1 eric taseski, yihe huang, ronak mehta h-bridges and stepper motors 2
TRANSCRIPT
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Eric Taseski, Yihe Huang, Ronak Mehta
H-Bridges and Stepper Motors
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Standard DC Motors
Speed determined by voltage level.
Motor
Vcc
GND
+ -- +
4
Stopping
No movement, holds position.
Motor
Vcc
GND
STOP
5
Free Spinning
Disconnected, does whatever it wants.
Motor
Vcc
GND
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What if you want precision?
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Stepper Motors!
Precision movement via stepping
Can count revolutions
Can rotate continuously unlike a standard servo
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How Stepper Motors Work
Divides a full rotation into a number of steps.Move one ‘step’ at a time.
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Stepper Motors
1. The horizontal pair is driven with power in one direction. This pulls the oppositely polarized teeth to align with them.
2. The horizontal pair is de-energized, and the vertical pair is energized.
3. The vertical pair is de-energized, and the horizontal pair is energized in the opposite direction.
4. The horizontal pair is de-energized, and the vertical pair is energized in the opposite direction.
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How Stepper Motors Work
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Stepper Modes: Wave Mode
http://en.wikipedia.org/wiki/File:Drive.png
A
B
C
D
(codeproject.com)
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Stepper Modes: Full Step Mode
http://en.wikipedia.org/wiki/File:Drive.png
A
B
C
D
(codeproject.com)
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Stepper Modes: Half Step Mode
http://en.wikipedia.org/wiki/File:Drive.png
A
B
C
D
(codeproject.com)
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Stepper Motors Contd.
http://www.pololu.com/catalog/product/1205/specs
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How do we power them?
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H-Bridges!
Allows low voltage logic while driving external power to motors.
Easily control current in both directions, allowing motors to move forwards and backwards.
Useful for DC motors, stepper motors, servos, solenoids, etc.
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H-Bridges
Each half bridge is a transistor with an enable.
• LOW Voltage Input Control Logic• HIGH Voltage Output
Motor Voltage
Logic Enable
Motor
Logic Input
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H-Bridges
EN 1,2
EN 3,4
Input 1
Input 2
Input 3
Input 4
Output 1
Output 2
Output 3
Output 4
Vcc, Motor Supply Voltage
GND
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H-Bridge Pinout
-EN pins enable output (1 EN pin per pair)-A’s are control inputs-Y’s are outputs-Vcc1 is circuit logic voltage-Vcc2 is the motor supply-Grounds go to ground
http://www.ti.com/lit/ds/symlink/l293d.pdf
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Full-Bridge with DC Motor
Motor+ -Enable
Input A
Input B
ENABLE Input A Input B Result
1 1 0 Motor turns CW
1 0 1 Motor turns CCW
1 0 or 1 0 or 1 Fast Stop
0 0 or 1 0 or 1 Free Spin
1
0
1
0
1
1
- +
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How to wire up a stepper motor and the L293D
Left side can be adapted to our SmartFusion kits.
(codeproject.com)
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Protips #1-4
1. Heatsinks, or drive low to all pins to not drive current
2. Non-negligible voltage drop across H-Bridge
3. Varying PWM Duty Cycles can be used on ENABLE to control voltage supplied (speed control)
4. Frequency response of motor• Low PWM frequencies may create audible buzz or hum
• High PWM frequencies waste power
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ReferencesL293D explanation with Stepper Motor details: http://www.codeproject.com/Articles/151763/Motor-Primer-and-the-L293D-Quad-Half-H-Driver
Stepper motor configurations with microcontroller pins:http://www.8051projects.net/stepper-motor-interfacing/stepper-motor-connections.php
Microstepping (not covered):http://homepage.cs.uiowa.edu/~jones/step/micro.html
Different types of stepper motors explained:http://www.wimb.net/index.php?s=motion&page=52
Stepper wikipedia page:http://en.wikipedia.org/wiki/Stepper_motor
H-Bridge wikipedia page:http://en.wikipedia.org/wiki/H_bridge
Adafruit stepper with arduino tutorial:http://learn.adafruit.com/adafruit-arduino-lesson-16-stepper-motors/breadboard-layout
L293D Datasheet:http://www.ti.com/lit/ds/symlink/l293d.pdf
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Backup Slides
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H-Bridge with DC Motor
S1 S2 S3 S4 Result
1 0 0 1 Move CW
0 1 1 0 Move CCW
0 0 0 0 Free Spin
0 1 0 1 Brake
1 0 1 0 Brake
1 1 0 0 Shoot-through
0 0 1 1 Shoot-through
1 1 1 1 Shoot-throughhttp://en.wikipedia.org/wiki/H_bridge
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Microstepping
Half stepping with sinusoidal transitions between steps allowing theoretically infinitesimally small step sizes.
http://en.wikipedia.org/wiki/Stepper_motor