CIM Motors reusable?

[Patrick Flynn]

Originally Posted by jeremy callahan

we also had some issues with the bag motor. they ran great at the beginning but at the end of the day you would have to resort to "kick starting" the wheel to get it up to speed. If we could figure out how to stop having to "kick start" it we would like to use them. But we just don't want to have to rely on that in the middle of competition. That's our opinion on them.

Could you provide some more info here?

When you say ran worse at the end of the day was this a competition day with ~2 minute matches being run or a testing day where the motors were run much more continuously?

In either above situation was a motor cool down period allowed?

After experiencing these required "kick start" were the motors replaced or did the issue not appear at the start of a 'new' day?

What was the use of these motors and the expected loading?

[FrankJ]

The some of the bag motors had a manufacturing issue with the brush assembly. It was documented with the fix on team update 2013-04-09.

[JVN]

Originally Posted by jeremy callahan

we also had some issues with the bag motor. they ran great at the beginning but at the end of the day you would have to resort to "kick starting" the wheel to get it up to speed. If we could figure out how to stop having to "kick start" it we would like to use them. But we just don't want to have to rely on that in the middle of competition. That's our opinion on them.

Hi jeremy callahan,
There was a documented manufacturing defect which affected some BAG motors. We at VEX/IFI worked very closely with FRC teams, our motor manufacturer, and FIRST to identify the problem and provide a retrofit to teams.

http://content.vexrobotics.com/vexpr...s_20130411.pdf

In addition, we've ensured that this problem will not happen moving forward. 100% of BAG motors in our warehouse have been retrofitted, and ALL of them were dyno tested in-house to ensure performance within 10% of our published spec. (It turns out, all of them were within 5%.)

If any team experiences a problem with a BAG motor, I hope they will immediately contact our customer support team by emailing prosupport@vex.com or calling 903.453.0802 We pride ourselves on our customer support, and want to "make things right" if you have an issue.

-John

[JVN]

Originally Posted by yash101

Our shooter BAGs kept failing. We took a couple apart and the bearings were shattered, and looked partially burnt!

yash101,
I'm sorry to hear your team had BAG motors fail. Did you contact our customer support group?

If any team experiences a problem with a BAG motor, I hope they will immediately contact our customer support team by emailing prosupport@vex.com or calling 903.453.0802 We pride ourselves on our customer support, and want to "make things right" if you have an issue.

Based on some of the other comments in this thread, it sounds like it might have had something to do with your application, but of course we'd be happy to talk it through with you and your team.

If you suspect there is some problem with the BAG motor in general, we want to help resolve it, or identify what is really going on.

Take Care,
John

[yash101]

Thanks. I'll talk to my team about it. Right now, it isn't too big of a deal anymore. All our other vex products perform the way they should!

[Chris_Ely]

Originally Posted by yash101

Just avoid reusing BAG motors. They don't have a very long lifespan because the bearings get destroyed by the high RPM, (14,000RPM).

Originally Posted by yash101

Our shooter BAGs kept failing. We took a couple apart and the bearings were shattered, and looked partially burnt!

Please avoid making generalizations based on just your experience. Just because you had some motors fail does not mean that the entire line of motors is bad. There are many factors that could contribute to a motor failing such as how you use it. I highly doubt that the designers would use bearings that are rated under the RPM of the motor.

[BobbyVanNess]

CIM motors are the most durable motors allowed in FRC. We've definitely gotten some mileage out of them, and I've never actually seen one go bad. Usually we'll use old CIM motors on our practice bot when we run out of new ones. I've never felt any noticeable difference in power on the drivetrain, where they're primarily used. This past year, a 2008 CIM motor actually wound up on the flywheel for our 2013 competition bot, and it worked absolutely fine all year. Though we made sure to peel the 2008 sticker off at our first regional in case any nosy pit scouts were to take notice

[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.