Quote:
Originally Posted by Al Skierkiewicz
Karthik,
Four Megohms between case and either terminal is perfectly acceptable. The failure in last year's motors were zero ohms in the same test. The amount you measured (if in fact in the megohm range) could be moisture in the air or your finger tips. I would expect that the fault condition would be in the zero to 1000 ohm range. The fault, as documented by others, in 2011 motors occurred when one or more windings became shorted to the armature. To fully test motors, it requires that the tester connect one probe to a terminal (it does not matter which) and the other probe to the case while turning the motor several revolutions. If the meter suddenly drops to near zero, then that winding is defective. A digital meter set to the continuity beep position will beep on a bad motor when the short is reached. No beep and the motor is likely good.
On occasion, shorts also occurred with excess solder migrating into areas of the motor that bypassed internal insulation. The measurement/test would give the same results. I believe that some motors would not show the defect until run for a while. I would suggest that teams run the motors prior to any testing.
In response to Banebots, I agree it is unfair at this point to chastise an entire product line for the fault of one product. They are trying to correct a problem encountered by their customers. Give them a chance. As others have found there are other motors in their line that teams are using with confidence.
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Al, this precise test was run, with the motor displaying failure characteristics. The 775's we received were definitely defective. Also, last year motors that initially tested as good, all failed after use in practice or competition.