Good motor practices

[pmangels17]

Make sure you don't run them above the recommended voltage. Also, don't overtighten the mounting screws, or if you have tapped screws in a gearbox, don't tighten them into the motor on the other side. Please don't drop them either, as that de-magnetizes the motor.

[nuttle]

Be very careful if you try to press something onto the shaft or to press the raised ring on the end of the CIM itself into anything. If you press the shaft of any motor, it is hard not to ruin the bearings. If the other end of the shaft is exposed, you can support it and even use it to help hold the shaft perpendicular to the press by using a piece of metal with a dimple drilled into it to keep the shaft from wandering. The raised ring on the end of the CIM is part of the endcap which can be fractured pretty easily in a press -- avoid any tight fits here.

[Wren Hensgen]

Have you ever actually broken one? I have been part of a few *ahem* questionable mounting practices, including using a hammer on the end of the CIM to get a gear onto the shaft.

[nuttle]

I've seen it done, both types of trouble. The minibot motors were fairly easy to mess up by pressing the unsupported shaft.

[mman1506]

Originally Posted by Wren Hensgen

Have you ever actually broken one? I have been part of a few *ahem* questionable mounting practices, including using a hammer on the end of the CIM to get a gear onto the shaft.

some past team member milled/hobbed a gear on the shaft of a CIM, I have no idea why but it still works.

[Mark Sheridan]

Originally Posted by mman1506

some past team member milled/hobbed a gear on the shaft of a CIM, I have no idea why but it still works.

Older CIM motors had a hobbed gear on their shaft. The last year I saw them was 2002. In 2003 they switched to key way. That might explain what you saw.

[Micah Chetrit]

Originally Posted by pmangels17

Please don't drop them either, as that de-magnetizes the motor.

Can you please explain how this works? I always tried not to drop motors for other reasons, but how does a drop affect magnetism?

[ttallo]

A magnetic is comprised of many small magnetic fields called domains basically electrons spinning in the same direction with their poles aligned. This creates a magnets pull. When you drop a magnet these domains slowly become misaligned with each drop and eventually you no longer have a magnet.

[Tungrus]

Before the magnet losses its magnetic "power", the motor will have mechanical damage like shaft gets bent or the casing cracks. With a bent shaft, the motor power is wasted, the bearing wears out and possibly seize and may result in motor stall and finally burn out. A cracked casing can be like a ticking bomb, you will never know when the guts or the whole motor falls out!

[FrankJ]

The magnets themselves are brittle. Very tight clearance between the magnet and the rotor. Magnet flakes from being dropped will lock up the rotor.

You don't see/smell the magic smoke from the cims because they are sealed. Al has posted pictures on another thread of what a smoked cim looks like.

[Richard Wallace]

A few links worth looking at:

Here's a link to some details of how CIM motor's heat up when loaded to their maximum mechanical power.

Here's a link to some measurements my lab made of CIM motor starting current. Special thanks to Russ Ether for his help with that testing. Here's another link to his white paper on how several FRC legal speed controllers limit the CIM motor's starting current.

Here's the link to Al Skierkiewicz's thread (mentioned above) on failure of a CIM motor due to extended, hard practice driving. Don't try this at home, or if you do then plan to replace the motors before your next competition.