Best way to cool CIM motors?

[Richard Wallace]

Originally Posted by Ether

@OP: If you're willing, please tell us about your gearing. How many motor turns does it take to raise the boxes 1 foot?

Ether's question is directly on-point.

As an example: my team is using one CIM motor to drive our elevator. The CIM drives an AndyMark RAW Box (am-2372) with reduction ratio 14.2:1, which drives a second reduction stage made from VexPro gears with ratio 84:30, which drives a 36 tooth 5mm pitch timing pulley, which drives the elevator belt.

So, our overall gearing is calculated as follows:

At the pulley: 36 teeth/rev x 5 mm/tooth = 180 mm/rev belt speed

So our elevator moves 180 / 25.4 / 12 = 0.59 ft per pulley revolution, so to takes 1/0.59 = 1.69 pulley revolutions to raise our elevator one foot.

Multiplying this by our gear ratios gives 1.69 x (84/30) x 14.2 = 67.3 motor revolutions to raise our elevator one foot. At full voltage the CIM motor turns at ~5200 rev/min = 87 rev/sec, so the CIM motor could raise our elevator 87/67 = 1.3 ft in one second, if there were no load on it.

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Using the same method to calculate for the system with a Toughbox and a 42 tooth pulley gives 18.5 motor revolutions to raise the elevator one foot, and a no-load speed of 87/18.5 = 4.7 feet per second. This speed is probably too high, considering gamepiece loads and likely sources of friction, so it is not surprising that the CIM motors are running hot.