Hobby Milling

Choosing the right driver for you stepper motor is important because it will allow you to get the maximum amount of performance out of your motor. There a few types of drivers available, each with their own characteristics.

Use a driver with a built-in chopper circuit

First and foremost, make sure that whatever driver you buy or build has a built-in chopper circuit. This is essential if you want to run your motors at a reasonable speed. A chopper effectively limits the amount of current flowing through your motor. This may sound like a bad thing, but in actuality, choppers are necessary for achieving high speeds. The reason is simple. If you have a driver which simply applies a constant voltage to your motor’s windings, you’d have to use a very low voltage to avoid overheating and destroying your stepper motor. Unfortunately, maximum stepper motor speed is highly dependent on voltage. A chopper circuit allows you to apply a high voltage to your motor in short bursts, which means your motor won’t be damaged, but will still run very fast. A popular chip combination is L297 and L298 from ST microelectronics.

Watch the amps

A critical thing to look for in a stepper motor driver is how many amps it is capable of sourcing. Some drivers list the maximum total number of amps while others list the maximum amperage per channel. So please be aware of that. Make sure that your stepper motor driver ratings meet or exceed the maximum amperage rating of your stepper motor so that you don’t leave any performance on the table. Finally, make sure that the driver allows you to adjust the number of amps it outputs so that you don’t damage your motor.

Bipolar or unipolar

As I’ve said in a previous article, if you’re making a CNC machine, you’ll almost certainly want to use a bipolar motor. You will need to make sure whatever driver you buy is designed to drive bipolar motors if that is indeed what you are using.

Microstepping

Normally, stepper motors have two modes, full step and half step. Most stepper motors for CNC machines have 200 full steps per revolution, or 400 half steps per revolution. But what if you want or need a higher resolution than that? Well, microstepping drivers may be for you! These circuits use a method to break each full step into fractional steps by using phasors. Basically, a microstepping driver may break down a full step into 64 very small steps. When using microstepping drivers, you should be aware that not all microsteps will be evenly spaced, so don’t depend on that too much. There is also approximately 30% less torque available to you. However, the major plus side is that microstepping can give you smooth motion at all speeds.

Where to buy stepper motor drivers

The easiest place to buy these things is eBay. Drivers are sufficiently simple such that hobbyists like myself have designed, built and even sold drivers. They’re cheap and easy to make.