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Stepper Driver Adjustment

I used caution as stepper motors and drivers handle significant electrical power and can get hot, even burning hot (though they shouldn't be configured to allow that.) This is how I set them:

1. Assembled OnStep. Confirmed the wiring of the stepper drivers and bluetooth, etc. to the Arduino.
2. Configured and uploaded the firmware.
3. Plug/connected my stepper motors into the drivers. Never disconnect a stepper motor if the system is powered up.
4. Adjusted each driver's (BED, DRV8825, etc.) pot to it's minimum power position.
5. Connected OnStep USB to my computer and also the motor supply to the stepper drivers (I used a regulated 12VDC power supply, along with a switching ~12VDC to 24VDC step-up converter.)
6. Opened a serial console in the Arduino software then typed ":A1#" - this *starts the equatorial tracking pulses (RA).
7. Adjust the RA/Azm stepper motor current following one of the methods below (A or B.)
8. From the serial console in the Arduino software type ":R2#:Ms#" - this starts the Dec motor moving.
9. Adjust the Dec/Alt stepper motor current following one of the methods below (A or B.)
10. The stepper motors might very well run in the wrong direction (depending on wiring and stepper/gear-train design.) Each axis can be reversed in Config.h if needed. Doing short gotos from a Planetarium program lets you see on the computer screen which way the OTA should move and can help you figure out which axis needs to be reversed.

 

Adjusting current

Method A:  Tune using Vref: 

This video at the Pololu website is an excellent resource and should be watched by anyone unfamiliar with the procedure.  Refer to the Pololu RepRap A4988 and DRV8825 page for Vref setting information.  For the Silent Step Stick TMC2100 (and TMC2130?) The RepRap TMC2100 page provides similar information. For the LV8729, there are several versions, and the Vref depends on the resistors on the StepStick.

Method B

I used this with A4988 and DRV8825 stepper drivers but it's not very effective with Silent Step Stick drivers.  Slowly increasing the current with the potentiometer I could hear the pulse width modulation resonance (singing) and the motor started to move. Then, I adjust the motor so that the motion was smooth; too little and the motion was erratic, too much and it would cog to the full-step positions.  Be sure to monitor the stepper drivers and stepper motors for >half an hour (minimum) to be sure nothing overheats.

 


* =  If you have an Alt/Az mounted 'scope there is no tracking motion at startup since it's assumed you're pointed parallel with the Earth's axis of rotation (NCP or SCP.)  So the ":R2#:Mw#" command is necessary to start motion in Azm.