Compressed air for rapidly cooling motors?
 

I've heard of a few teams using compressed air to cool motors between back to back matches. Is this bad for CIM motors on a drive base? Is there any real performance gain to rapidly cooling motors before a match?

Re: Compressed air for rapidly cooling motors?
 

Compressed air coolant is usually used in-between back to back matches (such as finals) to cool drive train or other high use motors. Electric motors preform better when they are cool, and have a lower risk of burnout. Some companies do make heat-sinks for CIM motors, which you may have seen in the KOP, but they are bulky and not terribly effective.
There is no real risk of damage, and it isn't likely that you will have to do it more than 1 or 2 times during a competition.
Students from other teams have told me that they've been doing it for years without issue.

Re: Compressed air for rapidly cooling motors?
 

It's not the air that is cooling the motors, it's the super cold propellant that is expelled when these cans of air are turned upside-down.

Very hot CIM motors are not happy motors.

Re: Compressed air for rapidly cooling motors?
 

It is interesting to note that (based on a number of posts on CD, not my own experience) that the damaging and performance robbing heat of a CIM is located on the rotor, not the stator or outer case.

The rest is my reasoning, not something proven through experience:

The rotor is only in significant thermal contact with the outer case at the bearings and somewhat less at the brushes; in each case the area of contact is limited or rapidly moving or both. There are also radiation and convection acting within the motor case.

Therefore, the most effective place to cool a CIM may prove to be conduction through the CIM output drive shaft. If your gearbox design allows it, you may wish to try cooling your CIMs by spraying their output shafts and pinions.

I am not familiar with anyone specifically trying to draw heat out through the drive shaft, but it should not be to difficult to design a heat sink that functions as its own fan and which could be attached to a CIM or mini-CIM when they are used in offset gearboxes.

Re: Compressed air for rapidly cooling motors?
 

You have less of a chance damaging the motors in this case with a quick cooling off than still running them when they are hot. The CIMs and others lack their own cooling ability like TEFC (totally enclosed fan cooled) and others that have higher duty cycles. We aren't normally using the motors for what they are designed to do in normal operation so some choices have to be made.

Re: Compressed air for rapidly cooling motors?
 

DO NOT use a canned "air" duster to cool it, especially the liquid. Spraying highly flammable liquid that gives off highly flammable fumes onto a burning hot motor near electrical stuff will not end well! Not to mention that the fumes are also highly toxic. ::ouch:: Regular compressed air, as in what you get out of a compressor that's used for riveting/nailing/etc, will cool the motors. If the pressure is high enough, it will be cold enough to cause frostbite. Even if it's not cold, passing the cool air over the CIMs will cool them down. It's like a fan blowing on a heat sink.

Re: Compressed air for rapidly cooling motors?
 

If you want to cool down your robot and aren't too chuffed about safety, here's a quick way.:yikes: ::ouch:: :ahh: :rolleyes: ::safety::

Re: Compressed air for rapidly cooling motors?
 

Game Announcer: "Team xxxx just got a red card for using unsafe liquids and shattering a robot..."

Wait a minute...I just got an idea...anyone have a spare boulder?

Would be kind of interesting to see what would happen to a boulder going through a shooter after being super frozen like that

Re: Compressed air for rapidly cooling motors?
 

In normal canned air there is no flammable liquid. The cooling effect is simply from the rapid decompression of the highly pressurized air.
The "fumes" are just air.... when you see frost on the item that is being cooled it is a result of the cold object's reaction with the humid room air. You might also see condensed water from the air in a humid environment.

Sometimes manufacturers add something called a bitterant to the air to deter individuals from inhalant abuse. The can will tell you if it contains this material but it is not hazardous and is definitely not flammable. A common bitterant is denatonium... the name is a reference to the denaturing quality of the substance... denaturing is adding something so it cannot be consumed by humans. You can avoid this in canned air if you purchase canned air without a bitterant.

I am concerned that you are spraying something other than "canned air" which is normally used as a duster. Many things are in spray cans.... and you would not want to spray WD40 or some other petroleum based material for this use but canned air would be fine.

You want the rapid decompression to happen as it hits the motor, this super cooled air will cool the motor. Normal compressed air can work... but the cans are usually a much higher pressure and will cool more and you cannot have a compressor in your pit anyway other than the one on your robot or the one you use in conjunction with your robot to fill your pneumatic tanks.

Re: Compressed air for rapidly cooling motors?
 

Please provide a link where this "normal canned air" that contains only (or even mostly) pressurized air (N2 & O2) can be purchased.

Re: Compressed air for rapidly cooling motors?
 

Not exactly. Air is mostly nitrogen and oxygen with some other gases, while the contents of a can of "Dust Off" is not, instead being a mix of non-flammable gases (with virtually no oxygen or nitrogen).

The permanent magnets surrounding the CIM motor, and in contact with the case, are a ceramic material which, like some glass materials, can shatter when exposed to a very rapid temperature change. So just dropping a hot CIM into liquid nitrogen will case irrepearble damage to the CIM.

That being said, it isn't all that fragile and most cooling methods available to an FRC team are fine - just take it a little easy, OK?::safety::

Re: Compressed air for rapidly cooling motors?
 

https://en.m.wikipedia.org/wiki/Gas_duster

Note that it says they're filled with fluorocarbons. Quote from the "Safety" section of the article:

Though not extremely flammable in gaseous form, many dusters use a fluorocarbon that can burn under some conditions. As such, there is also a warning label present on some gas dusters. When inverted to spray liquid, the boiling fluorocarbon aerosol is easily ignitable, producing a very large blast of flame and extremely toxic byproducts such as hydrogen fluoride and carbonyl fluoride as a combustion product.

And what caused this if it's not flammable? Yes, a commenter said it was the CPU, but that computer was unplugged.

Re: Compressed air for rapidly cooling motors?
 

I stand corrected. At our facility we are using a refillable air duster which does not contain anything but the compressed air I put in.

We also have a couple of these:
http://www.amazon.com/Best-Canned-Co...B03 7HQZK9F4W

As an aside, nothing burns in a liquid form.... it has to become a gas. Of course the concentration of the gas vapor above a liquid amount may be higher than normal fluorocarbon and if it is truly in a boiling state gas is present.

Re: Compressed air for rapidly cooling motors?
 

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.

It had been suggested that we use the same method, since we also had thermal problems with the CIM heat in 2014 in the elims (especially finals) matches of Galileo, but we ended up fanning them with a sheet of polycarbonate since it was a common belief (on 1318) that super cooling CIMs was bad for them. I'm expecting to have more thermal issues this year, even at the PNW District Championship next weekend.

Re: Compressed air for rapidly cooling motors?
 

Motors or breakers?

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

Re: Compressed air for rapidly cooling motors?
 

Motors.

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

Re: Compressed air for rapidly cooling motors?
 

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.

Re: Compressed air for rapidly cooling motors?
 

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.

Re: Compressed air for rapidly cooling motors?
 

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.

Re: Compressed air for rapidly cooling motors?
 

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.

Re: Compressed air for rapidly cooling motors?
 

This should help answer your question.

Re: Compressed air for rapidly cooling motors?
 

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.

Re: Compressed air for rapidly cooling motors?
 

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

Re: Compressed air for rapidly cooling motors?
 

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.

Re: Compressed air for rapidly cooling motors?
 

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!

Re: Compressed air for rapidly cooling motors?
 

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

Re: Compressed air for rapidly cooling motors?
 

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

Re: Compressed air for rapidly cooling motors?
 

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.

Re: Compressed air for rapidly cooling motors?
 

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

Re: Compressed air for rapidly cooling motors?
 

If you mean replacing the bolts holding the motor together with different ones... I would think this is a violation of R30:

Those bolts are pretty integral to the mechanical system of the robot... without them the whole thing falls apart and stops working!

Re: Compressed air for rapidly cooling motors?
 

Nope, a CIM motor has two openings in it that are entirely legal to blow air into without modifications.

-Aren

Re: Compressed air for rapidly cooling motors?
 

Very cool, Aren! 91979A605 or something similar?

Re: Compressed air for rapidly cooling motors?
 

Yup, you can even get 10-32 to 1/4" tube push to connect fittings to make it easier to hook up air.

Feel free to come by 1296 at champs, we'll also be running it.

-Aren

Re: Compressed air for rapidly cooling motors?
 

So is the air actually flowing during a match or only being hooked up afterwards between matches?

Re: Compressed air for rapidly cooling motors?
 

Between.

Nothing hooked up to the robots pneumatics system.
It's mainly about air flow, and the robot system isn't the greatest for that anyway.

The testing I did on some of this helped lead to motors.VEX.com
Mainly the "peak power duration test"

-Aren

Re: Compressed air for rapidly cooling motors?
 

We had our pit partners ask for an ice pack during the finals to which we gave them our ice pack from our first aid kit :P I guess that works lol

Re: Compressed air for rapidly cooling motors?
 

Al,

I thought these breakers were thermal (too much heat and a bi-metallic strip trips). What does it mean that there isn't enough thermal mass? Just that the electric heat builds up too quickly for the temperature at the start of the match to matter much?

That doesn't really jive with my (anecdotal) experiences. The only time I've ever tripped a main breaker is after consecutive matches where I assume heat would be building up in the breaker. Is it that that the heat building up in every motor makes everything less efficient resulting in more current draw and more heating? Or something else?

Re: Compressed air for rapidly cooling motors?
 

Ian, There isn't enough metal to hold the cold long enough to be effective. It likely will reach ambient before being placed on the field. The bimetal is the silver part in the picture. It is roughly .020 to .040 thick. The terminals connect to the left and right side of the bimetal. The terminals are connected to the #6 on both sides which will transfer temperatures and draw the parts close to ambient. The handle parts are removed in this drawing. Even spraying directly into the handle opening is unlikely to take this part down below ambient all things considered. The base is Bakelite.

Re: Compressed air for rapidly cooling motors?
 

Al - my understanding was that the practice of cooling of breakers WAS to get them back to ambient, as opposed to potentially starting the match at higher than ambient temperatures and thus biasing the breaker to trip earlier than may be warranted.

Re: Compressed air for rapidly cooling motors?
 

As someone that focuses on safety, I don't recommend using an ice pack from a first aid kit to cool a motor on a robot unless you have plenty of ice packs in your kit to spare. An actual person may need that ice pack due to an injury. Just a friendly observation... ::safety::

Re: Compressed air for rapidly cooling motors?
 

Evan, there is enough heat sink in the wiring and mounting that I would bet the breaker is back to ambient in a minute or two.

Re: Compressed air for rapidly cooling motors?
 

I have not tested the main breaker yet but I did get an opportunity to test the 30 amp breaker when we were debugging our current control software. We found it was difficult to get 30 amp breakers back down to an ambient temperature in a minute or two. We did get the 30 amp breakers to still open below 30 amps. Bare in mind we got them really hot (painful to touch) and the adjacent wires were warm to touch but it prompted us to cool these if we have back to back matches. However we only bother to do this under those circumstances and only particular circuits.

Not sure about the main breaker because we are careful with managing our current draw but in rapid practice matches we have gotten our battery lead wires quite warm. I hypothesize that this circumstance would limit the cooling of the breaker or at the very least have a temperature elevated than ambient. Maybe we will try to cook the practice robot this summer to see what happens.


Also to correct some misconceptions about using can air. You can buy non-flammable varieties and they come with lovely little set of warnings explaining the operating temperature. Those are the ones I buy, you can get them on mcmaster even. You even buy varieties designed for rapid cooling so you don't even have to turn the can upside down. The one I have has an operating temperature up to 450 degrees F. Paper burns at 480 F so if your robot is over 450F in any area, you probably should be using a fire extinguisher instead.

For the propellant HFC-134a, its non-flammable.
https://www.chemours.com/Refrigerant...c134a_push.pdf
It should be noted its non-flammable in air in temperatures up to 212F in normal atmosphere conditions. It can be ignited in the presence of oxygen or chlorine.

Re: Compressed air for rapidly cooling *circuit breakers*
 

Quote:

Originally Posted by Ian Curtis (Post 1570941) I thought these breakers were thermal (too much heat and a bi-metallic strip trips). What does it mean that there isn't enough thermal mass? Just that the electric heat builds up too quickly for the temperature at the start of the match to matter much?

One way to find out:
MATH!
(Hold on to your hats, people; this is gonna be a bumpy ride.)


The internal temperature required to trip these breakers is quite high relative to their size: a bit over 300 degrees Fahrenheit (149 C, or 422 K), to be precise (citation). At an ambient temperature of 77 F (25 C, or 298 K), they are still guaranteed to permit at least 120 A of continuous current for an indefinite period of time without tripping; that means that the steady-state internal temperature will never exceed ~270 F under those circumstances.

Given this, we can find that for a 120 A load, the approximate steady-state temperature rise between the ambient air and the breaker snap element is...

delta T = (270 F - 77 F)
delta T = 193 degrees Fahrenheit (or 89.4 C)

From thermodynamics, we also know that the rate of heat dissipation through a solid object is directly proportional to the temperature difference between two points (in this case, one point is inside the breaker switch and the other is in the air directly next to the surface of the breaker). From this, we can find a good approximation for the rate that the breaker in question can dissipate heat energy into the surrounding air.


* For the sake of my own sanity, I’ll use SI units for the rest of the math: degrees Kelvin for temperature, Joules for energy, et cetera. *


Looking around, I can't seem to find a stat for the main breaker's electrical resistance. In the absence of a known value, I'll just roll with 0.05 ohms as a fairly reasonable guess. This gives us a thermal conductance of...

C = (power dissipated) / (temperature rise)
C = (I^2 * R) / (dT)
C = ((120 A)^2 * (.05 ohms)) / (89.4 C)
C = 8 Watts per degree Celsius

...Which means that each additional degree of difference between internal and ambient temperature will increase the rate of heat energy transmission by 8 Watts.


Next, we can find a full equation for temperature (big T) as a function of time (little t), given the following constants: current (I), resistance (R), thermal conductance (big C), and initial temperature (Ti). We will also need the main breaker's specific heat capacity (little c), which will be a constant representing how much energy (in Joules) is required to raise the breaker's temperature by 1 degree Celsius. Here's how we work that out:

Temperature = (specific heat capacity) * (total heat energy)
T = c * E

Now to find the change in temperature over time, we take the derivative:

(rate of change in temperature) = c * (rate of change in heat energy)
dT/dt = c * dE/dt

Expand:

dT/dt = c * ((power usage) – (C * (T - Tambient))
dT/dt = c * (I^2 R – CT + CTambient)
dT/dt = c * (I^2 R – CT + CTambient)

Integrating this over the time range (0-t) lets us find the final temperature with respect to time:

T(t)= c*∫(0-->t)〖(I^2 R–CT+CTambient)dt〗

Well, this is fun. Looks like we've got ourselves a full-blown differential equation, which means that our dependent variable can't be extracted completely from the independent variable. To avoid the tedium of university-level DiffEq, then, we'll use a computer to help us from here on out.

T(t)=(I^2 R)/C+k1 e^(-Cct)+Tambient

Here, k1 is a constant of integration; that means that we need to solve for that value before we can proceed any further. If we set t = 0, that should help:

T(0) = (I^2 R)/C+k1 e^(-Cc(0))+Tambient
Ti = (I^2 R)/C+k1 e^0+Tambient
Ti = (I^2 R)/C+k1 (1)+Tambient
Ti = (I^2 R)/C+k1+Tambient

Solving for k1, we get:
k1 = Ti-(I^2 R)/C-Tambient

That’s pretty ugly, but we’ll plug it back into the big equation anyways:

T(t)=(I^2 R)/C+(Ti-(I^2 R)/C-Tambient ) e^(-Cct)+Tambient
T(t)=(I^2 (.05))/8+(Ti-(I^2 (.05))/8-Tambient ) e^(-8ct)+Tambient
T(t)=I^2/160+(Ti-I^2/160-Tambient ) e^(-8ct)+Tambient

Next step: solve for the specific heat constant (c)!
Consulting the main breaker's data sheet again, we find that 5 seconds is the time it takes for the breaker to trip if you start from room temperature (defined as 25 C) and run about 3.66 times the rated current. Our battery can't actually deliver this kind of current, but that doesn't matter just yet. These numbers still give us a useful data point (Ti = Tambient= 298 K, I = 439 A, t = 5 s, Tfinal = 422 K, ), which is precisely the sort of information we need to find (c)! Feeding this into our equation, we get:

T(t)=I^2/160+(Ti-I^2/160-T_ambient ) e^(-8ct)+Tambient
422=〖439〗^2/160+(298-〖439〗^2/160-298) e^(-8c5)+298
c = 1/40 (-3 log(3)-log(19)-log(337)+2 log(439))
c = 0.002716 degC / Joule

Plugging that result back in, we get our final equation for the breaker's internal temperature with respect to time, given the starting conditions (Ti), (Tambient), and (I):

T(t)=I^2/160+(Ti-I^2/160-Tambient ) e^(-8(0.002716)t)+Tambient
T(t)=I^2/160+(Ti-I^2/160-Tambient ) e^(-0.02173t)+Tambient

Now we consider the case of a 6-CIM drivetrain, running on 40 A snap-action breakers. If you manage to stall out all 6 motors, you'll approach the battery's maximum discharge current of 270 A (citation) for a few brief, glorious moments before something gives out. Let's leave aside the guaranteed RoboRIO brownout condition after only a couple seconds of this (citation), and also ignore the fact that the battery can only handle that kind of current draw for up to 5 seconds before it starts to sustain permanent damage. We'll even neglect the fact that (depending on manufacturing tolerances) the snap-action breakers might start to cut you off as soon as 4 seconds into the stall (citation); all this, so that we can focus on the main breaker by itself.
Subjected to 270 amps' worth of abuse, the main breaker is rated to hold out for anywhere from 6-25 seconds (there’s your manufacturing tolerance again) if you start from room temperature. For a quick sanity check, let’s throw this data point into our new equation and make sure it jives:

Tfinal = 300 F = 422 K
Ti = Tambient = 77 F = 298 K
I = 270 A
422=〖270〗^2/160+(298-〖270〗^2/160-298) e^(-0.02173t)+298
0.7278=e^(-0.02173t)
t = 14.6 seconds before the breaker trips

Cha-CHING! This number is squarely in the middle of the range where we expected to find it.


With that success in hand, we can find out exactly how long it takes for the inside of the breaker to cool down after a hard match. Just plug in the following values:

Ti = 270 F = 405 K
Tambient = 77 F = 298 K
I = 0 A (robot is off)

…And since we know that temperature changes are asymptotic (the final value is never quite equal to ambient; it just gets really, really close), we’ll ask for a Tfinal of 80 F = 300 K. Plug that all in, and solve for t:

300=0^2/160+(405-0^2/160-298) e^(-0.02173t)+298
2=107e^(-0.02173t)
t=183 seconds

All it takes is 2.5 minutes after a hard match, and the innermost parts of the main breaker are already back down to room temperature.


Now let’s investigate what happens if you chill the main breaker down to, say, -60 degrees Fahrenheit (source) by spraying it with a can of gas duster propellant. Will it still be cold by the time the match starts?

Ti = -60 F = 222 K
Tambient = 77 F = 298 K
I = 0.8 A (idle current)
Tfinal = 74 F = 296 K
296=〖0.8〗^2/160+(222-〖0.8〗^2/160-298) e^(-0.02173t)+298
-2=-76e^(-0.02173t)
t=167 seconds

Once again, it only takes a couple of minutes for the innermost parts of the main breaker to get back up to room temperature.

Okay, so we know that the extra chill doesn’t last all that long, but I’m still not quite convinced that there isn’t any benefit to be had. 167 seconds is still longer than a match, after all! What happens if we chill the main breaker at the last second before loading the bot onto the field, then start the match by immediately ramming an opponent and stall out our 6-CIM drivetrain? That’s the real situation where we might want the extra chill, after all. Exactly how much longer can we keep drawing the max current before the main breaker trips?
Part 1: load the bot onto the field

Ti = -60 F = 222 K
Tambient = 77 F = 298 K
t = 20 seconds
I = 0.0 A (robot is off)
Tfinal =0^2/160+(222-0^2/160-298) e^(-0.02173(20))+298
Tfinal =248.8 K=-11.8 F

Part 2: wait for match to start

Ti = 248.8 K
Tambient = 77 F = 298 K
t = 40 seconds
I = 0.8 A (idle current)
Tfinal =〖0.8〗^2/160+(248.8-〖0.8〗^2/160-298) e^(-0.02173(40))+298
Tfinal =277.4 K=39.7 F

Part 3: stall the drivetrain

Ti = 277.4 K
Tambient = 77 F = 298 K
Tfinal = 300 F = 422 K
I = 270 A (max possible current from battery)
422 =〖270〗^2/160+(277.4-〖270〗^2/160-298) e^(-0.02173t)+298
t=16.7 seconds

Our previous max stall time was 14.6 seconds, so the most benefit that we can possibly expect to get from chilling the main breaker is 2.1 extra seconds of stalling out the drivetrain once the match starts.

So now it seems like this could make the difference between dying in auto and surviving until teleop...but wait! Remember that the RoboRIO would brown out long before that happens, and that you'd probably also start tripping the snap-action breakers before you get to that point as well? That means that it's practically impossible to trip the main breaker before teleop, regardless of whether or not we chill it first...

So, what do you think?
Is it really worth risking the possibility of damage to your robot and/or yourself, or is this just a solution in search of a problem?

Re: Compressed air for rapidly cooling motors?
 

I really thought this topic was going to about pneumatic vortex coolers.

Re: Compressed air for rapidly cooling *circuit breakers*?
 

My mind is blown. :ahh:

I'm just worried about an ice-pack in a first aid kit. ::safety::

Re: Compressed air for rapidly cooling motors?
 

I just found out about those a couple years ago. So cool.

Re: Compressed air for rapidly cooling motors?
 

And we've got one, tis quite nifty.

-Aren

Re: Compressed air for rapidly cooling motors?
 

A few years ago, our team used a high output squirrel cage fan to cool the robot between matches, especially in the finals,,we not sure if it helped but there wasn't a problem. Where we know it did help was with the circuit breakers as the drive team knew that the cooler breakers eliminated lag. It also helped that we replaced all of the drive train breakers going into the finals. We were runner up finalists, so it didn't hurt.,, It's the little things that break you, stay after them.

Re: Compressed air for rapidly cooling motors?
 

Could you please explain what lag you are referring to?

Re: Compressed air for rapidly cooling motors?
 

They said they could notice the breakers tripping when they pushed someone, or similar, after they changed the snap action breakers, it was less noticeable. Consistently tripping breakers or running at close to their limit will weaken the bi metal strip.. allowing them to trip at less than the rated load.

Re: Compressed air for rapidly cooling motors?
 

Ryan,
Thanks for the exercise. The main breaker resistance is actually much less than your guess by a factor of 100 though. A new breaker that has never tripped (resulting in some pitting of the contacts) will have a series resistance in the .0005 range (verified at Motorola labs a few years back). The battery is capable of 600 amps at full charge albeit at reduced terminal voltage due to the internal resistance of the battery. I was unclear if you included heat dissipation in the wiring connected to the breaker. I believe that is a sufficient source of heat loss as it increases the surface area exposed to ambient air making the return to ambient for the breaker even less than calculated. It is great to know my hunches are backed up with math. Cool!

Re: Compressed air for rapidly cooling motors?
 

Excellent, I knew that someone on here would have an actual number for this! I'll probably update my math sometime later when I get a chance.

As for dissipation through the wires, my numbers are based on published data from the manufacturer. I expect that it is safe to assume that the manufacturer's test rig included appropriate-gauge wires, and therefore that their data therefore includes heat dissipation through said wires, but it would indeed be preferable to know more about how they gathered that data. ::rtm::

The ideal thing would be to gather some data firsthand using a test rig that is specifically designed to replicate the conditions found on an FRC robot (match the wire gauge, crimp and terminal styles, wire length, and air circulation)... For now, however, I'm content in the knowledge that my current level of precision is good enough to get a working idea of what's actually going on inside the breaker.

Re: Compressed air for rapidly cooling motors?
 

Just another hunch, but I would guess they might use some really big wire to reduce the resistive losses at high current. I have not broken the breaker base to see what the size of the conductors is between terminals and internals.