1. Announcements Bring two motors to lab this week.
Motors can be purchased at the Scientific Supply Store Sciences Center Laboratory (2nd Floor).
Prepare the leads as shown on the class website. Can do this in lab if desired.

2. Password Sync
…to login to Engineering labs, sync your password at
Still having trouble? Visit Engineering Network Services in 270 Ross Hall during normal business hours for assistance.

3. How a Motor Works
As current goes through armature it creates a magnetic field.
Opposites attract and likes repel causing rotational motion.

4. Motor Parts
The brushes make electrical contact to the moving armature. Wires would get twisted.

5. Motor Parts Continued
Current through the armature causes a magnetic field. The more current and more coils, the faster it turns.

6. Motor Parts Continued
PTC (Positive Temperature Coefficient) Resistor -
As temperature increases, so does the resistance- prevents burning up the motor.

7. Characteristics of Lego Motor
Constant voltage: Higher torque requires more current → lower speed. (Lego Car)
Constant torque:
Voltage, speed, and current increase together. (Lab)

8. Motors/Generators Motor Generator Appling a voltage, turns the motor
Turn the rotor (gas engine, water power, etc.) generate a voltage

9. Motor Equivalent Circuit
The faster the motor turns, the more the internal voltage cancels the driving voltage.
k is a constant that depends on the motor.
f is the rotational speed in revolutions/min (RPM).

10. Motor Control Signals Pulse Width Modulation (PWM)‏
Pulse Position Modulation (PPM)‏

11. Pulse Width Modulation (PWM)‏
Waveform in which the width of a pulse is varied
Can be used as a communication scheme
Can be used to vary the speed of a motor

12. Important Terms
Period (T) – the time to complete one cycle of the waveform (Units: seconds)‏
Frequency (f=1/T) – the number of cycles per second (Units: hertz, Hz=1 cycle/s)‏
Pulse width – amount of time the wave is high during one period
Duty Cycle – Pulse width / Period

13. Controlling Motors with PWM
Think of the pulses as someone pulsing the switch below
The longer they hold it, the larger the pulse width

14. PWM used to vary speed
As the duty cycle decreases, so does the average voltage delivered to the motors.
Hence your speed will decrease
Max speed = 100% duty cycle

15. PWM for SERVOS
Servos are motors that you can tell to turn to a position.
Based on the duty cycle you send them, they move to a corresponding position.

16. Pulse Position Modulation
Communication scheme in which the position of pulse varies in order to communicate a message.