Motor driver

There are many kinds of motor drivers:

• servo motor controller
• stepper motor controller
• DC motor controller ("brushed")
• AC motor controller ("brushless")
• ... (todo: fill in the other kinds) ...

A DC motor controller that is 'reversible' generally uses an 'H bridge'. This 'H-bridge' uses four output drivers in a configuration that resembles an H where the load is the cross bar in the middle. The lines on either side of the load (the downward strokes in the H) represent a series connection of a pull-up driver and a pull-down driver. This allows each terminal of the load to be connected to either the positive supply rail, or the negative supply rail. This allows a positive, negative or zero voltage difference across the load. This load voltage is then utilized to provide the desired control required of the motor. The various combinations can give a 'forwards' torque on a DC motor, a 'backwards' torque on the same motor, can allow the motor to free-wheel (without any applied torque) or can provide a locking of the motor such that it resists any attempt to rotate it.

A single phase AC motor is generally driven in the same way as a DC motor, however instead of operating the motor drive as a constant DC voltage (in either the 'forward' or 'reverse' direction) the AC motor is driven by an approximation to a sinewave. This approximation is created using the H bridge and driving it with a PWM input such that both the positive and negative voltage periods are the same. This is normally achieved either using a sawtooth waveform compared against a sine wave reference, or is done using a lookup table in a microcontroller.

A similar method is used to drive multiphase (3-phase) AC motors, however instead of just using an H bridge, only a half H bridge is used per phase (3 half-bridges). Each phases half bridge is then driven in the same manner as for the single phase motor, with a phase difference between the phases as appropriate.

Most stepper motor controllers uses 2 independent H bridges (4 half-bridges) for the 2 independent coils of a stepper motor. Each possible state (one bridge driving current one way, the other way, or free-floating) of both bridges gives 4 "full steps", 4 "half-steps" between the full steps. The "microstepping" motor controllers use PWM to gradually change in a sine-wave-like manner from adjacent full-steps and half-steps.

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external links

A random collection of semi-related links (please prune out the irrelevant ones):

• H-Bridge by Bob Blick
• the Open Source Motor Controller Project
• LiniStepper $30 each; Open Source! Circuit Diagram, PCB (Board) Layout, and PIC Software all available. Nice photos of the LiniStepper at http://www.piclist.com/techref/io/stepper/linistep/lini_bld.htm .
• "Design of a High Current Bipolar Stepper Motor Driver"
• H-Bridge Fundamentals An in-depth article on the design of Mosfet H-Bridges
• PMinMO.com Open Source circuits and information on stepper motor controllers]
• ePanorama ePanorama Motor Control page
• "Electronic Design of DC Motor Drives" has detailed schematics and PCB layout for a system that has a PC send commands through the serial port to a Microchip PICmicro, which does PWM control of 2 H bridges. Each half-bridge uses a IRF9530N (100V 14A pfet plus flyback diode) and a IRF530 (IRF530NPBF: 100V 17A nfet plus flyback diode), driven by a small transistor inverter based on a BD135 npn, for a total of 12 discrete transistors.
• OpenServo wiki -- developing a digital servo motor that accepts "Go to position X" commands and also more complex curves, and returns actual servo position, speed, voltage and power consumption.
• MOSFETs and MOSFET drivers
• L297 stepper motor controller + L298 dual full-bridge driver: for driving one (4-wire) bipolar stepper motor (2 A); direction and step inputs; half-stepping; on-chip PWM chopper limits current. external diodes are required (preferably Shottky). (Both chips come in through-hole and SMT versions)
• L298 dual full-bridge driver can also be used to drive 2 independent DC motors (2 A each); external diodes are required (preferably Shottky). L293D is similar, but only rated up to 1 A, 36 V.
• SparkFun: EasyDriver v3 Stepper Motor Driver based on A3967 microstepping driver chip; up to 750mA, 30 V.
• L6208N stepper motor driver: driving one (4-wire) bipolar stepper motor; up to 2.8 A, 52 V. direction and step inputs. PWM current control; includes internal diodes. over-current and thermal protection. half-stepping. MC3479 stepper motor drive is similar, but only rated up to 350 mA, 16 V.
• Nanotec sells microstepping stepper motor driver chips (the IMT-901, IMT-902, and IMT-903) and assembled stepper motor driver modules.
• Reprap: Arduino has a long side-thread on various motor driver chips.
• lots of stepper motor driver chips
• Critical Velocity sells DC motor speed controllers and stepper motor controllers.
• Geckodrive sells DC motor speed controllers and stepper motor controllers.

astronomy telescopes use motor drivers:

• scope drive webring: a selection of Websites that display procedures to equip amateur telescopes with homemade computerized drive systems
• "scopedrive" for automating telescopes

Robots use motor drivers.

• Glendale robotics club (Glendale CA)
• "H bridges" by David Cook at the ROBOT ROOM(TM)
• "A Second Generation Speed Controller" by Chuck McManis. Can handle 200 amps continuously. Uses two PIC16F628 chips driving sixteen IRF1010E FETs: "(I like to call it a "two way SMP microkernel with serial cluster interconnect" as that sounds better than "a couple of PICs with their serial ports wired together" :-)"