FAQ: How do stepper drives and motors get smooth motion and consistent torque at low speed?

Smooth operation at low speeds with consistent torque is possible using stepper motors and drives. It is accomplished by ensuring the drive and motor work together, and often by using microstepping.

Microstepping is driving the stepper motor such that each pulse does not complete a full step. Rather, a partial step occurs. This allows the motor to operate far more smoothly at lower speeds. If microstepping were not done at low speeds, then there would be jerky motion because the motor could not go any slower than its smallest step size.

To accomplish microstepping correctly, the drive and motor must work together. This means the drive must output the correct pulses to the motor, and the motor must be capable of using them. This is usually done by sending current in sine waves to the motor. If done correctly, the two sine waves line up such that there are no detectable “steps,” just smooth, fluid motion. Not all drives can do this, however, so be sure to check the documentation provided.

Even if the driver can provide the proper kinds of signals, there are still fundamental limits on stepper motor construction as well. These include the ability of the coils in the stepper motor to respond to the pulsed signals in the correct manner and the motor’s detent and holding torques. These factors can introduce some ripple into the operation of a stepper motor. While most motors are capable of microstepping, keep in mind that variable-reluctance stepper motors are not able to operate with microstepping. This is a product of their construction and changing the drive cannot cause a variable-reluctance motor to operate with microstepping.

Microstepping can allow stepper motors to operate smoothly at low speeds. Manufacturers have various methods and algorithms available to them. As such make sure to consult the documentation and ask the manufacturer any questions to ensure that the selected drive and stepper motor are compatible and able to microstrep. For more information, read this article on microstepping, full stepping, and half stepping.