Introduction to Brush DC Motor Control The Brush DC Motor August 12, 2013 Paul Nickelsberg Orchid Technologies Engineering and Consulting, Inc. www.orchid-tech.com

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

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

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

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

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

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

DC Brush Motor Construction Magnets Rotor Stator Brushes Encoder Assembly Bolts

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

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

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

DC Brush Motor Construction

DC Brush Motor Construction

DC Brush Motor Selection

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

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

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

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

DC Brush Motor Selection Torque Line Efficiency Line

DC Brush Motor Selection Torque Line Efficiency Line

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