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Unread 06-05-2009, 08:21
Unsung FIRST Hero
Al Skierkiewicz Al Skierkiewicz is offline
Broadcast Eng/Chief Robot Inspector
AKA: Big Al WFFA 2005
FRC #0111 (WildStang)
Team Role: Engineer
 
Join Date: Jun 2001
Rookie Year: 1996
Location: Wheeling, IL
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Re: Sensorless back_emf speed controller

Chris,
I am trying to remember the tests we did way back in January. It seems to me that we had a drive train with AM transmissions and two CIMs per. I only connected one motor on each side of the drive train so that I could intermittantly load the drive train by shorting out the other motor. As I remember, with no drive (stick at neutral) I would see about 6-7 volts as the motors coasted down from full throttle at the output of the JAG. Looking at the output of the driven motor open circuit I saw somewhat higher, maybe 8-9 volts. When we used the brake jumper, the output went down to less than a volt when the throttle was released. In all cases though, the brush noise was significant. It seems to me that worst case was winding down from full throttle to about 80%. Moving up to full throttle produced less noise and inductive kick. I also remember a distinctive ripple that was associated with the switching of the brush assembly. Don't quote me but I think the ripple voltage was in the 0.2-0.5 range. As the JAG is firmware controlled, I would think that a small code change might make EMF measurements much easier. Wink, Wink, nod, nod, to anyone from Luminary who is listening.
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Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
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Storming the Tower since 1996.