Compressed air for rapidly cooling motors?

[Road Rash]

Originally Posted by Ryan_Todd

[SNIP]

My mind is blown.

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

[IKE]

Originally Posted by techhelpbb

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

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

[Aren_Hill]

Originally Posted by techhelpbb

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

And we've got one, tis quite nifty.

-Aren

[Ken Best]

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.

[Ether]

Originally Posted by Ken Best

the drive team knew that the cooler breakers eliminated lag

Could you please explain what lag you are referring to?

[Ken Best]

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.

[Al Skierkiewicz]

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!

[Ryan_Todd]

Originally Posted by Al Skierkiewicz

--snip--

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.

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.

[Al Skierkiewicz]

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.