Pololu A4983 + 3.9V, 600mA Stepper = Low torque?

Hello all!

My goal is to implement a stepper motor drive system for my home made telescope mount. I ordered Pololu A4983 stepper motor driver with voltage regulator and Pololu 3.9V, 600mA stepper motor for the purpose. Links to the products:

Driver: https://www.pololu.com/catalog/product/1202
Stepper: https://www.pololu.com/catalog/product/1204

I have done read the instructions and data sheets for the driver and stepper and I’m quite sure I have connected everything correctly. Motor turns smoothly and with constant velocity. I use Arduino Duemilanove to control the driver board.

The only problem is that the torque the motor provides in 1/16 step mode is extremely low. In full step mode the torque is only slightly better. I can easily stop the turning of the motor shaft by simply touching it lightly. I know that the torque goes down with micro stepping, but I was surprised that the torque is practically almost zero.

Do you have an idea what I’ve done wrong? I have set the current limiting to 600 mA by measuring the voltage on VREF pin. According to A4983 data sheet the current limit is calculated by I = U / (8*R), where U is the measured voltage from VREF pin and R is the resistance of current sense resistors (0.05 Ohms according to Pololu website). Hence, I set the voltage to 240 mV. I use 12 1A power supply for the driver board. The motor is heating up quite a bit, but I can still quite comfortably touch it.

Best regards,


How fast are you stepping, and what kind of torque do you get if you slow the speed way down or stop entirely?