How can I change torque, like the motion generated by an electric motor, to a linear force, like the force generated by a linear motor? What kind of device would do this? The motion should be piston-like.

Okay, let me elaborate more:

I'm building a Beta Stirling Engine that will act like a cooler. I will run it using another Stirling Engine, and the torque will be applied on the flywheel of the cooler. The drive mechanism is too complex. I was wondering if there is simply a way to convert a wheel's motion into a linear force WITHOUT any angular or side motions. I should attach a drive mechanism to the wheel, and I want the end of the drive mechanism to have no side motions, only linear motions like that of a piston.

Thanks.

You should ask this in the engineering forum.

Yeah probably. The thing is, the focus is not primarily on the engine, but on a mechanism that changes the torque generated to linear force. Thus I couldn't decide whether it was engineering or physics.

Err...moderators and admins can probably move this to engineering if you see fit.

You could either create the reverse of what is on a steam trains wheels which would give you a backwards and forwards motion, or have a cog on the end of the motor which turns a screw moving it in a certain direction. Allthough in reality I suspect it would be more complicated than just a cog and screw obv..

You could use a piston but backwards. a piston used ormally turn linear force into torque so it you apply a torque to output you'll get a linear force from the piston.

Yes, a piston would work. However, this is a rather special case with mine. I have two pistons aligned in a line inside the same cylinder. The rods connecting them to the crankwheel are separated by a 90 degrees angle, so the 2 pistons don't move uniformly up and down. I have to connect the rod of the upper piston to the crankwheel THROUGH the second piston, but the sideways motion of the rods resulting from the crankwheel spinning complicates matters, because any sideways motion of the rod would make a perfect seal of the piston and cylinder difficult.

Here are 2 pictures of what I'm talking about:

http://www.geo.unizh.ch/~iwoodh/beta1.gif

http://www.keveney.com/img/stirling.gif

Never mind, I got it. Thanks everyone.