School Project: Gravity Car Design

Hey there guys... In my physics class we have a project in which we have to make a gravity-powered vehicle that will carry a given load along a track. The vehicle can only be powered by gravity (weights) and cannot use any other energy source such as elastics, springs, explosives, etc. I have started to make a K'nex vehicle but it is not very sturdy. The following is a picture of the rules and specifications. Much help is appreciated. Thanks

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PKM9 years ago
Tell you what- to give me time to fix the wording of my objection to this principle in my head rather than posting some incoherent ramble, why don't you post a quick photo or video of your working prototype. You do have a working prototype, don't you? A simple video of it on a flat tabletop, with a spirit level or something in the background (could be just a glass of water) to demonstrate that the tabletop is level, rolling from a standstill under just its own power will be more than sufficient. Oh, and you say "This is the very first design in existence whereas the weight moves with the car yet stays in the forward quadrant of the hollow back wheel.". Oddly enough I had this same idea years ago...
PKM9 years ago
Hate to tell you this but these are ancient and well-known perpetual motion designs. The constantly off-balance wheel is an attractive design for perpetual motion but it is impossible. A weight has to fall to do any work, simply holding a weight over the front part of a hollow wheel will not make it rotate.
guyfrom7up PKM9 years ago
Bah!! That's what you and your physics say, but it has yet to be done! It use to be considered impossible to fly
PKM guyfrom7up9 years ago
Please, please tell me that was irony and you omitted the ":P" from the end.

In case it wasn't, "It use to be considered impossible to fly" was an engineering challenge, not an unbreakable law of nature. Anyone who thought it was impossible to fly was clearly very stupid, because there were these little things with feathers on that had been doing it for a long time. A weight can only do work (note: not exert a force, the two are different) by falling. No ifs, no buts.
Aar000n3y9 years ago
For going up to 1,000 grams, I don't think KNex are strong enough... I think it would be better to just use a stronger material. Also, you should really use much bigger wheels (the ones that will be powered at least). Because one turn from a large wheel would make the car go farther than one turn with a smaller wheel.
jtobako9 years ago
Well, puberty hits some later than others... Actually, think "rack and pinion" in a car-the pinion is a small, round gear which leaves the long, flat gear as the rack.
RaDiKaL (author) 9 years ago
He said the device needs to move as one. :P guess i cant do it
RaDiKaL (author) 9 years ago
After 2 hours of work I have finally finished a prototype. I made it using K'Nex. I still have to add a smooth surface for the ramp on top (Any ideas of something light, smooth, and sturdy?). The very front wheel starts in a retracted position but when as the weight goes down the ramp the wheel lowers until it hits the ground giving it more support.
For a light smooth surface I recommend Masonite. it's very commonly available and very smooth. It may be too heavy though, and if worse comes to worse I would just use a thin cardboard or plastic.
RaDiKaL (author)  Firebert0109 years ago
Any ideas for a lube? :)
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