Rubber Band Propeller. Suggestions?

zeronos · Post by **zeronos** » Sun Sep 23, 2007 2:15 pm

Hi everyone, this is my first time posting around here.

I'm building the common self propelled car project. My current source of power right now is using rubber bands to twist the axels of the car. However, I am near finished and have some extra time (a couple weeks, to be precise), so I am interested in adding a little extra power to my vehicle.

Anyone know of an effective way to attach and perhaps construct a propeller powered by rubber bands? Power and longevity of the propeller would be most appreciated. If this helps, the body of the car is similar to that of a 2 liter soda bottle.

Thanks in advance.

zeronos · Post by **zeronos** » Sun Sep 23, 2007 2:17 pm

I'm sorry for posting twice in a row.

In addition, I am seeking a goal of 75 meters for my car. Right now, it's averaging about 50-60 meters.

Craig_Bridge · Post by **Craig_Bridge** » Mon Sep 24, 2007 7:53 pm

How much does your "car" weigh (or what is its mass)?

Even the best propellers aren't very efficient propulsion systems so unless you have an extremely light vehicle, you might do better at refining your existing design.

Is there any way to shave off any more weight without loosing structural integrity? This will probably have the biggest payoff.

Is there a way to increase traction if there is any initial spining of the wheels? If you are spinning your wheels at the start, this will be another big payoff.

Is there a way to increase the power supplied by the rubber bands?

Is there a way to decrease friction of the bearing surfaces?

Is there a way to decrease drag by making the design more aerodynamic?

zeronos · Post by **zeronos** » Mon Sep 24, 2007 9:08 pm

Uh, my new car is about 110 grams, made mostly of plastic.

I am willing to change my design to propeller only for 60 meters, if it works out

The top half of my car is reattachable, so it will be about 60 to 50 grams then.

I'm sorry, but I don't understand the question. I have ridged lids for wheels, if that helps.

Is there a way to increase the power supplied by the rubber bands? I can't think of a way.

Not really, it's just tile.

It's shaped more like a missle than a car, actually.

Thanks for answering.

Craig_Bridge · Post by **Craig_Bridge** » Tue Sep 25, 2007 1:42 pm

Is there a way to increase traction if there is any initial spining of the wheels?

I'm sorry, but I don't understand the question. I have ridged lids for wheels, if that helps.

Is there a way to decrease friction of the bearing surfaces?

Not really, it's just tile.

Sorry, I was probably using some technical words that you aren't familiar with. This is one reason why we ask what grade you are in so we can pick appropriate ways to word things.

Traction is a friction like property that allows the wheels to not spin or slip on the surface as they start. I'm guessing that you have plastic lids with rims and are starting on a tile floor surface. On way to detect slippage would be to us a marker to put a big mark on the wheel where it contracts the tile at the starting point and see where the car is when the mark on the wheel is down again after making one revolution. If the car hasn't traveled as far as it should have, then there is slippage. On way to reduce any slippage and increase traction might be to place wide rubber bands around the lid like a tire tread.

I also used the word "bearing" which is a fancy name for something that holds an object in some way while still allowing it to move in another way. Somehow the axles and/or wheels are being allowed to rotate while they are still attached to your car. Whatever it is that allows this rotation is the "bearing". Are the surfaces of the bearing and the axle smooth? If not, is there a way to polish them? Have you tried a small amount of some lubricant (if that is allowed)? These are typical ways of decreasing bearing friction.

As far as increasing the force out of the rubber bands, can you add another rubber band into the twist?