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Stepper motor tuning help

Posted by devinrayolsen 
Stepper motor tuning help
August 06, 2018 03:30AM
::: SETUP :::
I’ve got 5 high torque Nema 17 stepper motors with 1.8 deg. step angle (200 steps/revolution).
Each phase draws 2A, allowing for a holding torque of 45Ncm(63.7oz.in).

I’m running ramps 1.4 board with 5 pcs A4988 StepStick Stepper Motor Driver Modules (w/ Heatsinks).

::: QUESTION :::
Im having a heck of a time trying to determine what the correct voltage should be for my drivers given my motor types.
I know how to test and tune the voltage, but everyone online has a different number and I’m really confused now.

I’m asking cause I’ve done nearly everything I can think of to stop my extruder from skipping steps.. no clogs, very random skipping, does so high off the bed (150mm).
So now I’m down to voltage tuning and need some assistance.

Anyone else pick up local radio stations when tuning your stepper drivers with a jewelers screw driver? I swear it’s been amplified since I built a double sided foil insolation heat chamber around my printer.. (thanks ABS)

Edited 3 time(s). Last edit at 08/06/2018 03:33AM by devinrayolsen.
Re: Stepper motor tuning help
August 06, 2018 05:04AM
there is a Wiki page that describes, how to identify the shunt-resistor value and calculate Vref.
2A steppers are a bit to much for the A4988 even when you reduce it to 80% of max. current.
Re: Stepper motor tuning help
August 06, 2018 11:36AM
I tune my steppers based on how hot they get after being in use for a couple hours, warm but not hot to the touch is ideal. There are other things that can cause an extruder to skip steps, too much tension on the idler, humidity soaked plastic, a rough cold end/throat sticking to the plastic, the list goes on.

If your stepper driver gets too hot before you can make your stepper warm this is a sign that it just cant deliver enough voltage, a heat sink and active cooling fan can increase the max output by a bit but there are higher amp drivers that can go in place of a cheap A4988. [www.pololu.com] thats a four layer pcb unlike the common 2 layer designs and can deliver up to 2A. And [www.pololu.com] this can deliver up to 2.2A, not all DRV8825 are created equal, the chineese design is slightly different and causes many steppers to be quite loud and is probably lacking in performance compared to a genuine pololu

Edited 1 time(s). Last edit at 08/06/2018 11:43AM by DaGameFace.
Re: Stepper motor tuning help
August 06, 2018 11:57PM
Thanks guys, I never thought to think of the actual drivers being under rated for my stepper motors... but now that makes sense and explains why my garage sounds like a barrage of 1980s toy laser guns while under print..

Reguarding my steppers temps; they never got warm. I remember holding on to them having a hard time if I felt warmth or I was just transferring body heat prior to my heat chamber install.
They now get warm now due to my heat chamber, but just residual heat and noting excessive.

Looking at better drivers this weekend.
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