ELECTRIC MOTORSELECTRIC MOTORS

An Introduction to DC and An Introduction to DC and Stepper MotorsStepper Motors

Electric MotorsElectric Motors

• Electric motors are Electric motors are everywhere! everywhere!

• In your house, In your house, almost every almost every mechanical mechanical movement that you movement that you see around you is see around you is caused by an AC or caused by an AC or DC electric motor. DC electric motor.

Direct Current MotorsDirect 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 MotorsDirect Current Motors

Direct Current MotorsDirect Current Motors

Brushed DC MotorBrushed DC Motor

• The brushed DC The brushed DC motor is one of the motor is one of the earliest electric earliest electric motor designsmotor designs

• Easy to understand Easy to understand design design

• Easy to control Easy to control speed speed

DC STEPPER MOTORSDC 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 MOTORSDC STEPPER MOTORS

DC STEPPER MOTORSDC STEPPER MOTORS

• Voltage Rating Voltage Rating – provides desired torqueprovides desired torque

• Resistance-per-winding Resistance-per-winding determinesdetermines– the current draw of the motorthe current draw of the motor– Maximum operating speedMaximum operating speed

• Degrees per StepDegrees per Step– Sets the number of degrees the shaft Sets the number of degrees the shaft

will rotate for each full stepwill rotate for each full step

UNIPOLAR STEPPER UNIPOLAR STEPPER MOTORMOTOR

• Relatively easy to controlRelatively easy to control• simple 1-of-'n' counter circuit can generate simple 1-of-'n' counter circuit can generate

the proper stepping sequencethe proper stepping sequence• 1 transistor per winding1 transistor per winding

UNIPOLAR STEPPER UNIPOLAR STEPPER MOTORMOTOR

• two center-tapped coilstwo center-tapped coils• represents the connection of a 4 -phase represents the connection of a 4 -phase

unipolar stepper motorunipolar stepper motor

UNIPOLAR STEPPER UNIPOLAR STEPPER MOTORMOTOR

• 6 wires with a center tap on each of two coils6 wires with a center tap on each of two coils

IDENTIFYING WIRESIDENTIFYING WIRES

• Check make and model to see if Check make and model to see if wire colour code is availablewire colour code is available

• Observe the wires to see if you can Observe the wires to see if you can identify groups of 3 wiresidentify groups of 3 wires

• Measure resistance between wires Measure resistance between wires • Wire with lowest resistance is Wire with lowest resistance is

power wirepower wire

IDENTIFYING WIRESIDENTIFYING WIRES

• 6 wire motors6 wire motors– Groups of 3 wiresGroups of 3 wires– 1 power & 2 signal1 power & 2 signal

• 5 wire motors5 wire motors– 1 power & 4 signal wires1 power & 4 signal wires

• power wire has power wire has lowest lowest resistance to the resistance to the othersothers

CONTROL PROGRAMCONTROL PROGRAM• Once wires identified and connected to the Once wires identified and connected to the

circuit: a program is needed to run the motorcircuit: a program is needed to run the motor• Example Turing Program:Example Turing Program:

looploopparallelput (1)parallelput (1)delay (500)delay (500)parallelput (2)parallelput (2)delay (500)delay (500)parallelput (4)parallelput (4)delay (500)delay (500)parallelput (8)parallelput (8)delay (500)delay (500)

end loopend loop

STEPPER MOTOR STEPPER MOTOR CONTROLCONTROL

• 4 signal wires fired in the correct sequence will 4 signal wires fired in the correct sequence will turn the motorturn the motor