How to Choose a Stepper Motor?

Stepper motors come in all sizes and resolutions. Even though our conceptual schematic of a stepper motor performs a full rotation in four steps, most steppers motors have higher resolution. Some stepper motors rotate 7.5°per step, others rotate as little as 0.9°per step. Some stepper motors are strong enough to control X-Y tables, others only need to move the head of a CD-player.

In general, stepper motors of smaller sizes (1 inch diameter and about 0.75 inch thickness) have larger step sizes and less torque, while larger ones (1.5 inch cubed or so) have finer step sizes and more torque. While it is not an absolute guideline, motors that consume about 1W to 3W are ``about right'' in terms of torque and power.

The decision between a larger, fine step and high torque motor and a smaller, large step and low torque one is up to you. A smaller and lighter motor makes the overall size smaller and the overall mass lighter. However, due to the lack of torque and resolution, you need to gear down the drive axle of a smaller motor.

A larger, high resolution and high torque stepper motor can be directly attached to a drive wheel. This approach simplifies the mechanical design, but it adds more mass and increases the overall size. Most other school use these high torque and high resolution stepper motors.

The bottom line can be summarized as follows:

• Do you have enough linear resolution?
• Do you have enough torque for acceleration and deceleration?
• Is it realistic to carry enough batteries to last 15 minutes?