CIM's Over loaded/Heated

[merybar]

Trying to see if any of you have any thoughts on this, we are at a loss of what to do. We decided that our belt driven drive with fisher prices were not quite quick enough so we made some modifications. We left our Belt and large pulley on there but attached a sprocket to the back which leads down with a chain to the CIM, with a small sprocket on the CIM (Very small, as small as we can get) We reduced the CIM's RPM's down to about 675 (increased from 120 from the Fisher Prices). Tonight when we finished it up (we are a Michigan team) It ran amazingly without load, and with the trailer and running around it did great, however when we started to hold it up the CIM's Got hot, after about 15 mintues of testing they were smoking hot. (steam was leaving a CIM) So this leads me to the question, any suggestions or ideas to fix the problem? Any ways to cool them off? Thanks everyone,
Matt

[gorrilla]

15 minutes is a loooong time to be running them under load......


ours' never got as hot as you mentioned..but they do get hot....to the point of the PWM's therming out and shutting the off untill they cool down....

and your running them direct drive too...thats probobly most of the cause....

[big1boom]

what kind of load are you putting on the CIM?

CIM's should not heat up that much this year. However, I know for a fact that at least our team had a factory defective CIM. Once we changed it out with one from the spare part's table, we were able to run great for several matches in a row.

the CIM's are able to take a beating, but heating them up to the point where steam is coming off of them is probably not good for them.


I would suggest you try a different CIM, that fixed most of our overheating problems.

[MrForbes]

Sounds like you're probably going to have to live with the drive ratio you have, so just realize that they'll get hot, and only drive for a couple minutes at a time, let it cool for 5 minutes before you drive again.

[merybar]

Thanks everyone,
Yes they did stop working, they would go go go and then after i bit they would slow down, the vic's have a "therming out" function? Thanks for your help!
Matt

[gorrilla]

Originally Posted by merybar

Thanks everyone,
Yes they did stop working, they would go go go and then after i bit they would slow down, the vic's have a "therming out" function? Thanks for your help!
Matt

the PWM's do...I dont know exactly how it works but they do it....

you could try putting some sort of transmission in there.....

[artdutra04]

If you saw "steam" coming off of them, it may be too late.

CIM Motors will smoke and/or die, although they don't always release magic smoke. Once they pass this point of no return, they will continue to function to a certain degree: they'll still spin, but they will be very inefficient at making mechanical motion and VERY efficient as a space heater. So much so, that as soon as you apply power to them under a moderate load, within ten seconds they will be too hot to touch.

As for your application, do you have any pictures of this set up? Did you leave the Fisher Price transmissions on the robot and add a CIM motor in addition to that*? What is the gear ratio between the CIM motor and the output sprocket where it interfaces with the output of the FP?

* If you did this, and the output from the addition of the CIM motor gear ratio is not almost exactly (within a few percent) the output rpm of the Fisher Price transmission, the CIM motor will be back driving the FP. This will waste a huge amount of mechanical power, and would likely lead to an overheating issue.

[Kevin Sevcik]

I second Art's questions/suggestions. From your description of your setup, it sounds like you haven't properly matched the ratios of the CIMs and FPs. If you don't have them well matched, they'll be constantly fighting each other, and it will only get worse the faster you drive them or the more external load you put on them.

You should be striving to match the free speeds of the motors as closely as possible. If I'm reading you correctly, and your CIM free speed is 675 RPM, while your FP free speed is 120 less at 555 RPM... That's entirely too large a difference and easily explains your problems. You need to match the gear ratios much more closely than that.

[MrForbes]

I assumed that you had taken out the FPs, bad move on my part. Pictures would be oh so very helpful.

[merybar]

I should have taken a picture today, ill get one tomorrow for sure, what we did was we pulled off the FP completely and are direct driving the CIM to the chain, i will have to look into the motor tomorrow as well, hope we didnt fry it.
Thanks
Matt

[sanddrag]

A picture will indeed say a thousand words, but we have experienced similar results when running the CIMs for more than 10 minutes or so. We've cooked about four of them over extended practice use, but none during the short runs in competition. I think you just need to give them time to cool off. Also, make sure your electrical connections to the motor are good.

[roboticWanderor]

you could always try a method to help dissipate the heat better, such as a fan, or a DDR2 THERMALTAKE heat sink.....

[R.C.]

Originally Posted by roboticWanderor

you could always try a method to help dissipate the heat better, such as a fan, or a DDR2 THERMALTAKE heat sink.....

Beat me to it, i was thinking about using the heatsinks 1024 used on their bots last year. Heard they worked great, Q can fill us in on this.

[Brandon Holley]

Originally Posted by roboticWanderor

you could always try a method to help dissipate the heat better, such as a fan, or a DDR2 THERMALTAKE heat sink.....

How effective was this?

It seems that clamping a cylinder (heat pipe) to another cylinder (motor), your only going to gain one axis of contact, and your heat transfer will be very inefficient.

[R.C.]

I was thinking more of this:

http://www.chiefdelphi.com/forums/sh...ad.php?t=64613

Read Q's post on the bottom of page.