Motors not Spinning at Low Rates #error


Howard Dutton
 
Edited

On Sun, Dec 27, 2020 at 11:24 PM, Pupper wrote:
So according to this isn't Vref = Imax?
Exactly.  And all other (non TMC) step stick drivers I know of don't factor in the RMS current (*0.71) with their Vref formulas, so I adopted the convention here that TMC drivers use Vref = Imax for consistency.


Pupper
 

For the TMC2100 here is the formula:

So according to this isn't Vref = Imax?


Khalid Baheyeldin
 

On Sun, Dec 27, 2020 at 07:50 PM, Pupper wrote:
would the vref voltages be the same? For example if I wanted the 0.95A peak then I'd set vref to 0.95V?
No!

The Vref has a formula that is specific to the stepper driver that you are using.
Google the Vref formula and use that to get 0.95A.


Pupper
 

Oh okay thanks so much.

So those currents are peak values, and would the vref voltages be the same? For example if I wanted the 0.95A peak then I'd set vref to 0.95V?


Khalid Baheyeldin
 

On Sat, Dec 19, 2020 at 03:36 AM, Pupper wrote:
So for a 1.68A rated motor try 1V (which corresponds to 0.7A or about 42% of the rated current I think)?

No. 0.7A is low for that motor.

The formula is like this:

Minimum value to start experimenting with:
1.68*1.41*0.4 = 0.95A

Maximum value to use:

1.68*1.41*0.7 = 1.66A


Start with the minimum, test out slewing and tracking, and if it works, leave it as is.
If it is not working well (stalling, ...etc), then increase by 0.1A and try again.
Repeat until you find the optimal value.


Pupper
 

Oh ok interesting

I thought stalling might be caused by not enough current guess I was wrong

So for a 1.68A rated motor try 1V (which corresponds to 0.7A or about 42% of the rated current I think)?


Howard Dutton
 
Edited

On Wed, Dec 16, 2020 at 04:34 PM, Pupper wrote:
Should I increase vref?
No, likely that is already too high and you haven't taken the steps to make a Vref of 1.4V work (so drivers are overheating and cutting out.)

For those motors/drivers try Vref = 1V.


Pupper
 

Thanks for the reply :)

I think the motors are rated 1.68A.

The vref voltage is around 1.4V i think so the motor current is 1A rms.

Should I increase vref?


Khalid Baheyeldin
 

On Wed, Dec 16, 2020 at 04:20 AM, Pupper wrote:
The motors don't spin at all when tracking either.
That is called stalling.

What are the motor current rating?
What current did you set the current for the motor (via Vref)?


Pupper
 

Hi everyone,

My setup is on a perfboard with a Teensy 3.2, TMC2100 stepper drivers and unbranded stepper motors. The stepper motors are being fed 12V and the Teensy is powered through a USB cable connected to my laptop running Sky Planetarium.
The motors spin just fine when slewing, however during low rates (maybe less than 50Hz?) the motors don't spin at all and instead just whine. The motors don't spin at all when tracking either.

Does anyone know what I'm doing wrong?

Thanks so much :)