Stepper Motor Torque
Estimate holding torque and power.
Understanding Stepper Motors
Stepper Motors divides a full rotation into a number of equal steps (usually 200 steps of 1.8°). Unlike DC motors, they have high holding torque at standstill and can move to precise positions without encoders.
They are the heart of the "Maker" revolution, powering essentially every desktop 3D printer (RepRap, Ender, Prusa) and hobby CNC machine.
Torque and Power Formulas
While exact torque curves require complex magnetic simulation, we can estimate key electrical parameters.
Power (W) = 2 × (Iphase × Vsupply)
Holding Torque ∝ N × I × Φ
Note: Stepper drivers (like A4988 or TMC2209) are "Choppers." They limit current. The calculated power is useful for sizing your power supply (e.g., specificing a 24V 10A supply for a printer with 5 motors).
Practical Applications
- 3D Printers: The NEMA 17 is the workhorse standard. High inductance motors work better for slow, high-torque Z-axis screws. Low inductance motors are better for fast X/Y movements.
- Camera Sliders: Used for smooth, repeatable timelapse motion control.
- Robotic Arms: Precise joint control without the jitter of servo motors.
FAQ
Why does my motor get hot?
It's normal. Stepper motors draw full current even when stopped to maintain holding torque. They are designed to run hot (often up to 80°C is safe, though too hot to touch).
What is Microstepping?
Instead of turning a full 1.8° step, the driver sends sine-wave currents to positon the rotor between the magnetic poles. 1/16th microstepping (standard) makes the motor quieter and smoother, but slightly reduces incremental torque.
Series vs Parallel Wiring?
For 8-wire motors: Parallel gives better high-speed torque but draws 2x current. Series gives better low-speed torque but drops off quickly at speed. Most NEMA 17s are fixed internal wiring (Bipolar).