Does motor temp affect performance?

[Alex_Miller]

This is more of a side note and won't fix the overheating issues, but may help you get better performance from your drivetrain.

I've heard that if your wires are longer than they need to be then the resistance of the wires can start to affect the voltage (at high amp conditions like pushing match) that the motor is receiving by a decent amount and cause you to not preform as well.



If you do add a heatsink and it doesn't work as well don't forget to try it with thermal paste.

[Alan Anderson]

Originally Posted by Ether

Yeah, a fan is probably the first thing to try.

But the converse is true too: with or without fan-forced airflow, surface area is key.

In this application, a fan is definitely the first thing to try (assuming you don't have a mechanical issue that is causing the heat problem to begin with).

If you don't have airflow, you're relying on radiative cooling, and in that case surface area is very important. But in order to get enough radiative cooling to make a significant difference, the motor has to be hot enough that it will likely already be permanently damaged.

[Ether]

Heatsinks work best with forced airflow. But they also work without fan-forced airflow. The large surface area creates convection airflow. When the robot is moving, the resulting airflow also helps.

Has anyone here ever done a comparative evaluation of fan-only vs heatsink-only vs heatsink-plus-fan on a CIM motor? Would be nice to see the data.


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[dtengineering]

I can't think of a rule that would specifically prohibit a bit of dry ice being used to cool a motor. In fact, I've thought, from time to time, that it would be interesting to wrap the CIMs in custom dry ice cooling boxes and keep them super-chilled for the duration of the match.

But we have yet to be disappointed with CIM performance in normal, uncooled, use, so it's a pretty low priority. Not to mention the sort of thing that I'd want to clear on the Q&A first.

Alternatively, an ice filled aluminum mold that fits over the CIMs might work between matches, without the need for aerosols.

I think the best advice, however, is to see if the gearing or gearboxes can be adjusted to reduce current draw... perhaps a better off-season project than a Thursday morning in Atlanta project.

Jason

[Ether]

Originally Posted by dtengineering

I think the best advice, however, is to see if the gearing or gearboxes can be adjusted to reduce current draw... perhaps a better off-season project than a Thursday morning in Atlanta project.

It would be most interesting if teams experiencing hot CIM motors could provide some information about their robot design.

In the case of CIMs used for driving, that data might include ratio of gearbox, sprocket teeth count if using chains, how many CIMs (2 or 4 or ?), and wheel diameter and type of wheel.

[Tristan Lall]

Originally Posted by Ether

FWIW:

http://www.vapco.com/prod_freezeitspray.html

Freez-It contains menthol, camphor, eucalyptus oil, and isopropyl alcohol.

Menthol, camphor, and eucalyptus oil are mostly harmless in small amounts, but have a strong odor. Same ingredients are in Vicks Vapo-Rub that Mom used to rub on your chest when you had a cold (oops, am I showing my age?).

Isopropyl alcohol, unlike ethyl alcohol (the drinking kind) is toxic if ingested or inhaled in sufficient amounts. If you get an unexplained headache that should be a warning sign.

Get enough folks using that indoors and it may get banned. Although I suppose the venue at Atlanta is large enough it might hardly be noticed?

I don't think that's the stuff Joe was thinking of. (That Vapco product is not an appropriate substance to be using within a motor.)

The correct stuff is based on various fluoroethane compounds.

MG Chemical sells a product that works well for this purpose. In fact, I think I've seen 47 using exactly this product, many years ago. 188 has also used it to good effect (primarily in the days before 120 A circuit breakers and CIM motors).

In a pinch, an "air"-in-a-can duster, inverted so that the liquid is released, will work as well (they're generally composed of the same chemicals).

[big1boom]

Originally Posted by Tristan Lall

In a pinch, an "air"-in-a-can duster, inverted so that the liquid is released, will work as well (they're generally composed of the same chemicals).

Last year we had CIM heating issues. We were running one CIM for the entire drivetrain so we were asking a lot out of the motor. To combat the heating we used an inverted air duster. Any brand will work, but I recommend getting one that does not have a bittering agent.

[Al Skierkiewicz]

Originally Posted by Alex_Miller_2175

This is more of a side note and won't fix the overheating issues, but may help you get better performance from your drivetrain.

I've heard that if your wires are longer than they need to be then the resistance of the wires can start to affect the voltage (at high amp conditions like pushing match) that the motor is receiving by a decent amount and cause you to not preform as well.



If you do add a heatsink and it doesn't work as well don't forget to try it with thermal paste.

I would think that the dry ice would tend to freeze the lubricant in the sleeve bearings on the CIM prior to a match. You might just raise the current from the added mechanical resistance. Unknown what the expansion/contraction of the various parts under these severe conditions would be. However, bronze inside of cold aluminum around a steel shaft seems to send chills down my spine.

[Damaku250]

Originally Posted by Ether

It would be most interesting if teams experiencing hot CIM motors could provide some information about their robot design.

In the case of CIMs used for driving, that data might include ratio of gearbox, sprocket teeth count if using chains, how many CIMs (2 or 4 or ?), and wheel diameter and type of wheel.

- 6WD powered by 4CIMs through AM Toughboxes
- 6" Plaction wheels with roughtop tread
- roughly 18:1 gear ratio from CIM to wheel

however, we have a plywood tray holding our pneumatics, roughly at the base of the toughboxes, and a plywood electronics board practically sitting on top of it. No way to avoid it, as we're a tunnel bot.

Pictures here:
http://i298.photobucket.com/albums/m...e399f66d76.jpg
http://i298.photobucket.com/albums/m...5f2f2a56_o.jpg
http://i298.photobucket.com/albums/m...cfa3da23_o.jpg

[Al Skierkiewicz]

Hey Craig,
All six wheels on the ground? You have trouble turning quickly?

High friction wheels on carpet in turns causes high (and I mean very high) currents in CIM motors. Assume that the CIMs are going into stall every time you turn. I bet it would not be unusual for the CIMs to be running at 100 amps in turns, each. 100 amps means about 1200 watts per motor, all things being equal. Yes that is like four 1000 watt light bulbs in your robot making heat. The fix is changing the height of the center wheel, change some of the wheels to omnis or a combination of the two.

[Damaku250]

Originally Posted by Al Skierkiewicz

Hey Craig,
All six wheels on the ground? You have trouble turning quickly?

High friction wheels on carpet in turns causes high (and I mean very high) currents in CIM motors. Assume that the CIMs are going into stall every time you turn. I bet it would not be unusual for the CIMs to be running at 100 amps in turns, each. 100 amps means about 1200 watts per motor, all things being equal. Yes that is like four 1000 watt light bulbs in your robot making heat. The fix is changing the height of the center wheel, change some of the wheels to omnis or a combination of the two.

No, we have a dropped-middle wheel design

[Al Skierkiewicz]

Craig,
You have to be more specific. How much is it dropped? How many wheels are actually touching the carpet, how many in turns? How heavy is your robot? What is the final ratio? etc.

[M.Wong]

As a side note, I would check out the victor/spike/jag going to a hot motor. Last year we had a malfunctioning victor that was rapidly switching from full forward to full backward, causing our cim to be scorching hot.

[Ether]

Originally Posted by M.Wong

Last year we had a malfunctioning victor that was rapidly switching from full forward to full backward

May I ask how this was diagnosed? Seems like a very odd failure mode.


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[sanddrag]

I've machined an aluminum heat sink for a CIM, and installed it with thermal paste. I think it had about 40 fins, about 3/16" wide, but only about 1/8" tall. It was the length of the motor. Didn't make any appreciable difference in temperature after running. I installed a high-flow fan pointed straight at the back of the motor (directed along the length of the fins). Didn't make any appreciable difference. I was running the motor under a constant load that made it draw about 25 amps continuous. Within 4 minutes, it was time to stop and cool for 10 minutes.

The heat comes from the windings within, with not a lot of ways out. Time, and dropping the temperature of the surroundings (endbell especially) is the only thing that will cool it sufficiently.