Quote:
Originally Posted by MattC9
Hmmmm.... Just our luck I went and checked our 3, 2 of which were conductive. What exactly makes them "bad"? I have not heard why exactly this a problem.
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This is a mfr defect carryover from last year. Appears Banebots may be dumping known defective 775's on FIRST as I and others contacted Banebots
but they resisted acknowledging there was a problem.
I personally performed failure analysis, witnessed shorted turns to rotor core.
RS-775 rotors use epoxy coated core laminations as insulation, ineffectively.
(most motors use brown fiber insulation. check out CIM rotor. Epoxy, properly quality controlled, MAY allow a more compact motor & less labor to mfr)
Enamel windings short at iron lamination corners via break thru at tight bend.
Two windings shorted behaves as a shorted transformer winding
causing no load motor current to quickly increase, depriving motor of torque
if short to motor case = robot AL frame, it is Illegal and failed at inspection
(theoretical remedy: electrically isolate each motor to pass inspection, but problem will likely escalate as more turns shorted draws higher current & produces less torque; high localized heating leads to catastrophic smoke)
Shorts I measured were typically ~0.1 ohm to case (either terminal to case)
which requires a careful low ohm set-up
It's a smoking gun again this year.. This is a great well made motor otherwise.
PreTesting out of new box is essential if decision to use these.
At a regional last year 70% of new boxed spare parts 775's were shorted!
causing huge delays for teams counting on them (Team 207 et al)