Can Motors with Different AMP Draws be Mixed in One Machine?

Sorry, I think this is a very basic question but one I haven't found an answer to yet.

I was thinking of using this motor (17HS19-1684S) for all but the extruder on the X carriage. And I thought to use this motor (17HS15-0404S) as the extruder motor because it is considerably lighter. But it draws 0.4A while other motor draws 1.68A. Can these two motors be run at the same time off the same RAMPS. 1.4? And if they could, is a motor with 40Ncm (56.7oz.in) holding torque strong enough to turn a Wades small gear which turns the big Wades gear?

Thanks for any help

Unlike a dc motor, the stepper motor does not "draw" any amount of current it wants. It only receives the current that the driver gives. So that rating is more of a maximum, and the effective current drawn is the one you set on the stepper driver potentiometer by hand. The 0.4A motor is the wrong motor type, avoid it if possible (high inductance low current types). If you already have it you could try use it, but it will probably perform poorly. For the best use 1.68A type for all axes if you have the choice.

Edited 1 time(s). Last edit at 06/14/2014 10:40PM by NoobMan.

Aha! Thank you NoobMan! I'm getting it.

I have not bought the motors yet so I looked for different ones. I found a larger and a smaller motor from the same company both rated 1.68A

Larger Motor

- Motor length: 48mm
- Rated voltage: 2.8V
- Current/phase: 1.68A
- Resistance/phase: 1.65Ω
- Inductance/phase: 2.8mH
- Holding torque: 4.4kg.cm
- Mass: 0.35kg

Smaller Motor

- Motor length: 40mm
- Rated voltage: 2.8V
- Current/phase: 1.68A
- Resistance/phase: 1.65Ω
- Inductance/phase: 3.2mH
- Holding torque: 3.6kg.cm
- Mass: 0.28kg

Aside from size (and thus torque) they have identical specs EXCEPT the inductance/phase. The larger one is 3.2mH and the smaller is 2.8mH. Will that stop the two motors from being working together in one machine? Driven by the same stepper drivers?

I'm hoping so since I'd really like to use a smaller/lighter motor for the extruder. The smaller one has only 18% less holding torque and I am assuming that it will still drive the gears adequately.

Thanks again

Yes those motors are the correct type (high current low inductance). Other than that, the X and Y motors should be same model. Also if its a machine with dual Z motors, then those should match to each other. But other than that, Z could be slightly different than x and y. And at last, E could again be different from all the above, probably if you use a direct drive extruder you want high torque for e. If you have geared extruder, then motor could be smaller because the gears will increase the torque.

For a machine with independent x and y, like a moving bed, there is a moving assembly on x and another moving assembly on y. Only the one with higher mass counts for getting benefits via weight reduction. E.g. i dont know what is your situation, you should probably try to evaluate which of your axes weights more, the bed or the extruder carriage. If the bed weights more, a further weight reduction on x carriage does not bring benefits. If the bed is lighter than the x carriage (incl extruder), then it is the case that lighter x would be beneficial.

Great information - thank you!

The machine is in the design stage and I'm not yet able to make the final weight calculations for the X and Y axes. I am trying to balance their weights as much as possible. If there is little weight benefit from using the smaller motor on the extruder the machine will still benefit from the shorter motor depth.

It's a modified Wades style geared extruder so torque from the smaller motor should be OK. All motors except the extruder will be the same. Just the extruder motor will be a smaller size.

I will order these motors.

Thanks again,


Garry