1. Introduction to Brush DC Motor Control
The Brush DC Motor
August 12, 2013 Paul Nickelsberg Orchid Technologies Engineering and Consulting, Inc.

2. Electric Current – Magnetic Force
The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one meter apart in vacuum, would produce between these conductors a force equal to 2 x 10⁻⁷ newton per meter of length.
1 meter
1 A
1 meter
1 A
2 x 10⁻⁷ newton (kg m/s²)
0.556 x 10⁻⁷ ounce
In a vacuum

3. Electric Current – Magnetic Force
Current passing through wire in a magnetic field
Force is proportional to strength of current and strength of magnetic field

4. Electric Current – Magnetic Force
Stationary Part (Stator)
Rotating Part (Rotor)
We place a wire coil within a fixed magnetic field
As current flows in the wire, a varying torque is produced on the coil

5. Electric Current – Magnetic Force
We place a wire coil within a fixed magnetic field
As current flows in the wire, a varying torque is produced on the coil

6. Electric Current – Magnetic Force
Stationary Part (Stator)
Rotating Part (Rotor)
Paper-clip Brush DC Motor

7. DC Brush Motor Construction
Item
Description 1
Flange 2
Permanent Magnet 3
Housing 4
Shaft 5
Winding 6
Commutator Plate 7
Commutator 8
Graphite Brushes 9
Cover 10
Electrical Connection 11
Ball Bearings 1 2 3 4 11 5 6 8 11 10 8 7 9
Courtesy Maxon Corp

8. DC Brush Motor Construction
Magnets
Rotor
Stator
Brushes
Encoder
Assembly Bolts

9. DC Brush Motor Construction
Rotor
Laminated Core
Commutator
Cap and Barings
Windings

10. DC Brush Motor Construction
Incoming Wire
Brush Connection
Insulator
Brush Spring
Graphite Brush

11. DC Brush Motor Construction
Incoming Wire
Brush Connection
Insulator
Brush Spring
Graphite Brush

12. DC Brush Motor Construction

13. DC Brush Motor Construction

14. DC Brush Motor Selection

15. DC Brush Motor Selection
Speed
Max Speed Min Torque (No Load)
Min Speed Max Torque (Stall Load)
Speed-Torque Line
Proportional to Motor Voltage
Speed Decrease / Torque Increase
No load speed and stall speed change in proportion to input voltage
Speed-Torque Line
Torque

16. DC Brush Motor Selection
Speed
Weaker Motor
Stronger Motor
Speed-Torque Line
Greater Slope: Less Powerful Motor
Lesser Slope: More Powerful Motor
(Less Sensitive Speed is to Load)
Remember: These are constant voltage lines
Speed-Torque Lines
Torque

17. DC Brush Motor Selection
Speed
Weaker Motor
Stronger Motor
Speed-Torque Line
Greater Slope: Less Powerful Motor
Lesser Slope: More Powerful Motor
(Less Sensitive Speed is to Load)
Remember: These are constant voltage lines
Speed-Torque Lines
Torque
No Load Current
Current
Stall Current

18. DC Brush Motor Selection
Efficiency
Power
Peak Efficiency and Peak Power occur at different torque points
Torque

19. DC Brush Motor Selection
Torque Line
Efficiency Line

20. DC Brush Motor Selection
Torque Line
Efficiency Line

21. Introduction to Brush DC Motor Control
Join Us Tomorrow – Making Them Go
Application of Power to a Brush DC Motor
Field Effect Transistors
Field Effect Transistor Drive Circuits
High Side Drive
Low Side Drive
H-Bridge Motor Drive
PWM H-Bridge Drive Control