OK, so this question in the Q&A system has me intrigued:
Q 1330: Under the restrictions specified in , is it permissible to turn down the housing/case of the CIM motors to reduce weight?
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?
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.
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
Q 1330: Under the restrictions specified in , is it permissible to turn down the housing/case of the CIM motors to reduce weight?
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.
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…
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.
To answer the above post, let me cite R31, which says nothing about the integrity of the motors:
[list=1]
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.
[/list]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.
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?
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?
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…
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.
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