Motor Tutorial Kevin M. Lynch  Laboratory for Intelligent Mechanical Systems Northwestern University Evanston, IL  USA
Types of Motors <ul><li>•  DC (brushed) </li></ul><ul><li>•  Stepper </li></ul><ul><li>•  RC Servo </li></ul><ul><li>•  So...
Types of Motors <ul><li>•  DC (brushed) </li></ul><ul><li>•  Stepper </li></ul><ul><li>•  RC Servo </li></ul><ul><li>•  So...
Types of Motors <ul><li>•  DC (brushed) </li></ul><ul><li>•  Stepper </li></ul><ul><li>•  RC Servo </li></ul><ul><li>•  So...
Types of Motors <ul><li>•  DC (brushed) </li></ul><ul><li>•  Stepper </li></ul><ul><li>•  RC Servo </li></ul><ul><li>•  So...
Types of Motors <ul><li>•  DC (brushed) </li></ul><ul><li>•  Stepper </li></ul><ul><li>•  RC Servo </li></ul><ul><li>•  So...
DC Motors <ul><li>Lorentz Force Law: </li></ul><ul><li>F = I x B </li></ul><ul><li>F  = force on wire </li></ul><ul><li>I ...
Inside a DC Motor
DC Motors <ul><li>V = IR + L (dI/dt) + k e  </li></ul><ul><li>   = k t  I  </li></ul><ul><li>V voltage </li></ul><ul><li...
DC Motor Specs
Driving a DC Motor <ul><li>Switches and relays </li></ul><ul><li>Transistors </li></ul><ul><li>Linear push-pull stage with...
H-bridge and PWM <ul><li>PWM:  Rapidly switch between S1-S4 closed and S2-S3 closed </li></ul><ul><li>Averages to effectiv...
L293 H-bridge chip
Practical Issues <ul><li>flyback diodes for “inductive kick” </li></ul><ul><li>heat sinks for transistors </li></ul><ul><l...
Gears <ul><li>Gear ratio G </li></ul><ul><li>   out =   in  / G </li></ul><ul><li>   out   =    G   in  (   = effici...
Encoder Feedback Another option: potentiometer US Digital
Feedback Control <ul><li>Proportional (Integral-Derivative) Control </li></ul><ul><ul><ul><li>Multiply position/velocity e...
Stepper Motor <ul><li>Bipolar:  4 wires </li></ul><ul><li>Unipolar:  5 or 6 wires </li></ul>+V alternately ground one end ...
Animation of Unipolar Taken fro m http://www.cs.uiowa.edu/~jones/step/
Driving a Stepper Use logic on/off signals at 2, 7, 10, 15.
RC Servo Motor <ul><li>3 wires:  power, ground, control </li></ul><ul><li>Control signal sets the position. </li></ul><ul>...
Solenoid <ul><li>Plunger attracted or repelled by current through a coil. </li></ul><ul><li>May be driven by a relay or tr...
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D cmotortutorial

  1. 1. Motor Tutorial Kevin M. Lynch Laboratory for Intelligent Mechanical Systems Northwestern University Evanston, IL USA
  2. 2. Types of Motors <ul><li>• DC (brushed) </li></ul><ul><li>• Stepper </li></ul><ul><li>• RC Servo </li></ul><ul><li>• Solenoid </li></ul>
  3. 3. Types of Motors <ul><li>• DC (brushed) </li></ul><ul><li>• Stepper </li></ul><ul><li>• RC Servo </li></ul><ul><li>• Solenoid </li></ul>Workhorse, high power Simple to use, two wires Torque proportional to current, steady state constant-load speed proportional to voltage Requires gearing Requires feedback
  4. 4. Types of Motors <ul><li>• DC (brushed) </li></ul><ul><li>• Stepper </li></ul><ul><li>• RC Servo </li></ul><ul><li>• Solenoid </li></ul>Useful for low-torque applications with no surprises No feedback required One step per pulse More involved driving circuit
  5. 5. Types of Motors <ul><li>• DC (brushed) </li></ul><ul><li>• Stepper </li></ul><ul><li>• RC Servo </li></ul><ul><li>• Solenoid </li></ul>High torque, useful for positioning applications Feedback and gearing built in Position commanded by persistent pulse train Limited motion (less than 1 revolution)
  6. 6. Types of Motors <ul><li>• DC (brushed) </li></ul><ul><li>• Stepper </li></ul><ul><li>• RC Servo </li></ul><ul><li>• Solenoid </li></ul>For on-off applications Simple to use Short stroke Powered in only one direction; requires external spring for return
  7. 7. DC Motors <ul><li>Lorentz Force Law: </li></ul><ul><li>F = I x B </li></ul><ul><li>F = force on wire </li></ul><ul><li>I = current </li></ul><ul><li>B = magnetic field </li></ul><ul><li>Right hand rule: </li></ul><ul><li>index finger along I, </li></ul><ul><li>middle finger along B, </li></ul><ul><li>thumb along F </li></ul>N S
  8. 8. Inside a DC Motor
  9. 9. DC Motors <ul><li>V = IR + L (dI/dt) + k e  </li></ul><ul><li> = k t I </li></ul><ul><li>V voltage </li></ul><ul><li>I current </li></ul><ul><li>R resistance </li></ul><ul><li>L inductance </li></ul><ul><li> speed </li></ul><ul><li> torque </li></ul><ul><li>k e electrical constant </li></ul><ul><li>k t torque constant </li></ul>  speed-torque curves for two voltages 2 - permanent magnet 3 - housing (magnetic return) 4 - shaft 5 - winding
  10. 10. DC Motor Specs
  11. 11. Driving a DC Motor <ul><li>Switches and relays </li></ul><ul><li>Transistors </li></ul><ul><li>Linear push-pull stage with op amp </li></ul><ul><li>Ideally: H-bridge and PWM </li></ul>
  12. 12. H-bridge and PWM <ul><li>PWM: Rapidly switch between S1-S4 closed and S2-S3 closed </li></ul><ul><li>Averages to effective voltage across motor between -V and +V depending on time spent in S1-S4 and S2-S3 states </li></ul><ul><li>Switch control signals are simply digital signals </li></ul><ul><li>Use an H-bridge chip or build out of transistors </li></ul>
  13. 13. L293 H-bridge chip
  14. 14. Practical Issues <ul><li>flyback diodes for “inductive kick” </li></ul><ul><li>heat sinks for transistors </li></ul><ul><li>capacitors to smooth voltage spikes </li></ul><ul><li>other noise issues, isolation </li></ul>
  15. 15. Gears <ul><li>Gear ratio G </li></ul><ul><li>  out =  in / G </li></ul><ul><li>  out =  G  in (  = efficiency) </li></ul><ul><li>Many types </li></ul><ul><li>spur, planetary, worm, lead/ball screw, bevel, harmonic... </li></ul>
  16. 16. Encoder Feedback Another option: potentiometer US Digital
  17. 17. Feedback Control <ul><li>Proportional (Integral-Derivative) Control </li></ul><ul><ul><ul><li>Multiply position/velocity error by a gain to get control signal (and perhaps add integral and derivative of that error multiplied by other gains) </li></ul></ul></ul><ul><li>Usually implemented on computer </li></ul><ul><li>Can be implemented with op amps </li></ul>
  18. 18. Stepper Motor <ul><li>Bipolar: 4 wires </li></ul><ul><li>Unipolar: 5 or 6 wires </li></ul>+V alternately ground one end of coil or other 1 4 2 3 A B A B R R R R L L L L L L R R R L
  19. 19. Animation of Unipolar Taken fro m http://www.cs.uiowa.edu/~jones/step/
  20. 20. Driving a Stepper Use logic on/off signals at 2, 7, 10, 15.
  21. 21. RC Servo Motor <ul><li>3 wires: power, ground, control </li></ul><ul><li>Control signal sets the position. </li></ul><ul><li>High pulse every ~20 ms determines set angle; pulse width between ~0.5 ms and ~2 ms, indicating the two ends of angle range </li></ul><ul><li>Internal gearing, potentiometer, and feedback control. </li></ul>
  22. 22. Solenoid <ul><li>Plunger attracted or repelled by current through a coil. </li></ul><ul><li>May be driven by a relay or transistor. </li></ul>

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