This is an interesting one. If you are unsure, how can you tell if your stepper motors are 200 (1.8 degree) or 400 (0.9 degree) step motors?

Well the first port of call should be to have a look around on the body of the motor itself. Found a model number or some other identifying details? For example, found a sticker that says something like “Model: 42BYGHW811”? Well it should be pretty straight forward. Mash that number into Google, pull up the results and start looking through the tech specs for the step angle.

When Google fails

So what about if you have no luck? Maybe Google couldn’t find anything about your stepper motor, or perhaps your buddy gave you a shoe box of mystery stepper motors, that don’t have any identifying marks on them at all?

Grab the shaft of your motor and start to spin it, you will find that it snaps, or steps. Twirl the stepper till you find a place that you can reliably snap back and forth between two adjacent steps. The difference between the two snaps is the step size for your stepper. We can crudely measure this with:

  • Blu-tack
  • Pen
  • Piece of paper
  • Protractor
  • A paddle pop / popsicle stick, or if you are married to someone in the healthcare profession, a tongue depressor like what your doctor shoves in your mouth when you say “ahhh”.

Blu-tack the tongue depressor to the shaft of your stepper, and use it as a ruler to draw a line on the piece of paper like below. Be careful to make sure the pen is as vertical as possible.

A photo of a popsicle stick stuck to the shaft of a stepper motor and it is being used as a ruler.

Turn the shaft one snap over. Be careful to make sure that it is only one snap, it is easy to accidentally move the stepper to far or to bend the stick without stepping the motor. Use the tongue depressor again as a ruler and draw a second line. The arc between the two lines is your step size. Grab your protractor and measure!

A photo of the angle drawn on a piece of paper after the ruler has been used twice.

If the angle between the two lines comes out at 1.8 degrees, your stepper is a 1.8 or 200 step motor. If it comes out at 0.9 degrees, your stepper is a 0.9 or 400 step motor.

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