Published June 7, 2026
If you are new to motion control, you may have heard the terms "stepper motor" and "step motor controller" but are not sure what they mean or how they work together. This article explains step motor controllers in plain language, covering the essential concepts you need to understand.
A stepper motor (also called a step motor) is a brushless DC electric motor that divides a full rotation into a number of equal steps. A standard two-phase stepper motor has 200 steps per revolution, meaning each step is 1.8°. By energising the motor windings in a specific sequence, the motor's rotor moves from one step position to the next, locking into place magnetically at each step.
This makes stepper motors ideal for position control without needing an encoder or feedback system — at least in theory. In practice, open-loop operation can be unreliable under load, which is why closed-loop controllers were developed.
A step motor controller is the electronic circuit that drives a stepper motor. It performs two essential jobs:
The controller receives a "step" pulse on its input pin. For each pulse, it advances the motor by one microstep or full step, depending on the microstepping setting.
Microstepping divides each full step into smaller increments by partially energising two adjacent windings simultaneously. Common resolutions are 1/16, 1/32, and 1/256. Higher microstepping produces smoother motion and less vibration, especially at low speeds. The uStepper S32 supports up to 1/256 microstepping for near-silent operation.
Holding torque is the maximum torque the motor can exert when stationary with rated current applied. It is a key specification for applications that must hold position against a load, such as a CNC Z-axis or a robotic arm joint. A closed-loop step motor controller can maintain holding torque even when the motor is under stress, while an open-loop driver may lose steps and let the load slip.
The current limit is the maximum current the driver can supply to each motor winding. It must be set to match the motor's rated phase current. Setting it too high overheats the motor; setting it too low reduces torque. Many controllers, including the uStepper S32, allow current to be set via a simple trimpot or software.
Open-loop control works like pushing a button and assuming the door opens. The controller sends pulses and trusts the motor follows. If the motor encounters resistance and skips a step, the controller has no way to know.
Closed-loop control adds a sensor — an encoder mounted on the motor shaft — that measures the actual position. The controller compares the commanded position to the measured position hundreds of times per second. If there is a discrepancy, it adjusts the motor current to correct it immediately.
Think of it as the difference between blindfolded walking and walking with your eyes open. Closed-loop stepper motor control is always aware of where the motor actually is.
Most closed-loop controllers on the market are retrofit kits that require you to add an external encoder and mount it to the motor. uStepper takes a different approach: the magnetic encoder is integrated directly into the controller's PCB, and a small diametrically magnetised encoder magnet is attached to the motor shaft. This gives several advantages:
To learn more about how uStepper works, visit our What is uStepper? page.
When selecting a step motor controller, consider the motor's rated current, the required supply voltage, and whether you need closed-loop feedback. For hobby projects where cost is the main concern, a basic open-loop driver may suffice. For professional or production use — where reliability and accuracy are non-negotiable — a closed-loop controller like the uStepper S32 is the right choice.
Browse our product sheets to compare models and find the best fit for your project.
Browse our product sheets to find the right uStepper for your project, or visit the shop to order.