Strange issue with LV8729

[dg00]

first some context

I am building a simple RA tracking motor for my telescope mount it needs to rotate at a versy presice speed to counter earth's rotation. First version I used

1. Arduino Nano
2. DRV 8825
3. NEMA 17 motor (17PM-K310-33vs from minebea) it has max current rating of 1.7 amp

all was okay but the motor vibration even at 1/32 microsteps was too bad most of my shots had wiggly stars due to vibration.
so I shifted to LV8729 thinking it will be smoother in operation. I connected the diver to nano as suggest by wiring diagram on fysetc website [see attachment]

I Have set vref to 0.6v for 1.2 amp current and reset and Sleep are set to high(3.3v) . the motor starts runs for half a sec then stops sometimes it vibrates and stops. Now the strange part if i touch the potentiometer on driver with some metal object the motor starts running again and it keeps running as long as i keep touching the potentiometer.

here is my code

#define DIR 2
#define STEP 3

#define M0 4
#define M1 5
#define M2 6
#define ENABLE 10


unsigned int dPause    =  5000;

void setup() 
{
  pinMode(DIR, OUTPUT);
  pinMode(STEP, OUTPUT);
  pinMode(M0, OUTPUT);
  pinMode(M1, OUTPUT);
  pinMode(M2, OUTPUT);
  digitalWrite(M0, HIGH );
  digitalWrite(M1, LOW  );
  digitalWrite(M2, LOW  );
  digitalWrite( DIR, LOW );
  digitalWrite( ENABLE, HIGH );
 
}

/* motor  FULL throttle */

void loop()
{
  
 
   digitalWrite(STEP, HIGH);
   delayMicroseconds(dPause);
   delayMicroseconds(dPause);
   digitalWrite(STEP, LOW);
   delayMicroseconds(dPause);
   delayMicroseconds(dPause);
  

}

Any suggestions will be much appreciated as I am at my wit's end trying to debug this issue.

[JCA34F]

Motor supply voltage (the voltage you have between VM and GND)? Torque required to move scope? If you touch the pot with a non metallic object like a match stick?

[MarkT]

Not sure a conventional "hybrid" stepper would ever be smooth enough for a telescope drive, due
to the large cogging torques they develop (even with loads of microstepping). The "hybrid" refers
to the use of magnetic reluctance in the rotor design - this is what allows 200 steps per revolution
rather than just 20 or so.

A low-cogging brushless or synchronous motor would be my choice for open-loop control. There will
be ways to mitigate vibrations with rubber isolating mounts and visco-elastic couplers too.

Changing from a DRV8825 to a LV8729 (both x32 microstepping) isn't going to do anything for
vibration, this is purely magnetic/mechanically limited when driven with the same microstepping.

[dg00]

JCA34F:
Motor supply voltage (the voltage you have between VM and GND)? Torque required to move scope? If you touch the pot with a non metallic object like a match stick?

motor supply voltage is 12v
if i touch the pot with non metallic stuff it doesn't work, the motor is not connected to telescope nw so only torque it needs should be equivalent to torque required to overcome moment of inertia of motor shaft. I popped the LV8729 and placed drv 8825 on same perfboard with same wiring same code it works so wirinf is also not the cause

[dg00]

MarkT:
Not sure a conventional "hybrid" stepper would ever be smooth enough for a telescope drive, due
to the large cogging torques they develop (even with loads of microstepping). The "hybrid" refers
to the use of magnetic reluctance in the rotor design - this is what allows 200 steps per revolution
rather than just 20 or so.

A low-cogging brushless or synchronous motor would be my choice for open-loop control. There will
be ways to mitigate vibrations with rubber isolating mounts and visco-elastic couplers too.

Changing from a DRV8825 to a LV8729 (both x32 microstepping) isn't going to do anything for
vibration, this is purely magnetic/mechanically limited when driven with the same microstepping.

i went for stepper because i want it to be a goto mount I tell it a star and positions itself to that star I am not sure i can achieve such accurate movement with a BLDC even with an encoder even few minutes off and you are not pointing correct star. also i saw significant improvement moving from 1/16 to 1/32 already so i thought 1/128 might do the trick

[JCA34F]

What will the motor RPM be while tracking? In "goto"?

[dg00]

JCA34F:
What will the motor RPM be while tracking? In "goto"?

[dg00]

Update I tried different stepper motors 28byj-48 to a beefy nema 23 (max coil current 1.5 amp)
both stuttered like other. I am thinking the issue might be Arduino nano ? i have not seen any builds with Arduino nano and lv8729, I have a spare blue pill and an Rpi lying somewhere maybe i will test with those tomorrow. if that fails then maybe i got a faulty driver

[hssyan]

hey, can you share a picture of the stepper and the datasheet if you have? i cant find the datasheet for the same motor you have so i dont know the specs of it as its not written anywhere on the label. sorry for my bad english.