Compressed air for rapidly cooling motors?

[Knufire]

Originally Posted by aphelps231

To clarify, I'm mostly referencing the second finals match of IRI in 2014, towards the end of the video you can see members of 254 spraying their motors with what looks like compressed air, in order to super cool their motors for the next match.

Motors or breakers?

http://www.chiefdelphi.com/forums/sh...d.php?t=131409

[aphelps231]

Originally Posted by Knufire

Motors or breakers?

http://www.chiefdelphi.com/forums/sh...d.php?t=131409

Motors.

Breaker isn't an issue for us since we're not running a 6 CIM drive base (although I wish we did).

[GreyingJay]

Somewhat related question about CIM heat:

The first day we did a drive practice session, we kept going and going and going, swapping out batteries as needed. Nobody was thinking too much about motor heat or letting the robot rest. Eventually we noticed the smell. Someone described it as smelling like yoghurt. I ascribe it to burning plastic. Knowing where it was likely coming from, we turned our robot upside down and, sure enough, the four CIM motors were extremely hot.

At what point has irreparable damage been done? I assume the fact that I can smell plastic is not good news, but the robot still seemed to drive fine after being given a cool down period. This suggests to me that windings have not melted or shorted appreciably.

We will probably want to test the internal resistance of the motors once the practice bot is eventually disassembled.

[Ether]

Originally Posted by GreyingJay

At what point has irreparable damage been done?

Here are some quick tests you can run to assess the performance degradation.

Make a test rig using a well-assembled, lubed, and broken-in dual-motor gearbox with an encoder. And set aside a known-good CIM (I'll call it the "reference CIM" with its leads soldering together. Keep this test rig for future testing and CIM evaluation.


1) Put the suspect CIM in the gearbox, apply full voltage, and measure the free speed.

2) leaving the suspect CIM in the gearbox, add the reference CIM (with leads soldered together) to the gearbox. Apply full voltage and measure the speed.

3) If you don't already know approximately what results you should be getting, remove the suspect CIM and repeat steps 1 and 2 using a known-good CIM.

[Alan Anderson]

Originally Posted by GreyingJay

At what point has irreparable damage been done? I assume the fact that I can smell plastic is not good news,...

The lasting damage on many motors is when plastic brush holders soften and stop holding the brushes in place reliably. If you can smell plastic, I would call it toast.

[GeeTwo]

Originally Posted by Ether

.. add the reference CIM (with leads soldered together) to the gearbox ...

I'd like to suggest a simple tweak (based on an Ether post in another thread). Instead of soldering the reference CIM leads together, simply attach and disconnect the wires; this will allow you to leave the reference CIM in the gearbox all the time. As this is likely to carry significant current, a regular switch is probably not the best way to do this. I would put a power pole connector on each lead (probably both in the same oddball color so I knew this was my reference CIM), and connect/disconnect them to short/open the motor.

[Dunngeon]

This should help answer your question.

[aphelps231]

Originally Posted by GreyingJay

The first day we did a drive practice session, we kept going and going and going, swapping out batteries as needed. Nobody was thinking too much about motor heat or letting the robot rest. Eventually we noticed the smell. Someone described it as smelling like yoghurt. I ascribe it to burning plastic. Knowing where it was likely coming from, we turned our robot upside down and, sure enough, the four CIM motors were extremely hot.

We learned a similar lesson about motors and gearboxes after our first district this year. We used to have a four bar linkage with a U shape on the top formed by two prongs on the driver and follower arms, and the coupler link (I have a close up of the arm in our reveal video). Given how tricky the arm was to operate at our first district, we decided to take it off. Before we had gotten to removing the arm, the drive team was practicing with the robot and ended up burning out the Mini CIM attached to it because one of the limit switches had failed. After removing the arm, doing a bit of research, and testing the arm again, we concluded that the motor had gotten so hot that it boiled (or just heated to a high temperature, I was in the shop when this happened) the lithium grease inside of the Banebots gearbox it was attached to.

Long story short, cooling CIMs is probably a good idea in between tight matches, and CIMs are tough motors, they're pretty hard to burn out.

[tickspe15]

Originally Posted by aphelps231

it was a common belief (on 1318) that super cooling CIMs was bad for them

It was? How did I miss out on a common belief?

We didn't have a problem with motors or the main breaker getting too hot in 2014 with the exception of the compressor and everything at long outreach events. The drive train was geared very conservatively (4cims 10.71:1 w/4" wheels)

Teams sometimes cool motors to get a little more performance but I havent seen any data as to how effective this is over such a short amount of time. The big thing in 2014 was cooling main breakers as they are triggred by temperature

[Al Skierkiewicz]

OK,
So there is some common myths here that rear their head every few years or so.
The CIM motor heat is for the most part due to resistive losses in the armature and to a lesser extent, the friction caused in the shaft bearings and the brush assy. Teams who try to cool the exterior of the motor do not remove this heat and as Don has pointed out, shocking the ceramic magnets can lead to a shattering risk. Those parts of the magnet that will break off will lodge between the magnet and the armature. Also rapid heating/cooling will reduce the magnetic fields in the magnets. This will not be apparent for many teams but I have experienced it in motors that require a specific output power for the work they are doing. (video head motors and capstan motors on tape machines for instance)
Teams who use the cooling spray method generally have searched around for the best cooling ability. There are circuit cooler sprays that are available that do use fluorocarbons. While these do produce a lower temperature, the heat still internal to the motor is not removed. It is pretty easy to see that spraying with these products cause ice to form on the surface that will rapidly melt and produce condensate on the surfaces that have been treated. They simply cannot remove enough heat to be effective.
Yes teams also spray the main breaker, but in this case there simply is not enough thermal mass inside the main breaker for this method to be effective.
Additionally, the fluorocarbons used are also solvents. To spray them on devices that are not sealed will cause lubricants to be washed out. Luckily, the CIM shaft is closed on one end and normally behind a transmission case on the other so very little of the solvent enters that motor. There are also rubber seals on the two ends plates. It does however, work it's way into other motors like fans, and servos, and wheel bushings and bearings.
While we are on the subject of internal motor heating, many of you are using the 775 motor and others like it. Please note that there are vents at both ends of the motor as well as slots on the side. This motor has an internal fan that pushes air out the side slots. It must pull air through the slots in the end of the motor to cool the armature. If you mount this motor on a planetary gear box without using the slotted adapter plate, the armature of the motor will get hot as no air will be pulled in from the shaft end of the motor. Additionally, if you running this motor at a slow speed, the fan is not running at an efficient speed to move cooling air through the motor.

[Jon Stratis]

I did see something new at North Star yesterday... not compressed air, but a team had what looked like trash bags full of ice they placed on their drive motors between elimination matches to try to cool them down. Fortunately, I don't think they suffered any leaks!

[Everett33]

If anybody took a lap of the pits at Troy, they would have seen this interesting tidbit of information.

https://www.flickr.com/photos/131241...7666788511116/

- Everett

[Al Skierkiewicz]

Everett,
Did you see this robot? Can you tell me what they mean by hollow bolt/active cooling?

[Richard Wallace]

Originally Posted by Al Skierkiewicz

Everett,
Did you see this robot? Can you tell me what they mean by hollow bolt/active cooling?

Isaac Rife (IKE) may already know about this. If not, I'll have a look when I see 33 at MSC in few days. The team is generally very forthcoming about the cool features embodied in their robot.

[BJC]

First off, Aren Hill deserves all credit for this idea.

Basically, the mounting holes for a CIM type motor are the only access points to the inside of the motor. For reasons described earlier cooling is much more effective when air is forced directly past the armature. When you put 2 and 2 together you end up with hollow fasteners. I'll leave the rest as an exercise to the reader.

Cheers, Bryan