100 mph, but at the same time, it needs to be able to move at a decent pace. As much as I would love to use a model rocket car, I don't know if it would be usable for my project.