Do CIM elevator motors overheat?

[mathking]

We tested the CIM coolers last year and found that while they had a small (but consistent and statistically significant) effect in keeping the motor from heating up too much (on the order of 5%), they aided quite a bit in cool down time. Particularly if a fan was included. I wish our design had been better and we had included them on the final drive train. I have a friend who design motors for a living who explained that while most of the heat is dissipated through the shaft for a motor like this, the case obviously heats up so it is dissipating non-trivial amounts heat through the case. And that if you are operating the motor in a way that causes it to heat up excessively, you should try to redesign. But if that isn't possible even small amounts of increases heat dissipation can have a positive impact on motor performance and longevity.

[FrankJ]

One concern I would have with a stalled motor is the effect on the commutator. With the shaft even rotating slowly you are spreading the current over all the segments rather than the 2 the brushes are on with a stalled motor. Other that that--what Adam said.

[Ether]

Originally Posted by Ether

Richard Wallace has conducted and reported some excellent tests documenting this. I'll post a link later unless someone else beats me to it.

Here's one report I found:

http://www.chiefdelphi.com/forums/sh...13#post1215913

[MrForbes]

Originally Posted by marccenter

When the CIM elevator motor stops moving to hold a tote at a given height it is effectively stalled (motor speed nearly zero) and maximum current is drawn.

This doesn't sound quite right. A motor's rated stall torque is not the same as the torque required to hold a specific load in one place. If you figure out the torque required to do that with your design, then you can figure out how much current the motor will require to maintain that torque.

It might make the motor smoke...it might not.

[Thad House]

Originally Posted by marccenter

Dear CD,

I was wondering if any teams that have progressed further into their build so far have determined that the elevator CIM motors overheat due to stalling?
I am assuming you are using a gearmotor attached to a CIM with a gear reduction ratio in the order of 50 to perhaps 90:1.

When the CIM elevator motor stops moving to hold a tote at a given height it is effectively stalled (motor speed nearly zero) and maximum current is drawn.

Have you found that your CIM elevator mount overheats in a two minute match? Were you holding one, two, three, or four totes?

Have you found it necessary to add an active braking mechanism to aid in the problem?

Why use such a big reduction? Unless you are using a pulley that is about a foot in diameter, that will most likely be too much reduction, and too slow.

If an average pulley/sprocket is about 2.5 inches in diameter, a 70:1 reduction off of a CIM will have a free speed of 0.87 ft/s, and a stall force of 1200 lbs. If you had to stall a CIM to hold up 60 lbs at that reduction, you would be using 5% of your stall torque. A CIM could do that basically forever without problems.

[Ether]

Originally Posted by marccenter

When the CIM elevator motor stops moving to hold a tote at a given height it is effectively stalled (motor speed nearly zero) and maximum current is drawn.

The current draw is only what is required to produce the torque necessary to hold the weight. This in turn depends on the gear ratio.

Here's an excellent video explaining motor selection and gearing.