Modifying CIMs to implode?
 

OK, so this question in the Q&A system has me intrigued:

The answer from FIRST has not been posted yet, but it has me wondering - is any team actually contemplating turning down the outer walls of the CIM housing? Does anyone expect to be able to remove any meaningful amount of weight without destroying the characteristics of the motor? This would seem to be a very bad idea in terms of maintaining the structural integrity of the motor, and a potential hazard. Or am I being overly conservative? Anyone have any thoughts about whether this should be/will be permitted?

-dave

Re: Modifying CIMs to implode?
 

That's about as bad as "Can we drill holes in our pneumatics to save weight?"

Can't possibly see how FIRST will allow this

Re: Modifying CIMs to implode?
 

Although I'm not one for the mechanical aspect of things, I have to agree with you, it seems like a hazard.

Re: Modifying CIMs to implode?
 

Teams have done it a small amount before to remove the black paint and have a shiny finish.

Re: Modifying CIMs to implode?
 

I agree that it will probably should not be allowed, but wondering what rule they might use to justify a "no, you can't do that" response.

Re: Modifying CIMs to implode?
 

Going from questions similar to this in the past... it would seem to be legal... because it specifies that you cannot modify the internal electronics of the motor, but you can modify the housing... hrmm... maby this is one of those times where they give you enough rope to hang yourself.... because as the steel was removed it would also mess with the magnetic flux inside the motor and probably lower efficiency, similar to removing the metal band on the FP motors.

Re: Modifying CIMs to implode?
 

It might be legal with how the rules are currently stated, but Jeff's example of 2003 and 68 also read that their robot would be legal (or in a grey area, at the very least) until FIRST specifically outlawed it.

I think this would be a similar case, given that it would be a safety hazard and just plain dumb

Re: Modifying CIMs to implode?
 

What if they want to change the material of the housing rather than make holes in it and destroy it's structural integrity, although neither are worth the trouble. If you want to loose weight I am sure there are plenty of other places where you can loose it.

Re: Modifying CIMs to implode?
 

This has been done. I remember very cleary seeing shiny CIM motors on 190's bot last year. I asked a friend of mine who was on the team why the CIM motors looked so skinny. He pointed out that <R31> allowed for modification of the motors structurally, not electrically. I agreed that it was legal, but wasn't sure if it was worth it. I forgot how much weight they lost with this. Obviously, they competed with them, so if anyone questioned the legality of the modified motors, it didn't go anywhere.

My guess is that FIRST will allow it, again. Of course, my preference would be to just not use all 4 of those heavy guys, but alas..

I don't like heavy stuff.

-Andy A.

Re: Modifying CIMs to implode?
 

I have to go with what Dave and Cory said. Its hazardous.

-Arefin.

Re: Modifying CIMs to implode?
 

Maybe the reason why FIRST "allowed" it is because they did not know about it. If you look at one of the rules [the number escapes me now] you can not modify the integrity of a motor. This means you cant modify it physically or electrically. You can remove the gearbox on the fisher price motor and globe motor or alter them as they are not considered integral this year. But if you try to "skin" a CIM motor i would suggest you to have extras as many inspectors this year should have you to replace it.

Re: Modifying CIMs to implode?
 

To answer the above post, let me cite R31, which says nothing about the integrity of the motors:We are modifying the housing, not integral moving parts.

The weight loss was not terribly significant (around .1 pounds), but it helps with heat dissipation. Just make sure to put some clearcoat or paint on them after turning them down, as unprotected steel will rust.

Re: Modifying CIMs to implode?
 

My guess is the answer will be NO modification of motors is allowed. I do not think that they can save enough weight to make it practical to turn down the case, the majority of the weight is in the armature, shaft and magnet assy anyway. My guess is the case is about as thin as it could be now, the company is afterall, trying to make a profit and have already made the determination as to the minimum material the case needs. If the answer comes back that the case can be modified, I can tell you we will experiment with case mods just to be sure that there is no real advantage.

Re: Modifying CIMs to implode?
 

While you're right that the weight savings aren't significant, R31 seems to clearly state that modification of the housing is okay, as ahecht pointed out above. Do you have a counterpoint from the rules that would indicate why a team couldn't do this if they really, really wanted to?

Re: Modifying CIMs to implode?
 

You could probably remove the paint easier with sand paper, if that was your goal.

Re: Modifying CIMs to implode?
 

Yes, but it wouldn't have that hot-off-the-lathe shiny look then.

Re: Modifying CIMs to implode?
 

Has anyone tried any other modifications to help heat dissipation? Are there any places you can safely put holes in the casing to get some air flow inside?

Re: Modifying CIMs to implode?
 

The CIMs have a waterproof outer coat (black) by removing the coating it allows the motor to cool without the insulation of the hard rubber coating. Tyler Forbes on 190 was on my team for a number of years back in high school, and did battlebots for a number of years....a lot of people who used them turned them to save that fraction of weight, and allow for cooling....

Apparently since 190 did it...FIRST probably never had an issue...its that grey area we need to worry about...

Re: Modifying CIMs to implode?
 

Hmm well I'll be waiting to see the reply to this question. I have been wondering about strapping some aluminum oil filter heatsinks onto the CIM motors for cooling. And turning it down or sanding off the paint would certainly help with thermal conductivity.

http://www.jcwhitney.com/autoparts/P.../p-298/c-10101

Between those and a 120mm fan by each transmission, that should help keep the CIMs cool

Re: Modifying CIMs to implode?
 

That's a good idea, and better than nothing, but that mainly cools only the casing. The internals are still pretty hot, and by the time the casing is hot, they're VERY hot.

Still, like I said, any cooling is better than none

Re: Modifying CIMs to implode?
 

I'll defer to any thermal analysis guys, but doesn't a black body radiate heat more efficiently than a shiny aluminum surface?

Re: Modifying CIMs to implode?
 

I believe I have heard that black colored things generally radiate heat better, too, but there are much more important issues here. The paint-metal interface, and the paint itself probably conducts and radiates heat much worse than metal regardless of the color.

Re: Modifying CIMs to implode?
 

Contrary to intuition, shiny bare metal can often be closer to a "blackbody" than black paint. Some black paints are highly IR reflective, which generally means they are not that good at emitting IR when hot.

Re: Modifying CIMs to implode?
 

I think team update 5 sufficiently answered this question.

Re: Modifying CIMs to implode?
 

Yeah, I think that makes it pretty clear: turning down motor housings to reduce weight => bad idea.

On a related topic, it is also a very bad idea to drill into the ends of the housings on the CIM motors, and through the permanent magnets, to open up a flow path to force air through the motors. This is considered a change to the "electrical system" of the motor (i.e. altering the magnets) and is a violation of <R31>. And to the teams that said "don't worry, the inspectors will never notice, and we will get away with it," you are wrong. The inspector-trainers have been alerted. I hear that the inspectors will be on the lookout for this - particularly at certain regional events.

-dave

Re: Modifying CIMs to implode?
 

For those who have not read the update (Why Not!?!)
<R31> So that every robot’s maximum power level is the same, the motors in the kit may
not be modified except as follows:
• It is acceptable to modify the mounting brackets and/or other structural parts
of the motors (output shaft, housing, etc.) as long as the electrical system is
not modified and the integral mechanical system of the moving parts
(bearings, bushings, worm gear output stages, etc.) is not changed or removed...


The intent is to allow teams to modify mounting tabs and the like, not to gain a weight reduction by potentially compromising the structural integrity of any
motor.

As Dave pointed out above, drilling through the magnet to allow air flow violates this rule. Have you thought about what you are doing when you drill through a magnet? You are reducing the amount of magnetic material and therefore the field strength, thus reducing the output power of the motor. In addition, I have not yet seen a magnet that will drill without chipping which makes the reduction in field even worse. Occasionally, this type of abuse has been known to kill the field altogether.(vibration, chipping and cracking) You could drill through the case where there is no magnet but unlike the FP or drill motors, there is no internal fan to move the air.
BTW, I think I might be inspecting again this year and I will look for holes.

P.S. Can everyone quote the rule they are referring (from now on)to so we don't have to open a new browser window to see the reference?

Less weight = less torque...
 

I strongly urge folks not to mess with the steel in the can of the Chiaphua (CIM) motor.


The metal thickness of the motor housing is part of the magnetic path of the motor. There are times when we actually ADD material around a motor to increase the torque of a motor (note the flux yoke on the Fisher Price motors). For some PSD motors, we can get about 15% more torque by simply putting a thick sleeve of steel around the outside of the motor can.

Reducing the motor can thickness on the CIM motor will almost certainly reduce the torque of the motor.

This is one of those happy cases where it is both illegal and bad engineering to remove metal.

Joe J.

P.S. as a rule of thumb, if a large paper clip can be picked up by using the outside of the motor can, it is likely that it could benefit from an external flux yoke, the stronger it sticks the more likely a benefit can be had.

Re: Modifying CIMs to implode?
 

The odd thing is that a teams has all ready done this. In fact this was the only arguement my friend had for saying this. I will ask him what team it is again though. I honestly feel it's a bit dumb but he said almost two pounds of weight can be lost. Anyway I feel it is a moot point because the question has been answered.

Re: Modifying CIMs to implode?
 

See this reply, in this thread: http://www.chiefdelphi.com/forums/sh...5&postcount=12

Two pounds?? As Ahecht pointed out in the above post, the weight loss was not very significant.

Re: Modifying CIMs to implode?
 

I am not going to test the rule or disrespect the advice of motor techs on this list. My follow up is in regards to the reported gain in radiational cooling by removing the black paint by sanding to the bare metal?

Our team has never modified a motor or mount but the comment about bare metal verses paint is of mild interest. Does this violate the rule or even the spirit of the rule? I would guess that one could even add paint to the housing as part of some color scheme on the robot...

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