Stepper Motor A4988 home state and home position

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alan70

Joined Oct 31, 2021
9
I have 2 questions concerning the datasheet for the Allegro A4988 DMOS Microstepping Driver which includes information on “home state” and “home position”.

My interpretation of these terms is:

“home state” is the combination of current requirements that need to be passed to the two phases of the motor to move the rotor to a “home position”.

A “home position” is a stable point and starting point for a 4 step cycle which will end at another stable point. The 50 toothed structure around the rotor leads to 50 of these stable points. Turning the shaft of an unpowered stepper motor will have a notched feel as the stable points are met and passed.

Question 1. For brevity I have greatly simplified the process but in general is my understanding of the two terms correct?

Question 2. Does home state vary with microstep resolution?

Many web sites dealing with the A4988 are cut and paste jobs of some original document which I have not yet found. One paragraph common to them says “Home state is basically the initial position from which the motor starts, and it varies based on microstep resolution.”

My understanding as given above is that home state is the set of conditions that need to be met to set the rotor to a home position, it does not vary based on microstep resolution.

On a Texas Instrument forum one of their engineers posted with regard to the TI DRV8811 driver “The device starts at the same point regardless of the microstep setting. It is referred to as the home state and is the 45 degree electrical angle. Full step, half step, quarter step and eighth step all start here.

Testing with my own setup (NEMA17/A4988) results tie in with what the TI engineer said.

Thanks for any help anyone can give.
 
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