Suppose I have a small stepper motor, and for reasons (like wiring considerations) it is advantageous for me to not actually have the motor's body fixed as the shaft rotates, but rather have the shaft fixed in place while the entire mechanism of the motor rotate around the shaft. Are the two schemes equivalent if we assume that the shaft is perpendicular to the ground? My ultimate case is to have a stepper motor rotate while it is upside down, without using additional gear wheels or any other component other than a coupler which secures the shaft to a solid base.


Are the two schemes equivalent?

Mostly so. Usually the motor is affixed to a sturdy chassis resting on a solid surface, sinking vast majority of vibrations and jerk coming from the motion. In your configuration, both the motor and anything attached to it will be fully exposed to these vibrations - which introduce all kinds of headaches like electric connectors losing contact, wear of joints from material fatigue, screws coming loose, and so on and so forth - not a single thing critical, just a mountain of small headaches. You're also dealing with accelerations in case the element turns fast (and especially if it stops rapidly, say, knocking against a brake), and you have to get power and control to the rotating part somehow. Control is fairly easy using short-range wireless communication like bluetooth or IRDA. Power is worse - you'll either limit your angle so that an attached cable doesn't get too twisted, or supply power through batteries. Or you can use a slip-ring for both power and data, but slip-rings are another can of worms, something that works okay in 'big industrial', but on small scale is so fault-prone and quirky you're better off redesigning everything to have a fixed stepper.

  • $\begingroup$ My initial intention was to solve the problem of a limited angle, which is introduced if I use a traditional approach ( like adding more moving parts, gearwheels, etc). The motor will never spin very fast, and the plan is to use a battery which sits on the inside of the system and spin along with everything else ( as well as the controller) Your post actually was helpfull as there were issues I was not aware of, thanks. $\endgroup$
    – dvd280
    Nov 26 '20 at 11:36
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    $\begingroup$ Note even with low speed, unlike DC motor, stepper inherently produces vibrations, a jerky motion - the steps are practically never in sync with torque / angular acceleration so instead of smooth rotary motion you have a lot of acceleration and braking as the motor heads to the next 'step' and then starts stopping there before control forwards the motion to the next step. Batteries exposed to this sort of treatment dance in their compartment easily losing contact with the contact springs. Also you definitely should have some means of 'emergency stop' in case of communication failure. $\endgroup$
    – SF.
    Nov 26 '20 at 12:10

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