Multiple Steppers on Z axis

On the RepStrap that Im designing Im thinking of using 2 maybe 4 of the smaller Nema 17 stepper motors for the Z axis.

I will also be testing an idea of the bed being supported by the timing belts (4 of them, with guides to keep the bed stationary.

I would like to use all of the generation 3 electronics.

My question is with the RepRap Motherboard will I be able to run 2-4 Stepper motors off of the same motherboard output (with the outputs for the x and y axis's still free obviously)? If so would i just branch each connection to a stepper driver? If that Is not an option what other options are there?

I could always use one stepper to get it work the way im shooting for, but two would greatly simplify it.

Another Answer to my solution could be to use a stronger stepper, that will probaly use more current, can the current stepper drivers be reconfigured to handle a larger load?

Or can an production stepper driver be compatible with the RepRap Mother board?

I look forward to your responses.



Jeff Ballard

I think the gen3 stepper driver is limited to 2A. You could wire all four motors in parallel and they would get a maximum of 0.5A each.

That is certainly enough for a screw drive, see [hydraraptor.blogspot.com] and [hydraraptor.blogspot.com].

I doubt it would be enough torque to lift the bed with a belt drive unless you used counter weights.

There is no easy way to increase the current above 2A. That is about the point where you switch from a single chip solution to a driver chip plus discrete transistors.

The motherboard outputs step and direction signals, so yes you can substitute an off the shelf driver board from the CNC world.

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[www.hydraraptor.blogspot.com]

So a driver such as this one: Ebay Item number: 220401566239 would be compatible with the Gen 3 Motherboard, with the correct Supply voltage.

what is your opinion on this driver?

Yes that looks like it will do the job. You may have to tweak the firmware to satisfy the timing requirements. Drivers with opto coupled inputs tend to need longer pulse than an direct connection.

It is still only 4A so 1A per motor. The NEMA17's I have are 2.5A per coil so you would still be under driving them.

Sorry I miss read your original question. Yes you could wire several stepper controllers in parallel, and connect one to each motor.

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[www.hydraraptor.blogspot.com]

"Sorry I miss read your original question. Yes you could wire several stepper controllers in parallel, and connect one to each motor."

Would this be viable? For lets say 2-4 motors driven each by its own driver, and with each driver connected to the Motherboard Z output?

That is what id rather do.

Yes the step and direction inputs of the gen3 driver boards take next to no current so you can wire many in parallel. They will all step together.

You could start with two driving two motors each and if that is not enough go to four driving one motor each.

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[www.hydraraptor.blogspot.com]

Thank you very much. Im still in the design process for my repstrap, and i didnt want to head in a direction that wouldnt be easily supported.

I appreciate your help.

Jeff Ballard

One thing to bear in mind is how you synchronise the starting position of the four motors.

With my four screw drives I manually align them once and then they stay in sync because the motors don't move when I turn the machine off.

If you have the table hanging on belts it will drop when the power is off unless it is counter balanced.

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[www.hydraraptor.blogspot.com]