General > General Technical Chat

Determining rotational accuracy of a drive unit.

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james_s:
The accuracy should be fairly constant though, a stepper motor is always going to move in discrete steps which are directly tied to the mechanical construction of the motor. It's not going to randomly take a different number of steps to make a full revolution.

Benta:

--- Quote from: james_s on May 21, 2021, 06:46:06 pm ---The accuracy should be fairly constant though, a stepper motor is always going to move in discrete steps which are directly tied to the mechanical construction of the motor. It's not going to randomly take a different number of steps to make a full revolution.

--- End quote ---

Quite, no dicussion on this.
But to take a (possible) resolution of 1/25000 and translate that to an angle accuracy of 0.0144 degrees (or whichever unit) is a very far leap.
The magnetic poles in the motor are not even machined to tolerances that would allow that kind of accuracy.

And then adding a worm mechanism on top of that for even higher resolution (not accuracy) is asking for trouble.


nctnico:
It could be the stepper motor has an internal reduction which then adds to the error as well.

Puffie40:

--- Quote from: nctnico on May 21, 2021, 08:56:17 pm ---It could be the stepper motor has an internal reduction which then adds to the error as well.

--- End quote ---
No, the stepper motor has no other reduction- it is a direct drive.  It's full step size appears to be 1.8 degrees, since its lowest resolution is 200steps/rev.

james_s:

--- Quote from: Benta on May 21, 2021, 07:53:41 pm ---Quite, no dicussion on this.
But to take a (possible) resolution of 1/25000 and translate that to an angle accuracy of 0.0144 degrees (or whichever unit) is a very far leap.
The magnetic poles in the motor are not even machined to tolerances that would allow that kind of accuracy.

And then adding a worm mechanism on top of that for even higher resolution (not accuracy) is asking for trouble.

--- End quote ---

Yeah 25,000 steps/rev is totally unrealistic I think, that just sounds like marketing wank to me. Microstepping can be useful to make a stepper operate more smoothly, but I would still not expect it to stop accurately at a point in between physical steps of the motor.

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