Motor Step/Turn Mismatch with 3 Phase TMC389-EVAL

[tungyen_wu]

Hi all,

I am stuck at working with TMC389-EVAL board. 3-phase - 1.2°/Step running in Full-step mode means it takes 300 steps per rotation. However, when I hook up a 3-phase motor with the TMC389-EVAL board, it takes only 200 steps to perform a rotation.

Could anyone kindly provide some comments? Thanks in advance.

Regards, Ty

[TRINAMIC_BD]

Dear Ty,
this is in fact tricky: The 300 Step 3 phase motor has 50 electrical rotations per mechanical rotation. The TMC389 splits each electrical rotation in 1024, 512, ..., 8, 4 "microsteps". But, transferred to the three-phase motor, an electrical roatation is 6 fullsteps. Thus, when you set 256 microstep resolution, the resulting real microsteps is 2/3 of this value, e.g. 171 microsteps. At electrical fullstep it is 2/3 microsteps. This means, that with MRES=8, you get 1.5 steps of the motor - this is not true fullstepping. So, it is much better to work with higher resolutions.

[tungyen_wu]

Hi Mr. Dwersteg,

Thanks for your kindly support. However there are issues I don't quite understand.

Do you mean if I am using 3-phase motors with 300 microsteps in Full-step mode, I have to select higher resolution driver instead of TMC389 (300 microsteps)?
I can only use 1.8°/step, not 1.2°/step, correct?

Is there any method to achieve 300 microsteps for a 3-phase motor?

Also I have tried motors as SHENG FU (Taiwan), SAMSR (Japan) and JINGBO (China), all come out with the same results.

Thanks again for your kindly support
Regards, ty

[TRINAMIC_BD]

Dear Ty, concerning fullstepping, the conclusion of my post is just, that the TMC389 does not realize fullstepping when you switch it to the lowest resolution. It is more like 1.5 Fullsteps per pulse. A real fullstepping is not realized within TMC389 - the TMC389 is more intended for higher performance microstepping. Can't you work with microsteps?