CIM Motors reusable?

[yash101]

Yeah. That is a good idea. I am not trying to bad-mouth them. As a matter-of-fact, I really think the CIMs are one of the best drivetrain motors!

[Gregor]

Originally Posted by yash101

Yeah. That is a good idea. I am not trying to bad-mouth them. As a matter-of-fact, I really think the CIMs are one of the best drivetrain motors!

Cool. That means you are the 99%.

[z_beeblebrox]

Originally Posted by Gregor

Cool. That means you are the 99%.

http://www.chiefdelphi.com/media/photos/19904

[yash101]

That seems like it will go at 60MPH, carrying 500 pounds

Anyways, what was the free speed of this? Did the robot look like it was moving? I'd like to see that. Bring it to the PHX regionals 2014!

[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.

[Gregor]

Originally Posted by yash101

That seems like it will go at 60MPH, carrying 500 pounds

Anyways, what was the free speed of this? Did the robot look like it was moving? I'd like to see that. Bring it to the PHX regionals 2014!

Let me get this straight, you want someone to bring a nearly 10 year old robot from South Carolina to the 2014 Phoenix regional?

[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?

[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!

[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.

[EricH]

Originally Posted by Gregor

Let me get this straight, you want someone to bring a nearly 10 year old robot from South Carolina to the 2014 Phoenix regional?

I brought that one up a couple weeks back, myself, when he thought that window motors had a lot of power and would be great in drivetrains...

...as a counter-example to show that while it could be done, it was NOT a good idea.



CIMs and their cousins (BIG CIMs from 2006 and 2007, Mini-CIMs, and Bag motors) are some of the most bulletproof motors in FRC, to say the least. I can't think of a single failure of one of those on any robot I've been involved with, even with some pretty hefty abuse. Drill motors, FPs, and BaneBots, I've heard of, particularly when someone abuses them a little bit (or in the event of motor manufacture defect), but very rarely do I even hear about a CIM failure.

[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.

[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.

[Ether]

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.

The information you provided would be much more helpful with further context. Please post details of your shooter design,including:

- how the motor was mounted to the frame and to the wheel

- disk compression

- gear reduction from motor to wheel

- speed of the motor at shooter operating speed

- wheel speed controller (e.g open or closed loop)

- duty cycle (continuous or on-demand)

- pictures would be helpful

- if you have it, motor amps at operating speed

But more importantly: Did you contact VEX, and discuss this with them, and send them the motor for failure analysis?

[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?