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Thread: Servo motor H bridge control
picon face BY : Gerhard Fiedler email (remove spam text)


I'm working on a motor controller for a DC motor. I want to control the
position of a shaft connected to the motor through a gearbox. If I
understand that correctly, that's basically a standard servo configuration.
I plan on running the motor at around 10 to 20 A.

WRT the control of the H bridge through PWM, I see two possibilities. One
is to PWM between 0 and positive current (for forward movement) or between
0 and negative current (for backward movement). The other option would be
to PWM between positive and negative current, with 50% being "no movement".

I don't really know what the difference between the two forms is, in terms
of motor behavior or current draw. Are there any rules of thumb which
method to choose? (Since I'm working with relatively short, defined
movement profiles, I can switch the power off between movements, also in
the positive/negative PWM case, which doesn't normally "switch off".)

Also I don't know what to do with the freewheeling diodes around the
drivers. The MOSFET drivers are good enough (with their built-in zeners) to
run without freewheeling diodes. Is it a good idea to put them in anyway?
If so why? If it depends, on what? E.g. does the motor stop quicker without
freewheeling diodes?

<ycy2uy2s009u$.8quyc650rro5.dlg@40tude.net> 7bit

See also: www.piclist.com/techref/io/motors.htm?key=motor
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