DC Stepper Motor

• Typical Use: Position Control• Relative position (without feedback)• Easy to control:

# Steps moved = number of pulses inDesired Velocity Step Rate

• Inexpensive• Good holding torque • No brushes• Size Range:

1.3”L 10 oz-in $12.9”L 2000 oz-in $700.

• Can “lose” steps if load or pulse rate too high

Permanent Magnet DC Motor

• Typical Use: Variable Speed ControlPosition control is possible but requires additional

hardware

• Usually used with position or velocity feedback (optical encoder or tachometer)

• Control: Speed Input voltage (DC or PWM)

• Reduction gear heads common• Brushes wear out, spark, cause RFI• Size Range:

Micro 0.5” L x 0.2”D (pager vibrator) $5Big 13”L x 4”D 2 HP $1000

aTEaa

TLoad IKKV

R

KT

RPM

Torq

ue

V1

V2 >V1

Torq

ue

Stepper Motor Speed vs Torque

No lost steps w/acceleration

(slewing) control

No lost steps w/o acceleration

control

Lost steps (stall)

Step Rate

time

fmax

fmax

TLOAD

Step Rate - Hz ( Desired RPM)

Ref. (Figure 2.75), T. Kenjo, Stepping motors and their microprocessor controls, Oxford Press, 1984