Re: Modifying CIMs to implode?
 

they might as well try machining 1/32" off all of the pwm prongs on the controller, and while at it, lets shave off the insulation on the wires, thats got to be half a gram right there

:D

Re: Modifying CIMs to implode?
 

Andrew,
I think the rule is clear that removing the paint does not change the basic ops of the motor. But like I have said many times before, if the Chalupas (or any motor) are overheating they are a symptom not a cause. Hot motors indicate a problem somewhere else. Fix the problem. When the case of the Chalupa is hot, think what the temp might be inside at wire level.
When the case is too hot to touch, you have already sacrificed molten varnish to the electrical gods. There is no coming back from this abuse and no amount of external cooling is going to save the motor. The internal temperatures, melt the varnish insulation, run the lubricant out of the bearings, distort the armature plates and shaft, and breakdown the internal adhesives used to keep all the parts in alignment. Remember that the only conduction path from armature to outside world is the shaft and bearings. All other cooling is by convection or radiation which is a slow process.

Re: Modifying CIMs to implode?
 

i know this is off topic, but last year we had drill motors running to a custom gear box (like many other teams). After each round we had 2 of the 120mm fans blowing on the motors because they were almost too hot to touch. My question is, are the CIM motors as likly to get that hot? We are currently being held up by electronics problems, and we have no way to run one for 3 minutes and take the temp. Sorry if that was confusing, i know it was poorly worded.

TIA

Re: Modifying CIMs to implode?
 

It takes a lot longer for the CIM's to get noticeably hot than it does for the drill motors.

Re: Modifying CIMs to implode?
 

Regarding the potential use of the Chiaphua motors as small space heaters, you may want to go back and read through this thread for some interesting observations. Within certain limits, you can expect the Chiaphua motors to experience a reasonable degree of heating during normal use. But at some point, "reasonable" becomes "way the heck too hot." The exact conditions under which this transition occurs is not precisely known, but passing the transition point is dramatic and irreversably damaging to the motor.

-dave

Re: Modifying CIMs to implode?
 

If your CIM's are getting too hot, consider the obvious, your gearing is too low. If heat is a problem, the motors are working too hard. If you properly gear your drive train too run at the motors max RPM you should have no problem with overheating.
Good Luck!

Re: Modifying CIMs to implode?
 

I think you mean high... if your robot is geared low, it would mean it's very slow, which means it's harder to stall the motors, which creates heat.

Or maybe I interpreted what you're saying entirely backwards

Re: Modifying CIMs to implode?
 

I'm sorry if I mis-spoke regarding the gearing being too high /low. What I was trying to say is, if you gear your drive train to run the motors at max. RPM they are less likely to overheat because they are under less load. We competed in three regionals and the nat's and never once had a heat problem with the CIM"s Just trying to be helpful, nothing else.
Good Luck!

Re: Modifying CIMs to implode?
 

The CIMs are pretty tough when it comes to abuse, now that I think of it.

Last year, against my advice someone decided that a 4:1 ratio on the CIMs would be enough for the drivetrain :ahh: Well to their (the motors) credit, they did move the bot around, but after 7 minutes or so of driving around. You could smell some not so pleasant smells coming from the motors. So we added on some more sprockets and got it down to 13:1 or so.

Oh well, live and learn, then learn to use the datasheet. *sigh*

Re: Modifying CIMs to implode?
 

I will just chime in to say that I'm not to concerned how hot motors are after X number of minutes of drive time during practice. Only how hot they are at the end of 2:15 minutes. If they are a little toasty but not to hot to touch, then We've got fine gearing as far as motor health is concerned. Anything after that is just a sign to me that I could get a little more speed from them if I used some taller gearing. As long as the bot turns and the motors are not fried, go for some more speed if that fits your game plan.

Remember- These machines only have to run for about 2 minutes at a time. It doesn't do you much good to make it more efficient or reliable then it has to be. We all have the same power available, the teams that win are often the ones that squeeze every last watt they can from the motors. If that means heating the motors up more then they were designed for, I can live with it. I'd rather sacrifice a motor every now and then then sacrifice a function.

Which makes me wonder if running this years FP motors at 12 volts is really worth it. I'm still not sure. 407 is such a lovely number...

My how his thread has wondered. My apologies for pulling it further off topic.

Re: Modifying CIMs to implode?
 

Heat=wasted energy
Whether this heat comes from excessive current or friction, you are wasting energy. Max efficiency looks to be in the 4000 to 5000 RPM for the Chalupa motor at about 75%. That means 25% of the current is going into heat. Running it outside those speeds where efficieny drops off to say 50% and half of your current is going into heat, multiply that by four motors if you are using that type of design and you are throwing a lot of power away heating up the playing field. (i.e. you have designed for max output power, fully 350 watts per motor are turning into heat.) With six robots running on the field, matches are likely to occur far more frequently than anytime in the past. This is the year for efficient designs.

Re: Modifying CIMs to implode?
 

On a related topic, R31 states that you can modify the output shaft. We need to increase the length of the keyway a bit. Our first thought was to remove the face plate and add a bit of keyway, not back past where the faceplate would be replaced, but close to the plate. Two questions:

1) Would this be illegal (I do not think so, as we are only taking to motors apart to ease in a legal modification, and

2) Does anyone know if the motors are brushless or not? (i.e. will they be a nightmare to reassemble)?

~ Christopher

Re: Modifying CIMs to implode?
 

Taking apart the motors is not illegal, assuming you don't modify the internal parts. However, you should take care when doing so. The motors are not brushless, and when you take the motors apart, it is possible that you will shift the orientation of the brushes with respect to the field magnets, which would either advance or retard the timing (making the motors run better in one direction or the other). However, it should possible to realign the motors when reassembling them either by ear or with an optical tachometer.

Re: Modifying CIMs to implode?
 

It would make sense to disassemble to make the mod. It is also legal in my opinion to do so since you are not modifying internals parts.
The motors are not brushless, however. The brushes live in the end where the wires enter the case. They are pretty decent size but you cannot affect brush timing if you take it apart. The trick is getting the motor back together. I am assuming you want to get the armature out of the housing to work on it. If you have never disassembled a brush motor, I would not recommend you try now. There are certain techniques you need to follow to keep from killing the brushes or something worse.

Re: Modifying CIMs to implode?
 

While taking the motor apart to machine a longer keyway in the output shaft is not against the rules, it is probably a bad idea. I seem to remember a lengthy post from Joe Johnson when the Chiaphuas were first introduced, in whichh it was VERY strongly recommended that you do not disassemble the motors. When the armature was removed from the magnetic field and then reassembled, he found that they lost a significant amount of power (I seem to remember something on the order of 15-20%). Unless you really know what you are doing, and know how to properly use keeper bars, etc. to maintain the field stregth, then you should probably leave the motors intact.

-dave