# Coffee Can Racers!

Posted:
edited January 2014
In my physics class the first project we are doing is to build 'racers' that are powered by rubber bands and the object it to see how far you can get it to go.

I just have a few questions as they said we are allowed to get the help of anyone and I know that there are some smarter folks then myself around here.

I basically have decided that I have two options and would like to know which I have a better chance with.

1st-------------

Making it with as little friction as possible...probably CD's as wheels and a thinner longer running rubber band. Light weight as possible.

2nd------------

Making it heavy with momentum. I figure I'd put something for grip along the wheels so it doesn't spin out and use a thick and powerful rubber band. Place water bags inside and let the rubber band get the momentum going and hope it keeps it going.

Basically the requirements are that it has to be powered with a rubber band and be a standard sized coffee can.

So, any takers on giving me help?

Edit: If you want/need to see the paper explaining it I will scan it and provide a link.

Posts: 4,695member
It's a balancing act... too much mass, and you'll lose a lot of energy to friction in your wheel bearings, and to friction between your wheels and the ground. Too low a mass, and you may lose a lot of energy to slippage of your drive wheel(s).

I'd go for just enough weight to ensure a low-slip transfer of energy through the wheels. I'd also make a racer with an aerodynamic shape, because you have nothing to gain from air resistance.

You might want to consider some sort of simple gearing to release your rubber band's energy slowly. Since you want to maximize distance, not speed, I believe (you should research this to be sure I'm not full of it!) that for a given distance travelled, if you travel that distance more slowly you'll lose less energy to friction than you would at a higher speed.

This is all about an energy budget: Your rubber band gives you only so much energy. Your racer stops moving as soon as friction from various sources has turned all of your rubber band's energy into heat.
Posts: 5,012member
Hmm...I guess it's not worth it to create gears for this project, I'll save that for the rat-trap powered cars later this year in transportation technology.

I guess I'll use multiple rubber bands and hope to find a way to have it release more slowly. I guess maybe not put in the time to make the water bags for it then considering that might not even help \
Posts: 6,523member
The "I fell lucky" hit on Google with rubber band car. You young people are suppose to be superior to us old (25+) in using the internet. Guess not.
Posts: 5,012member
Quote:

Originally posted by Anders

The "I fell lucky" hit on Google with rubber band car. You young people are suppose to be superior to us old (25+) in using the internet. Guess not.

Not the kind of rubber band car I was talking about. It's basically a cylinder on its side that rolls on two wheels (sides of the can)

And I never ever use the "I'm feeling lucky" buttons at google.
Posts: 3,325member
any other limitations on materials?

# and type of rubber bands?

surface of track and conditions (hallway, grooved tiles to overcome, slick) ?

get a balsawood plane with rubber band prop.

build a mix of gears to drive wheels, using its own stiffer band if you want,

but i'd keep the prop and plane body mounted in the can for air-boat action.

cut out the can bottom put a tapered paper cone on the "back" and you'll have a "jet"

/ /-------------body of can------------\\ aerodynamic nose\\

cone .... prop and balsa plane fuselage .... open

\\ \\--super efficient (min friction) wheels---/ /