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Unread 07-05-2009, 07:24
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Al Skierkiewicz Al Skierkiewicz is offline
Broadcast Eng/Chief Robot Inspector
AKA: Big Al WFFA 2005
FRC #0111 (WildStang)
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Re: Sensorless back_emf speed controller

g,
I don't see why not. There are some variables that come into play though. The ripple frequency/PRR is affected by wear on the commutator and brush assembly. I would guess it would be significant until the brushes fully wear in. I have not counted up the commutator segments on any of the motors so I can't give you an idea of frequency vs. motor rpm. The sensor would have to track over a wide range of frequency and varying DC levels but it should be possible. The harder part is getting rid of the brush noise and inductive kicks. Since the frequency is pretty low, some adaptive DSP might make things very nice for this application.
I think for this discussion, we should likely rule out using the brake mode on the controllers. If this proves to be possible, then adaptive motor control would be better than simple brake mode. Although the current demands go up, motor position control would prove much better than a short across the motor.
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Al
WB9UVJ
www.wildstang.org
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Storming the Tower since 1996.