Stepper Motor Drivers

Stepper motor drivers are the devices which convert the signals coming from the computer, and the power coming from the power supply into high power electrical signals that will power and move the stepper motors.

Stepper drivers come in many different forms, with many different ratings. There are small cheap drivers made for controlling tiny NEMA 17 size stepper motors, and big expensive drivers made for running big, powerful NEMA 34 size stepper motors.

The key with selecting drivers, is choosing one with good features and just a little more power than it needs to run your stepper motor.

For example the stepper motors I use on my own CNC router require 2.8 amps current, and around 50 volts. So I chose a stepper motor driver that was rated for up to 3.5 amps and 50 volts.

This is a very good match, my steppers will get all the power they need to run at their full potential with some left over. It’s always nice to have some head room, this will allow drivers to run cooler and extend their life.


Some features to look out for when selecting a stepper motor driver:

Micro-Stepping

The drivers ability to do micro-stepping will allow you to get more resolution and low speed performance out of your stepper motor. Many drivers will have the option of just selecting a micro-stepping mode such as 1/2 stepping, 1/4 stepping, 1/8, 1/16. You get the picture.

However inherent in how stepper motors work, they suit micro-stepping at lower speeds but suit full stepping at higher speeds. By full stepping at higher speeds, greater torque can be achieved.

A solution to this is morphing of steps; changing the micro-stepping based on the current speed of the motor. This feature is found in the Gecko brand of stepper motor drivers.

I highly recommend this feature but drivers without it still operate well, they just loose that additional edge of getting full performance out of a stepper motor. To find out more on micro-stepping go to my article: Stepper Motors vs. Servo Motors and read the section titled “Stepper Motors“.


Resonance Damping

Stepper motors have an inherent issue referred to as mid-band resonance. This instability can cause the stepper motor to stall when it reaches this mid-band. Obviously this is not good news for a CNC machine, for which we require constant and expected performance.

Fortunately many stepper drivers have a feature to negate the effects of mid-band resonance. This feature is often called something along the lines of resonance damping or anti-resonance. I really stress the importance of having this feature on your stepper motor driver. Be sure to look out for it!


Iso-optolated Step/Dir Pins

Iso-optolation separates an electrical signal and replaces it with light. This feature will keep your breakout board safe from the stepper driver, and the same is true in the reverse. This is a common feature on drivers, but is important to look out for. Safety is very important when it comes to these high powered devices. To find out more on opto-isolation go to my article: Breakout Boards and read the section titled “Opto-Isolation“.


Links to stepper drivers: