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Unread 27-10-2003, 15:55
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kmcclary kmcclary is offline
Founder 830/1015;Mentor 66/470/1502
FRC #0470 (Alpha Omega Robotics)
Team Role: Engineer
 
Join Date: Aug 2001
Rookie Year: 1994
Location: Ann Arbor, MI
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Scopin' it out...

Quote:
Originally posted by Dave...
Keith,
We hooked up the 2004 Edubot controller up to an oscilliscope and found the following:

Frequency of signal: 58.8 Hz (17ms)
Amplitude: 5 V (positive going pulse)
PWM__Pulse width__"fwd/rev"__LED color
1_______.875ms________full rev____RED
127______1.5ms________neutral_____ORANGE
254_____2.07ms________full fwd____GREEN

I hope this helps.

Dave...
Definitely! Thanks! OOC, While you're set up - Does "0" also yield .875ms, or something lower?

Gee, are you up for an experiment??? If it's not too much trouble, would you like work together to plot either a chunk, or even the entire transfer function of an 884?

FYI, I wish to EVENTUALLY collect this table at high resolution:
edubot pwm in / data value / edubot pwm out / led color / 884 motor direction & pwm width across a resistor.

Given that and the motor spec sheets, I can then plot all of the transfer functions, motor power curves, etc., so we all know EXACTLY how they behave, how the deadband REALLY works, etc.. If you're game, I can set up an experiment for you and send you the procedure. You then send me the raw data back. I'll plot, analyze, and post the results for everyone.

If not, that's OK. Can you at least take about three equally spaced Value to PWM data points on each side of center, and find out where the 884 LED color change points REALLY are? I just want a clue as to the linearity, and where the 884's REALLY kick in "from neutral". I'll have the students do the rest later once we get a Win2K system at the school so we can try out the EduBot CPU.

FYI, we're just crippled right now or I'd do it myself. It's driving me nuts. We're finally moved into the school this year, but the entire school DISTRICT is one big *MAC* house. NO Windows boxes at ALL. We can't do a thing with programming yet at the school (or even fire up and download the EduBot defaut programs) until we run the politics AND finances to get at least ONE Windows system in and set up to run the MPLAB environment! We have C++ compilers, so we THOUGHT we'd be OK, but because of FIRST's system reqs, we now find we can't crunch and download into the Edubot. That shocked us. No one on our team even has a spare laptop or system capable of the environment to loan us either, so we're scrambling. (And no, I'm not trying to beg here for one.)

Let me know if you're game for this experiment.

Thanks, Dave! And BTW, I LOVE your tagline!

- Keith
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Keith McClary - Organizer/Mentor/Sponsor - Ann Arbor MI area FIRST teams
ACTI - Automation Computer Technologies, Inc. (Sponsoring FIRST teams since 2001!)
MI Robot Club (Trainer) / GO-Tech Maker's Club / RepRap-Michigan) / SEMI CNC Club
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