Hi all, I've been reading about stepper motors and need some help to understand some of the specs and how to choose the step motor that is best for my application. 1- What is the difference btw Detent torque and Holding torque ? Which one is of more importance? 2- I need to get two step motors for my robot (as wheels). The robot is about 3-4 lbs. I don't need it to go fast, but i want the step motors to be strong enough to move the robot. I think a reasonable voltage is btw 9-12v. I don't want to use more than 12 v. I'm not sure about the Amps i found step motors with 40 mA, 80 mA, 500 mA, ..etc. How do I know what Amps is best for me? Also what type and value for torque will i be needing ( 200 g-cm, 400 g-cm, 1000 g-cm, ...)? 3- I've read about Unipolar and Bipolar. What is the major difference btw them? what things can I do with one that i cannot do with the other? Which one is easier to use? thanks in advance
1- What is the difference btw Detent torque and Holding torque ? Which one OK, I'll guess on this one... someone will correct me if I'm wrong... detent torque is with coils off, and holding torque is with coils energized? Get a fishin scale and see how many pounds you need to pull it at the speed you want. Torque is this force x the wheel diam (adjust units from SI to English as required...) I always get these confused... unipolar has 2 centertapped coils (6 wires) and you hook the centertaps to the batt and step the coils with transistors. Bipolar has 4 wires... 2 coils... and you energize them with either an H-bridge (one side goes up to +v, the other goes down to gnd), or +-volt supplies. The 1st type only has half a coil energized, 2nd type has the whole coil energized.. more torque, but more complex drive. 1st type can 'half step' though, doubling the steps. Tradeoff.
It does seem counter-intuitive, with the "uni-" having more wires and more individually-addressable windings. What worked for me was to silently replace the -polar with -directional, since during operation the current goes two directions in each bipolar winding but only one direction in each unipolar. Nothing to say that you can't step with two coils in a unipolar setup; instead of A - !B - !A - B, one would use A/B - B/!A - !A/!B - !B/A.
