How to drive Nemma 17 very Slowly

I’m building a telescope mount to track the stars. I’m using an arduino nano, an a4988 driver, and a nemma 17 to run the contraption. I’m running the stepper at 5 volts. I need the motor to run at 1.8 rpms and don’t need much torque. Is this reasonable or too slow to run reliably? When I attempt to run it at that speed using the StepperDriver library it refuses to turn. The slowest it will go is 3 or 4 rpms but even then it doesn’t seem to like it. It makes the least amount of noise at around 150 rpms. I tried with various microsteps but that doesn’t seems to help. Should I use a geared stepper instead? They are more spendy.

Stepping motors go as slow as you wish: 1 step per hour is fine. However for fine angular steps, you need a gear or toothed belt drive (microsteps are for smooth running, not for accurate steps).

I'm running the stepper at 5 volts

8 V is the minimum for the A4988 driver. I'm surprised it works at all. NEVER use the Arduino 5V output to power motors or servos.

If your motor is not running with the rated torque, it is because

  1. the motor power supply is inadequate, and/or
  2. the motor driver is inadequate, and/or
  3. you have not set the current limit on the motor driver correctly.

For help, post links to the actual stepper motor and motor power supply, post a wiring diagram and describe how you set the current limit.

This is really helpful. I’ll try it with a 12v supply.

Not sure a stepper would ever be really smooth enough for a telescope drive, due to the large cogging
torques they develop (even with loads of microstepping). Microstepping is the best way to
reduce the vibration.

You can probably just schedule steps directly for low rates of turn in terms of microseconds per
step such as:

void loop()
{
  static unsigned long next_time = 0 ;

  if (micros() - next_time >= MICROSECONDS_PER_STEP)
  {
    next_time += MICROSECONDS_PER_STEP;
    digitalWrite (step_pin, HIGH) ;
    delayMicroseconds (10) ;   // for slow opto couplers
    digitalWrite (step_pin, LOW) ;
  }
}

BTW its NEMA17, not nemma 17. NEMA stands for something, you can look it up
and discover all about US electric motor standards!

MarkT:
BTW its NEMA17, not nemma 17. NEMA stands for something, you can look it up
and discover all about US electric motor standards!

Actually there are thousands of NEMA standards. A motor mounting is one of them. The opening in the dash of your automobile where the radio, etc. sets is also a NEMA standard.
Paul

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