[balsaman]

Here is the formula:

Figure out how fast you want to go.

Figure out the rpm of the motor.

Figure out what gear ratio it takes to make your machine go it's max speed close to the motors max rmp.

Make sure your motors have enough torque to achieve this.

So, if your motors go 1000 rpm, and you want to go 100" per minute, you need a 10 tpi screw if you go 1:1 ratio (no belt). If your motors are 2000 rpm, you need a 2:1 ratio, or 4:1 if you use a 5 tpi screw.

If you have a rack and pinion, and the circumference of the gear is 3" (~1" diameter), then your motor would need to turn 33 rpm to go 100" per minute. Not very effecient use of your 1000 rpm motor, as it can't develop the hp at that low a speed.

Eric