Cooling Motors


#1

Can we have stored air off the robot, we would have pneumatic quick connectors threaded on the gearboxes to we can easily cool them in the pits


#2

This is one of those questions that has a complicated answer.

I’d say that your basic concept is probably okay, in that you could use compressed air in the pits to cool off motors. I suspect that even the quick connects on your gearboxes would pass inspection (though I’ll defer to the opinion of a RI on that) as long as you’re not doing anything on the field that would violate the motor, gearbox, or pneumatics rules.

Having said that, you’ll have some problems actually pulling this off. The big one is that you’ll have to rely on stored air, not on an air compressor. There is no way that the RIs will allow a separate air compressor in the pits, especially not one larger than the legal robot compressors. We had a hard enough time as a team getting our mini-bandsaw past them, and those are specifically allowed by the rules.

The other big problem is that you’ll be blowing compressed air directly into a gearbox, which might not be such a good idea in the long run. The compressed air will certainly produce condensation unless you have a moisture trap fitted to the tank, and even then you’ll get a bit. Having that mixing with your gear lubricant isn’t really a good thing. It will probably be fine for a time, but eventually it’s likely to cause problems.


#3

We liquid cool our bot by pouring water all over it every 3 matches. Works like a charm


#4

Or you could just use ice packs. You can get a pack of like 12 for cheap at a walmart or something.


#5

My #1 recommendation for cooling motors is canned air. if you flip the stuff over you get a liquid stream not to dissimilar to liquid nitrogen. It cools extremely quickly and is a lot more acceptable to the LRIs and officials than compressed air tanks as you are suggesting.


#6

I think cooling motors in the pits isn’t very restricted.

Putting quick-connects on your gearboxes implies that the gearbox being pressurized will push air through the motors. Assuming you have air cooled motors (750’s), there’s no reason why this wouldn’t work. You’d need to make sure you close off all other openings to the gearbox so the air would actually exit through the motors, and you’d need to make sure you opened those other openings back up when you’re done so the motor can suck-air as it’s designed.

Quick connects do constitute a little bit of extra weight, but if you want it, I think it could be worthwhile.

Some venues don’t have enough pit-power for teams to have 120VAC air compressors and they’ll say that up front.


#7

PLEASE DO NOT DO THIS!

The contents within “canned air” is not chemically similiar to liquid nitrogen. While the refrigerant has semi-similar thermodynamic properties to (l)N2, when passed over large sources of heat, the contents of “canned air” chemically decomposes and is highly toxic which can even be fatal at exposures of minimal concentration. The contents, most often R-134a, is tetrafluoroethane and decomposes to carbonyl difluoride, an analog chemically similar to carbonyl dichloride (phosgene).


#8

Here’s a good solution that isn’t dangerous to people. Also yes, canned air is dangerous and can cause frostbite too.


#9

From what I understand about the chemistry of CF4, its breakdown temperature is high enough that using it for applications under 100 ºC or so won’t cause enough decomposition to pose a health hazard. On the other hand though, it is a potent greenhouse gas. So as I understand, as long as your motors aren’t getting hot enough to boil water, you shouldn’t be in too much danger. Correct me if I’m wrong though, I would hate to give unsafe information.


#10

Here’s the MSDS for CF4 if anybody wants to read it.


#11

Just to be straight, tetrafluoroethane (R-134a) is CH2FCF3 (or C2H2F4) and not CF4 they are two very different compounds.

If your motors are hot enough that you would want to cool them, and that they likely could solidify egg whites on the brushes, then the temperatures are hot enough to chemically decompose a refrigerant.

Speaking as a synthetic organic chemist, refrigerants have very unusual pressure curves when you look at pressure vs temperature, after-all that’s why they work so well to transfer heat between sources. When the tetrafluoroethane exits the can as a liquid it is still under high pressure, otherwise it would be a gas, and can come in contact much more violently with internal components that are are a higher temperature than the surface of the casing. I just would say the risk of using a potentially hazardous chemical when you can just use an ice pack (I wouldn’t use liquid water either as that can leak into the casing and cause corrosion) or push air from your compressor over the surface (but beware not to blow debris into the motor) doesn’t outweigh the return.


#12

I suspect is is very event dependent. We compete in the Ontario Region and have never had an issue bringing and using a compressor at an event. We typically bring a fairly small but still 120 VAC unit, however, I have seen a fair number of the 2 - 4 gallon pancake style compressors at events. Beyond using air guns to “dust” the robot after repair work we have used it to run an air rivet gun.

Don’t see many bandsaws, but we sometimes bring a small drill press and that is a very common sight in the pits.

The only discussions have been around assuring RI and safety folk that we are not charging air tanks with the big compressor.

The Event Rules Manual (section on Machine tools) specifically allows:

Small, bench-top machinery, with appropriate guards, is permitted in team pits. ‘Small’ machinery is machinery that can be easily lifted by one person.

Examples: Small band saws, drill presses, desktop CNC mills, and sanders.

and disallows:

E34. Floor standing power tools are prohibited.

Examples: Full-size drill presses, full-size band saws and full-size table saws.

Having said all that, I would not recommend cooling with compressed air, as there are easier and safer ways to do this.


#13

Personal safety? Psh, whatever.

Here’s the real reason not to flip the air duster over: shock the magnets from hot to cold, and you could crack them and kill the motor. And then you’re in a real pickle for your next match.

The fans found in old KoPs and in FIRST Choice are pretty excellent and can make a tangible impact on the temps if you leave them on between matches.


#14

We’ve had problems in the past here in NC District over tools in the pits. The RIs tend to be very strict about the “benchtop” definition, which often makes them rule against things like pancake compressors, which they seem to regard as floor-standing tools. I’ve never seen one in use in the pits at NC events. So obviously, our district is a bit strict on this point.

On the good side, though, I can tell you that our mini-bandsaw (with a metal-cutting blade) has made us very popular in the pits on many occasions.


#15

Do everyone a favor and leave the pancake compressors at home. They draw a ton of current, but they are also loud as heck. I’ve gone and asked teams to turn them off because when they are running you can’t have a conversation. We are only inches apart in FRC pits.


#16

I agree they are loud. However, there are many other fabrication/repair processed that generate significant noise volumes. Some of which are at much nastier frequencies. I absolutely agree with trying to keep the noise at a minimum, but you gotta do what you gotta do to fix or (sadly) finish the robot and as long as it is within the guidelines and rules I am not going to get upset with a team that is making noise, as long as it is noise with a purpose.

We typically bring a smaller/quieter compressor and only run it when needed.


#17

Here’s a different though on the topic,

Why do your motors need cooling?

FRC matches are only 2.5 minutes long. Even with back to back matches I’ve never been worried about the temperature of a motor. What you consider “Hot” probably isn’t detrimental to the performance of the motor.

I’ve run CIM drive motors on our practice bot 12 matches straight, with only time for a battery change, while practicing. Yes they get hot. But I’ve yet to notice a significant depreciation in performance.


#18

It depends how close to the edge you are pushing. Last years robot was an elevator design. We knowingly designed/optimized the gearing close to the limit, given that we were using stall to hold the carriage in position. Was not an issue with matches, even back to back elim matches. Motors got warm, really warm, during practice. However, we smoked a CIM at a demo, when we were doing cube piling demos that involved more stall time.

While the sealed (giant heatsink) style motors handle the heat generated by stall much better than the fan cooled motors, you certainly can heat soak them and they recover much slower than the fan cooled ones. Knowing the stall currents and doing the math is important.


#19

I’m not going to call you a liar, but I am going to challenge your ability to perceive performance loss.

It may not kill a CIM-class motor, but it is indisputable that CIMs lose significant power after being run over an extended period, as things expand and friction losses build up into significant heat. How bad and how quickly a motor loses power depends on many variables (gearing, weight, number of motors, CoF, driving style), but 12 matches straight will get any FRC robot on the crappy part of that curve. And losing 1/3 of your power is pretty dang significant.

No fan is going to save you during the match, but getting air on your motors (whether a fan on the can, compressed air through the CIMs’ screw holes, or a vacuum to cool 775s) has been shown to make a difference on how long it takes to bring them down to ambient and regain that power.