1. DC Motors, Stepper Motors, H-bridges DC Motors Stepper Motors Motor Control Circuits – Relays – H-bridges

2. AC versus DC Motors AC motors are not very flexible w/o a transmission – They can only turn in one direction – The speed is controlled by the design of the motor and the frequency of the AC current source (60Hz) DC Motors can be operated more flexibly – They can turn in either direction based on the polarity of the applied voltage – The speed is controlled by the magnitude of the voltage

3. DC Motors A DC motor has coils on a rotating electromagnetic armature in a fixed or variable magnetic field A commutator connects the DC power source in sequence to the coils in the armature as it turns Commutator end view: + - - + BrushesCommutator Electromagnetic Armature Coil (1 of Several) Fixed /Variable Field Magnet

4. DC Motors A continuous voltage across the brushes will keep the motor turning in either one direction or the other depending on the polarity – A higher voltage across the brushes will make the motor turn faster – A lower voltage across the brushes will make the motor turn slower The commutator sparks as it turns creating EMI or possible explosion hazard

5. Stepper Motors A stepper motor is a DC motor that has fixed magnets on the armature It does not use a commutator to automatically energize/de-energize different magnetic coils The ends of the coil windings in the field are alternately energized and de-energized by an external control circuit in a desired sequence The order and dwell time of the voltage to each coil controls the direction and the speed

6. Stepper Motors A stepper motor can be held in a fixed position by pausing the sequence and keeping one coil energized for the duration of the hold time Hence, a stepper motor can be used in similar applications as a servomotor (studied in CS341) – It can be moved to and held in a desired position – It can be rotated continuously at a controlled speed The control is all externally implemented

7. Types of Stepper Motors Many possible geometric arrangements of the: – Fixed magnets on the armature – Electromagnetic coils in the field around the armature References: http://homepage.cs.uiowa.edu/~jones/step/types.html Our Mercury Motor is a Bipolar Stepper Motor

8. Stepper Motors - Heat Stepper motors are designed to operate at a high temperature and can get hot (~ 80 deg C) If this causes a problem, try the following: – Lower the voltage (But I found the Mercury motor will not step/hold reliably at 9 VDC versus 12 VDC) – Turn off the power to the coils when not in use (Expect that the motor will slip out of position) – Mount the motor on a heat sink to dissipate heat – Use a fan to create air flow over motor / heat sink

9. Motor Control Circuits A motor control circuit: – Provides power to the motor coils in either polarity – Allows the external logic to control direction/speed There are two basic types of motor controllers – Electromechanical relay based controllers – Semiconductor based controllers (H-bridges) Each type has its advantages and disadvantages We’ll use our elevator motors as an example

10. Relay Motor Control Circuit Two relays can be used to provide on/off and up/down control for our elevator DC motor Ground + 9 VDC - + + - To Arduino Output Pins & Ground To Motor Power Supply Red Black Yellow Safety switch: Stops “up” when the car hits switch NO NC Up Down

11. Relay Motor Control Circuit Advantages – Uses simple, robust electromechanical devices – Can handle high voltages and large currents Disadvantages – Requires periodic maintenance (cleaning contacts) – Relatively slow due to inertia in mechanical parts – Contact make/break/bounce sparks creating EMI or possible explosion hazard Example: Used under the hood in cars

12. Relay Motor Control Circuit A DC motor such as the drive motor for our elevator system requires one circuit per motor – The direction is determined by one relay or the other being turned on - closing normal open (NO) contact A bipolar stepper motor such as the Mercury Motor requires two circuits per motor – Each coil is turned on and off in a selected direction in sequence to change the position continuously – One coil can be left on in a selected direction to hold in a desired position

13. Bipolar Motor - Relay Shield Wiring Arduino Uno Don’t Connect Positive Sides + 12 VDC NC NO Connect Grounds BlackBrownOrangeYellow Stepper Motor Coil A Stepper Motor Coil B Pin 7 D0 Pin 6 D1 Pin 5 D2 Pin 4 D3 Relay Coil 0 Relay Coil 1 Relay Coil 2 Relay Coil 3 Clockwise + - - + + - - + Counter CW

14. H-bridge Motor Control Circuit An electronic version of previous relay circuit Can be implemented with individual components http://www.youtube.com/watch?v=A_JNjAFo1f4 Can use an L298 H-bridge component – Two independent H-bridge circuits per component – Needs external “snubber” or “flyback” diodes

15. H-bridge Motor Control Circuit Half of an L298 H-bridge can be used to provide on/off and up/down control for a DC motor - + + - L298 H-bridge (Side A) +9 or 12 VDC Connect Grounds Snubber Diodes Snubber Diodes Arduino Uno Pin 2 Pin 3 Pin 7 Pin 6 Pin 5 Pin 9 Pin 4 Pin 8 +5 VDC Pin 1 Input 1 Input 2 Enable A Vss Vs Up DownRed YellowBlack Safety Switch

16. H-bridge Motor Control Circuit Advantages – No periodic maintenance is required (no contacts) – Fast switching speed available (limited by motor) – No EMI or possible explosion hazard due to sparks Disadvantages: – Limited voltage and current handling capacity – Vulnerable to EMI/EMP or damage due to electrical transients (may need metal shielded container and “snubber” or “flyback” diodes)

17. H-bridge Motor Control Circuit A DC motor such as our elevator system drive motor requires one H-bridge per motor – The direction is determined by the inputs (1 or 2) – The motor can be turned on and off by the Enable A A bipolar stepper motor such as the Mercury Motor requires two H-Bridge circuits per motor – The direction is determined by the ordering of the logic signals to the inputs (1, 2, 3, or 4) – The speed is controlled by the speed of sequencing

18. H-bridge Motor Control Circuit The Motor Shield provides uses both halves of an L298 component – one to control each coil of the stepper motor It is an electronic version of the Relay Shield diagram shown earlier It includes the “snubber” diodes on the board