DC Motors, Stepper Motors, H-bridges

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

Fixed /Variable Field Magnet
-
Electromagnetic Armature Coil (1 of Several)
Brushes
Commutator
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.htm
  l
• 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
• Well 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

To Arduino Output Pins Ground
Up Down
NO
-
Red
9 VDC
To Motor Power Supply
NC
Ground
Black
NC
-
Black
Yellow
NO
Safety switch Stops up when the car hits
switch
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
Dont Connect Positive Sides
12 VDC
Stepper Motor Coil A
Stepper Motor Coil B
Arduino Uno
NO
NO
NO
NO
Black
Brown
Orange
Yellow
NC
NC
NC
NC
Connect Grounds
Relay Coil 0
Relay Coil 1
Relay Coil 2
Relay Coil 3

• Clockwise
• -
• -
• -
• Counter CW

Pin 7 D0
Pin 6 D1
Pin 5 D2
Pin 4 D3
14
H-bridge Motor Control Circuit

• An electronic version of previous relay circuit
• Can be implemented with individual components
• http//www.youtube.com/watch?vA_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

9 or 12 VDC
Vs
Snubber Diodes
Up Down
Red
Pin 4
5 VDC
Vss
Pin 2
Pin 9
-
L298 H-bridge (Side A)
Input 1
Safety Switch
Pin 5
Enable A
Pin 6
Input 2
Pin 7
-
Yellow
Black
Pin 3
Arduino Uno
Pin 8
Pin 1
Snubber Diodes
Black
Connect Grounds
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