DIfferent Year CIMS run at materially different speeds ?

[de_]

Our 4 CIM drive robot uses 2 from this year plus 2 from a few years ago all through new toughbox transmissions. At least one cim from a few years ago runs materially slower than this years. It has the same part number. Anyone else see different speeds ? Any chance they changed the KV rating between years but kept the same model number ?

[gorrilla]

most likely, the old cims are worn "in"

shouldent then, the old ones have slightly more power? my thinking is, as they "wear in" the brushes get roughed up and create more points for the electricity to pass through??

maybe I have this backwards?

[R.C.]

Are you sure it isn't the motors wearing in. Every motor runs faster and better when first used, but then it slows down overtime. Due to the fact that brushes get worn in; would be my thought.

Dang: GOT BEAT TO IT, MY THOUGHTS EXACTLY GORILLA

[Tristan Lall]

The specifications for the FR801-001 have changed over the years, but not by much. In 2003, the first year for that motor, the free speed was rated at 5 342 rev/min (±10%). In 2005, the free speed specification changed slightly to 5 310 rev/min (±10%). Power changed from 343 W to 337 W.

There's also the matter of whether the BI802-001A (CIM's number for the BaneBots M4-R0062-12) is actually equivalent to the FR801-001. I've never seen CIM's specification sheet for that motor to confirm this, but FIRST seems to feel that they are the same, and BaneBots publishes the same specifications as for the 2005-and-newer FR801-001.

And of course, the old AP801-001 (the Atwood Mobile MPD 71119 motor from 2002) has its own set of specifications. (Free speed either 5 500 rev/min or 5 600 rev/min, depending on which sheet you believe.) The old FR801-001 was based on this motor, without the inconvenient pinion shaft.

Was this the sort of variation that you encountered, or were you experiencing much larger discrepancies in performance?

*These changes were accompanied by a design change to the motor's keyway. Old CIMs had a keyway that continued off of the end of the shaft—probably cut with a Woodruff keyway cutter, while newer ones have a keyway with two rounded ends—probably milled with an end mill.

[Al Skierkiewicz]

Although used motors will have worn brushes, generally the brush will take on a wear pattern that gives it better contact with the commutator. If the motor was thermally stressed in the past, the lubricant may have become sticky and is producing significant drag on the shaft ends. If the motors were stored in contact with each other or have had some rough handling during it's life, then it is possible that the magnets have a reduced field. I have been forced to replace pancake DC motors that have lost magnetic strength from video tape recorders in the past.

[JesseK]

Interesting information. So it would seem that for years where drive train torque is critical, one would want to purchase 4 identical CIMs for the drive train to get maximum efficiency rather than use 2 from the KOP with 2 from an unknown year. Hmm.