Stepper motors are constant power motors. Unlike DC motors which rotate by create a reversing magnetic field stepper motors work by attracting a rotor core with magnetic coils aligned in a stator using discrete intervals called steps.
- Open loop, meaning there is no secondary sensor monitoring the position. In some cases this makes it cheaper to implement a digital controller.
- The errors associated with steppers are non cumulative so even running it in open loop will usually yield accurate positions.
- Full Torque Standing Still
- reliable, contactless
- low torque
- high vibration
- limited speed
- Resolution is limited to a multiple of it's step intervals.
- Continuous Power Device
Bipolar vs Unipolar
- Unipolar - motors are usually 5 or more conductors, all unipolars can be wired as bipolar
- Bipolar (series) - usually 4 conductors, require a h bridge driver
- Bipolar (Parallel)
- Bipolar (series)
- Constant Voltage (L/R)
- Constant Current (Chopper)
- Wave Stepping - (1 Phase on) This is the most power efficient method for stepper but supplies the least torque. this also makes it the least stable at higher speeds
- Full Stepping - (2 Phases on) offers half the resolution of wave stepping, but has a higher holding torque
- Half Stepping - (1 or 2 Phases on) a hybrid of wave and full stepping this offers higher resolution torque and speed.
- Micro Stepping - (continually varying currents)
- 4 wire - Bipolar
- 8 wire - Unipolar or Bipolar
Steps per revolution
Common Step angle 1.8 deg (200 steps per rev)
NEMA is a standard of stepper motor sizes. A 17 means the faceplate is 1.7inch wide. This also means that a motor that is a NEMA17 will fit onto the faceplate of any other NEMA17 motor. However the internals and the length of the stepper may vary and are usually defined by a longer more detailed suffix in the name.
NEMA 17 (<180 Oz. In torque)
NEMA 23 (180-400 Oz. In torque)
NEMA 35 (400-1200 Oz. In torque)
Japan Servo KH42HM2-951
Step Angle = 360/S (S = steps)