Stepper motor question.

[JBajkor]

What do you guys think about putting 2 identical stepper motors in parallel? They would be installed one on each end of the drive screw, physically in phase and electrically in parallel. Should work, see any problems?

[MikeSherman]

I don't have personal experience doing that, but I don't think that set-up will play well together. The two motors will fight one another. Nothing is ever "exactly the same" and if they are holding position or making a move, each motor will do it's thing slightly different.

Either get a larger, stronger single stepper or gear down the smaller one you have if speed isn't an issue.

-Mike

[JBajkor]

Thanks for the reply.
Just ordered a pair of 850 oz-in motors so no need to parallel my small ones.

[wacojoe]

Should work fine. There are a lot of 3D printers using 2 stepper motors driving a screw/threaded rods on the Z axis. Although they are not attached to the same screw, but they should step the same amount each time.

For whats its worth, the ones on my printer do not go out of phase.

[Grimmy]

You're talking a master/slave setup. I see this a lot at work. I'm an electrician and I work on the cnc machines at work to try to keep them going. Parallel won't work, cause if you have one motor on a screw on one end, and then another motor on the other end of the same screw, one motor has to turn backwards or mirrored. With a stepper motor, you might be able to. I don't know how accurate the positioning is on stepper motors, but the motors we use, have a million pulse encoders on them, so 1 million pulses per revolution. Plus we have incremental glass scales on those axis as well.

Can it be done, I'm sure it can, but you have to or should wire it and configure it as another axis, just mirror it. That done with a parameter on a Fanuc control.

Hope that helps.

[JBajkor]

Good info guys. I like the idea of 2 screws. My original plan was using a couple of 270 oz-in motors. No problem making one go backward, just a matter of reversing A and B wires.
However, now that I have 850 oz-in motors coming, one on each axis is plenty.

[Grimmy]

While that might with with stepper motors, anything with an encoder on the motor though, it wouldn't work, as the encoder will tell the control it's going the wrong way, therefore you need to tell the control to mirror or reverse the motor. Typically when they are wired wrongly don't don't match the encoder, the axis or motor will run away as fast as it can. The older equipment that I used to work on, that's how they worked. The newer stuff, well most run glass scales for super accurate positioning.

[JBajkor]

I understand the runaway you talk about. Feedback must also be reversed or you get the same thing as setting your tail gyro sense wrong. However, mine is a simple open loop system.