Stepper Motor for Propulsion

[JackB]

Hello,
I was wondering how well a stepper motor might work for propulsion, or if it can be modified for that purpose.
I have a large 1.8 degree step motor, it is rated at 1.5hp.

Thanks, Jack

 

[Kingfish]

A good question to be sure.

The problem with a stepper motor is that there will be a tremendous amount of freewheel drag; you will always have to have power to allow the wheel to overcome the massive holding power of the magnets.

I am sure there are other viable reasons though I should think it is the primary reason.

The opposite analog of a stepper motor would be an ironless axial flux motor where there is very little measurable freewheel drag.

~KF

 

[SHARKBITEATTACK]

Is a stepper motor the same as a servo motor?

 

[Chalo]

Is a stepper motor the same as a servo motor?

No. A servomotor is a drive motor with a rotary encoder that provides a feedback loop.

A stepper is a motor designed expressly for motion control and not propulsion, which maintains step-by-step open-loop orientation control as long as it is never stalled. It uses about as much juice holding its position as it does when rotating (unless its controller is programmed to shut off power once position is established). To work correctly, a stepper motor must have more torque available than any normal load it is connected to. That makes it unsuited for traction applications.

 

[JackB]

Having taken apart my stepper motor, it is basically just a sensorless brushless dc motor, 2 phase.
Being a 1.8 degree step, it has fine and offset "fingers" on the laminations to line up at 1.8 degree offsets.

So I take it nobody here has tried to run one at rpm like a normal motor?
It would seem to have smoother low-rpm torque than a traditional bldc motor that is more like a 60-degree "step" motor.

 

[Kingfish]

Why don't you give it a shot and tell us how it goes. I suspect it will not spin very fast, though probably have enough torque to pull the Moon.

~KF

 

[neptronix]

common 3 phase motors we use don't move in 60 degree increments

You're going to have a hard time finding a 2 phase controller that can do what you want, unless you want to modify an existing one for this duty. But i don't think you're barking up the right tree here.