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From earlier on this page, the axle diameter has nothing to do with the torque. Wheel size and the size of the attachment of the thread from the kill bar to the axle are the important things.The last time this event was run, I increased the axle size where the thread attached by gluing a piece of brass tubing (or nested tubing) We drilled a hole in the axle, put in a tight fit pin and cut that to a workable length.
On one, we had a home made triple pulley with a gradient to give high starting torque and a fast final speed. Winding it was not much fun.

With your 3D printer, you can program it to make trusses like those for metal roofs, or you can have it make holes to lighten the weight.

I still have a preference for hard balsa or light basswood or similar. Weight is a killer since the traps only give a given amount of torque (work).
If you are good at gluing you might use a frame and then kevlar (aramid) (Spider wire from Lowes) for a truss work. A good design and good gluing will give a fairly strong car.

retired1 wrote:From earlier on this page, the axle diameter has nothing to do with the torque. Wheel size and the size of the attachment of the thread from the kill bar to the axle are the important things.The last time this event was run, I increased the axle size where the thread attached by gluing a piece of brass tubing (or nested tubing) We drilled a hole in the axle, put in a tight fit pin and cut that to a workable length.
On one, we had a home made triple pulley with a gradient to give high starting torque and a fast final speed. Winding it was not much fun.

Doesn't torque change with the ratio between wheel size and axles size?

What's a "triple pulley with the gradient?" ( I know what a triple pulley is, buy not what a gradient is)

PM2017 wrote:

retired1 wrote:From earlier on this page, the axle diameter has nothing to do with the torque. Wheel size and the size of the attachment of the thread from the kill bar to the axle are the important things.The last time this event was run, I increased the axle size where the thread attached by gluing a piece of brass tubing (or nested tubing) We drilled a hole in the axle, put in a tight fit pin and cut that to a workable length.
On one, we had a home made triple pulley with a gradient to give high starting torque and a fast final speed. Winding it was not much fun.

Doesn't torque change with the ratio between wheel size and axles size?

What's a "triple pulley with the gradient?" ( I know what a triple pulley is, buy not what a gradient is)

I imagine that retired1 is referring to “gearing” an axle, where certain parts are thicker than others.

How have people been overcoming having the string wrapping back around the axle once it runs out of string and the car is rolling on momentum? Have people just used so much string/such a long dowel rod/big wheels that the string never runs out before the braking mechanism engages at the target line? Our car is really small, so to go the max distance of 7 meters (3 forward from the start line and 4 back from the start line) we cannot attach our string to our rear axle permanently otherwise it will wrap back around the axle and act as a brake. Has anyone else experienced this problem?

19sawickin wrote:How have people been overcoming having the string wrapping back around the axle once it runs out of string and the car is rolling on momentum? Have people just used so much string/such a long dowel rod/big wheels that the string never runs out before the braking mechanism engages at the target line? Our car is really small, so to go the max distance of 7 meters (3 forward from the start line and 4 back from the start line) we cannot attach our string to our rear axle permanently otherwise it will wrap back around the axle and act as a brake. Has anyone else experienced this problem?

Just don't attach it permanently, let it fall off once it's completely unwound.

19sawickin wrote:How have people been overcoming having the string wrapping back around the axle once it runs out of string and the car is rolling on momentum? Have people just used so much string/such a long dowel rod/big wheels that the string never runs out before the braking mechanism engages at the target line? Our car is really small, so to go the max distance of 7 meters (3 forward from the start line and 4 back from the start line) we cannot attach our string to our rear axle permanently otherwise it will wrap back around the axle and act as a brake. Has anyone else experienced this problem?

You should really try to get a system in which the string is long enough.
If you want to keep your current system, when you wind the string, just don't tie it to the axle, so that when it does unwind, it simply slips of the axle.

Does anyone have a system of using two mousetraps pulling the car in different directions that does not result in both mousetraps conflicting with each other? Our team is trying to find a simple method of doing this that will make the winding process easier with both mousetraps.

thesenotes wrote:Does anyone have a system of using two mousetraps pulling the car in different directions that does not result in both mousetraps conflicting with each other? Our team is trying to find a simple method of doing this that will make the winding process easier with both mousetraps.

I believe the most common process is to have both mousetraps pulling together and to simply wrap the string around the axle in one direction, then part of the way through wrap it in another direction.

For what you’re describing you could have a piece of metal sticking out of the side of the lever arm of your forward mousetrap so that when it snaps it pushes down on and triggers the backward mousetrap. But I think in general it’s better to use the other method I described.

thesenotes wrote:Does anyone have a system of using two mousetraps pulling the car in different directions that does not result in both mousetraps conflicting with each other? Our team is trying to find a simple method of doing this that will make the winding process easier with both mousetraps.

https://youtu.be/Br-Z88a9Ypg