ELECTRIC MOTORS
An Introduction to DC and
Stepper Motors
Electric Motors
• Electric motors are
everywhere!
• In your house,
almost every
mechanical
movement that you
see around you is
caused by an AC or
DC electric motor.
Direct Current Motors
• overall plan
of a simple 2-
pole DC
electric motor
• A simple
motor has 6
parts, as
shown in the
diagram
Direct Current Motors
Direct Current Motors
Brushed DC Motor
• The brushed DC
motor is one of
the earliest
electric motor
designs
• Easy to
understand
design
• Easy to control
speed
DC STEPPER MOTORS
• Stepping motors are
electric motors without
commutators
• Commutation is handled
externally by the motor
controller
• Controller charges
opposite coils attracting
the center rotor magnets
DC STEPPER MOTORS
DC STEPPER MOTORS
• Voltage Rating
– provides desired torque
• Resistance-per-winding
determines
– the current draw of the motor
– Maximum operating speed
• Degrees per Step
– Sets the number of degrees the
shaft will rotate for each full step
UNIPOLAR STEPPER
MOTOR
• Relatively easy to control
• simple 1-of-'n' counter circuit can
generate the proper stepping sequence
• 1 transistor per winding
UNIPOLAR STEPPER
MOTOR
• two center-tapped coils
• represents the connection of a 4 -
phase unipolar stepper motor
UNIPOLAR STEPPER
MOTOR
• 6 wires with a center tap on each of two
coils
IDENTIFYING WIRES
• Check make and model to see if
wire colour code is available
• Observe the wires to see if you
can identify groups of 3 wires
• Measure resistance between
wires
• Wire with lowest resistance is
power wire
IDENTIFYING WIRES
• 6 wire motors
– Groups of 3 wires
– 1 power & 2 signal
• 5 wire motors
– 1 power & 4 signal
wires
• power wire has
lowest
resistance to
the others
CONTROL PROGRAM
• Once wires identified and connected to the
circuit: a program is needed to run the
motor
• Example Turing Program:
loop
parallelput (1)
delay (500)
parallelput (2)
delay (500)
parallelput (4)
delay (500)
parallelput (8)
delay (500)
end loop
STEPPER MOTOR
CONTROL
• 4 signal wires fired in the correct
sequence will turn the motor