Quote:
Originally Posted by Billfred
... If it has to run all day at a demo, that's yet another thing. (We learned this nearly the hard way; after the season we stripped two CIMs off of our 2011 robot and used it for driver practice. Let's say we didn't get all the runtime we wanted before the motors were too hot to touch.)
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Excellent point, Billfred. Al related a similar story in
another thread recently; I recall that in Wildstang's case, they knew they would damage CIMs by continuous driving practice, pausing just long enough to swap in fresh batteries -- and they did it anyway because the practice time was more valuable to them than the CIMs.
Note also that a hot CIM case indicates a VERY hot CIM armature (that rotating electrical coil on the inside). Rated service life for a CIM, per its
data sheet, is 1000 cycles of 6 minutes ON followed by 30 minutes OFF; the specified mechanical load during ON time is 4 lbf-in (64 oz-in) at 4320 RPM, with the motor drawing 27 Amperes from a 12 Volt supply.
In my lab we have set up a CIM with thermocouples on the case and on the brush holder (inside). We will run several cycles at the specified service life load point and record temperatures to make a plot vs. time. When I have that data I will post it. But even without temperature rise measurements, many of us who have run CIMs for driver training while draining several batteries can attest that they can get much hotter than we ever see during FRC match play.
__________________
Richard Wallace
Mentor since 2011 for FRC 3620 Average Joes (St. Joseph, Michigan)
Mentor 2002-10 for FRC 931 Perpetual Chaos (St. Louis, Missouri)
since 2003
I believe in intuition and inspiration. Imagination is more important than knowledge. For knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution. It is, strictly speaking, a real factor in scientific research.
(Cosmic Religion : With Other Opinions and Aphorisms (1931) by Albert Einstein, p. 97)