5. Ohm’s Law + - R E I E = I * R I = E / R R = E / I E = Voltage I = Current R = Resistance

6. Bar Magnet N S Lines of Flux Flux Density = # of Flux Lines / per unit area

7. Magnetic Poles S N Unlike Poles Attract Like Poles Repel N SS N

8. Current Carrying Conductor Lines of Flux Conductor Current Flow

9. Electromagnetic Coil Lines of Flux Flux Density Dependant on: Current # of Coils Core Material

10. Electro-magnetic Coils Direction of Current determines Magnetic Polarity

11. DC Motor Rotation Considerations Speed Torque

12. Speed Rpm - revolutions per minute Rotation of the shaft

13. Torque Torque is the product of Force x Lever Arm Length (Radius) Clockwise and Counter-Clockwise efforts are distinguished by differences in sign, + or -

14. DC Motor 1)Armature - coils of wire on the shaft 2)Field (Shunt Field) - coils of wire built into stationary frame A DC motor consists of two electromagnetic fields

15. Force Effect of Magnetic Fields Cancellation Reinforcement

16. Mechanical Effects of Magnetic Fields Rotation is a function of two fields pushing or pulling each other.

17. Principle of a DC Motor A DC motor has two independent electromagnetic fields –Controlled independent of each other Either field can influence the performance of the motor –Speed (rpm) –Torque (ft lb)

18. Motor Armature, Commutator and Field Wiring Arrangement F2 Brush F1 Brush Main Field Commutator Bars A1 A2 Armature Coils

19. Motor General Equation E T = K M  N + I A R A E T = Armature (Terminal) Voltage K M = Motor Constant  = Motor Field Flux Density N= Motor Speed I A = Armature Current R A = Armature Resistance

20. DC Motor Speed N = E T K M  K M  Motor Speed Varies by: E T = Armature (Terminal) Voltage K M = Motor Constant  = Motor Field Flux Density N= Motor Speed

21. DC Motor Torque T = K T  I A DC Motor Torque varies by: T= Motor Torque K T = Motor Constant (# poles, armature conductors)  = Motor Field Flux Density I A = Armature Current

22. DC Motor Horsepower Can be Determined By: HP = T x N 5252 HP= Motor Horsepower T= Motor Torque N= Speed

23. Speed Power Curve

25. Types of DC Motors Shunt Wound –Straight Shunt Compound Wound –Stabilized Shunt Permanent Magnet Series Wound Most DC Motors are: Note: Straight Shunt must be used with reversing/regen

26. DC Motor Review Speed is primarily determined by Armature Voltage Torque is determined by Armature Current

27. DC Motor Review Speed is primarily determined by Armature Voltage Torque is determined by Armature Current

61. Pulse Width Modulation (PWM) When we wish to control the speed of a motor we adjust its voltage. This being the age of digital electronics we have found a very fast and efficient way to vary a motor’s voltage. Using powerful transistors (MOSFETS), we switch the voltage supplied to the motor off and then back on very fast (sometimes millions of times a second). The amount of time the voltage is switched on compared to the amount of time it is switched off is also controlled. This is referred to as Pulse Width Modulation (PWM). The most important factor of the PWM signal is the duty cycle.

62. L293 H-bridge chip