CIM Motors reusable?

[Richard Wallace]

Originally Posted by bobby5150

CIM motors are the most durable motors allowed in FRC.
...

I will second that. CIMs are some to the most durable motors I have worked with in any application. However, like any motor, they can be damaged by overheating. See this thread for a good example.

Also see this other thread for some details on how CIM motors heat up when loaded to their maximum mechanical output power.

As many long time FRC participants can attest, CIM motors typically last several seasons unless severely abused. Measuring their free current is an easy way to detect such abuse. Typically that will be about 3 Ampere when first started and will reduce to about 2.5 Ampere after running for a few minutes -- friction reduces a bit when the bearings warm up.

[Whippet]

I'd say go for it. The only CIM I've seen die was stalled while hooked directly to a battery with a prototype that needed more torque than the ungeared CIM was willing to provide. Needless to say, there was quite a bit of magic smoke that day.

[jspatz1]

Unless you have some reason to believe they have been damaged by severe over-heating, there is no reason not to use them again. Their useful life is far greater than the mileage seen in most FRC seasons.

[MikeE]

Originally Posted by Richard Wallace

I will second that. CIMs are some to the most durable motors I have worked with in any application. However, like any motor, they can be damaged by overheating. See this thread for a good example.

Also see this other thread for some details on how CIM motors heat up when loaded to their maximum mechanical output power.

As many long time FRC participants can attest, CIM motors typically last several seasons unless severely abused. Measuring their free current is an easy way to detect such abuse. Typically that will be about 3 Ampere when first started and will reduce to about 2.5 Ampere after running for a few minutes -- friction reduces a bit when the bearings warm up.

I strongly recommend following the links Richard provided. I've gained a deeper appreciation of motor performance from the graphs, explanations and descriptions by several posters.

Thank you all.

[Patrick Flynn]

Originally Posted by yash101

No. I did read that post. I just haven't replied to it yet. We have a versa-planetary gearbox. I believe that those are built for motors like the BAG motors. It could be side-loading, but that wouldn't cause motor problems because doesn't the typical gearbox separate the motor from the drive-wheel?

Could you please provide more information about where these motors were used and what the loading set up on them was so that we can understand what went wrong here and be better able to understand at your failure?

[Chris_Ely]

Originally Posted by yash101

They were shooter motors running at free speed for maybe 10-20sec, with sudden loads (frisbees being shot)! We used two BAGs. I think some of them got shorted and others had their bearings broken. I think this was all because of poor design because 14000 RPM seems like it would cause arcing in a brushed motor!

Do you have any evidence to back up your arcing claim? Many brushed DC motors achieve speeds much greater that this, including FRC motors. See the 2013 Motor Performance Data sheet.
If you had you shooter wheels directly attached to the output of the gearbox, I could see the side loads from the discs being shot effecting the motor.

[yash101]

Originally Posted by luckof13

Do you have any evidence to back up your arcing claim? Many brushed DC motors achieve speeds much greater that this, including FRC motors. See the 2013 Motor Performance Data sheet.
If you had you shooter wheels directly attached to the output of the gearbox, I could see the side loads from the discs being shot effecting the motor.

I have a feeling that that may actually be the problem, though it seems unlikely. When a frisbee is being shot, it will put a force on the wheel, causing the motor to be sideloaded. That was partially our design, because the compression in the disks helps push them get accelerated better!

Anyways, I (and many others) are done with talking about THIS bag motor failure!

[Al Skierkiewicz]

CIM motors do last a long time if they are not abused. However, the brushes do wear and produce varying resistance to case. Do not be surprised to measure a 2K to case. I have taken some apart and cleaned the dust around the brush assembly. While apart we also added some oil to the bearings.
Do not believe that simply mounting a motor to a gear box will eliminate loading problems. I have seen more than one motor damaged by improper mounting to a transmission. Also, depending on design, a severe side load on a transmission can translate to the motor shaft.
The good news, a CIM smells really bad when it has been abused. Take a good whiff at each end of the motor. If it smells burnt, don' trust it. A CIM motor that has been abused and shorted some windings will have less power output and lower free speed. There are several other failures that occur if you follow the links above.

[DampRobot]

Originally Posted by MikeE

I strongly recommend following the links Richard provided. I've gained a deeper appreciation of motor performance from the graphs, explanations and descriptions by several posters.

Thank you all.

Agreed. Richard's engineering analysis is one of those great resources that turns CD into a place where you can find quality, true, scientifically derived information. Thank you Richard!