Modifying CIMs to implode?

[Al Skierkiewicz]

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.

[jgannon]

Originally Posted by Al Skierkiewicz

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.

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?

[tkwetzel]

Originally Posted by sanddrag

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

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

[ahecht]

Originally Posted by tkwetzel

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

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

[Greg Perkins]

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...

[ConKbot of Doom]

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

[Cory]

Originally Posted by ConKbot of Doom

Hmm well I'll be waiting to see the reply to this question. On 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 pain 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

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

[Bruce C.]

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

[Max Lobovsky]

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.

[Alan Anderson]

Originally Posted by Bruce C.

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

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.

[Joe Ross]

I think team update 5 sufficiently answered this question.

[dlavery]

Originally Posted by Joe Ross

I think team update 5 sufficiently answered this question.

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

[Al Skierkiewicz]

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?

[Joe Johnson]

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.

[M. Hicken]

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