Robot having internal heat problem

[KenWittlief]

Originally Posted by Al Skierkiewicz

I like the drilling holes idea but it takes away from the asthetic value of the the ammo can. ...

OK then, bullet holes would work too :^)

BTW, what is it thats producing the heat? the motors or the electronics?

most small hobbie motors have built in blowers. If they dont get fresh air for cooling it defeats the purpose.

If its the electronics, are you sure you really have a problem? If it runs for 2 hours its pretty much heat-soaked to steady state. If its still running at that temp it might be ok.

Most electronics will operate at 95°C without failing (too hot to touch).

[billbo911]

Originally Posted by Al Skierkiewicz

I like the drilling holes idea but it takes away from the asthetic value of the the ammo can.

Originally Posted by KenWittlief

OK then, bullet holes would work too :^)

Why not combine your ideas? An Ammo can riddled with bullet holes seems to fit the theme. You get "aesthetics" and function.
If you are not the shooting type, but still would like it done, look me up. I'm sure we could arrange something.

All "funnin'" aside, can you post a picture of your son's project, it might help us help you find a solution.

[Gene]

Originally Posted by KenWittlief

OK then, bullet holes would work too :^)

BTW, what is it thats producing the heat? the motors or the electronics?

most small hobbie motors have built in blowers. If they dont get fresh air for cooling it defeats the purpose.

If its the electronics, are you sure you really have a problem? If it runs for 2 hours its pretty much heat-soaked to steady state. If its still running at that temp it might be ok.

Most electronics will operate at 95°C without failing (too hot to touch).

Good question Ken. The motors venting heat into the container; the radiant energy coming off the “desert” floor (which can go up to 120 F.) and the direct sunlight. Remember, this is the place where you can’t go barefooted in the summer because you’ll burn the bottom of your feet (second degree burns!!). Moral of the story - If you live in the southwest – live near the ocean or in the mountains.

Anyway, if he insulates his ammo-bot, he protects it from the direct sunlight. If he draws in outside air, he pulls in the hot air radiating off the ground. If he insulates the entire unit, he protects it from the radiant energy – but bringing in outside air is a no-no because the outside air is merely heats the electronics.

He also asked how they’re keep the electronics cool in Iraq. Needless to say, he didn’t like the answer. But I assured him, I had found a great web-site used by some of the brightest minds in the world and since I was at a loss (short of redesigning the ammo-bot) . . . . the forum is his last and only hope.

You see how much faith I have in you guys!!

[sanddrag]

I don't know what size your motors are but if they are standard hobby RC car size you could try something like this with a small electric pump and tank. Do you have a picture of this robot?

EDIT: Actually, isn't there a way to make a fluid flow through a small cooling system just by using the heat (no pump required)? I think I've heard of that before, but I don't remember the details.

[lukevanoort]

Originally Posted by sanddrag

I don't know what size your motors are but if they are standard hobby RC car size you could try something like this with a small electric pump and tank. Do you have a picture of this robot?

EDIT: Actually, isn't there a way to make a fluid flow through a small cooling system just by using the heat (no pump required)? I think I've heard of that before, but I don't remember the details.

Unfortunately, that'll only get it down to ambient temperature unless you use an active cooling method. For that, you need some sort of refrigeration, most units are much too heavy/power hungry, the only thing that I can think of that could do it is a Peltier junction. These are nifty little ceramic (I think) blocks that get hot on one side, cold on the other when you run current through them. Then you have to worry about condensation. Peltiers could instead be used with fans to help reduce the temperature below ambient. I don't know where you could get one though, but they used to be popular with the extreme case-mod/water-cooling crowd so there probably is a place to acquire them. Most will probably be in the 12VDC area, but power consumption is pretty low, (if I remember correctly) 10 NiCd AAAs could probably power it and the robot, NiMHs would be even better. (less toxic) The Robot Marketplace has customizable battery packs you could use.

[Andrew Blair]

Originally Posted by lukevanoort

Unfortunately, that'll only get it down to ambient temperature unless you use an active cooling method. For that, you need some sort of refrigeration, most units are much too heavy/power hungry, the only thing that I can think of that could do it is a Peltier junction. These are nifty little ceramic (I think) blocks that get hot on one side, cold on the other when you run current through them. Then you have to worry about condensation. Peltiers could instead be used with fans to help reduce the temperature below ambient. I don't know where you could get one though, but they used to be popular with the extreme case-mod/water-cooling crowd so there probably is a place to acquire them. Most will probably be in the 12VDC area, but power consumption is pretty low, (if I remember correctly) 10 NiCd AAAs could probably power it and the robot, NiMHs would be even better. (less toxic) The Robot Marketplace has customizable battery packs you could use.

Ooohh...Peltier's...those are cool. I might just suggest this little baby- http://www.electronickits.com/kit/co...tier/ck500.htm

You seem very intent on cooling the air, not just introducing it, so this in a sealed metal box would work quite nicely. Otherwise, just use a plain fan and some bullet holes as Bilbo said.

But I have a question: What kind of kid goes outside in 100 degree temperatures to play with a robot instead of slugging around inside watching TV? Sounds more like some crazed ME to me... ;-)

[Gene]

Originally Posted by Andrew Blair

Ooohh...Peltier's...those are cool. I might just suggest this little baby- http://www.electronickits.com/kit/co...tier/ck500.htm

But I have a question: What kind of kid goes outside in 100 degree temperatures to play with a robot instead of slugging around inside watching TV? Sounds more like some crazed ME to me... ;-)

Outside air would be nice - if it was cooler.

I'm guilty. He and his friends were talking about science projects, the news on TV (Iraq) and neat stuff like iRobot's little devices. So I thought a little robot would be a wonderful learning experience. . . and - well . . . . . it has been.

He rarely watches TV.

[lukevanoort]

Y'know, speaking of spending time inside, couldn't he drive the robot inside?

[Kevin Sevcik]

First, I thought MEs were all about heat transfer. I know I had to learn entirely too much about it in college.

At any rate, I'll add to the chorus. I really think ambient air is your best bet, since anything else requires expending relatively large amounts of (electrical) work in order to cool below ambient. Simple thermodynamics and all that.

Thinking about it, you could just make a rechargable cooling unit, however. Just something you put a piece of dry ice in and it provides enough cooling to last for a few hours. If we could get an estimate on how much current the whole ammo-bot draws we can figure out how much dry ice you'd need. In fact, an estimate of the power draw would be useful for figuring out any cooling solution.

So... basically, what size batteries are we talking about, and how quickly do they get drained?

[KenWittlief]

whats wrong with wet ice? (besides being free from the ice cube maker? :^)

[Kevin Sevcik]

Originally Posted by KenWittlief

whats wrong with wet ice? (besides being free from the ice cube maker? :^)

You'd have to work up som system to get the cold to the electronics and pipe the wet water somewhere away from them. Though I did consider it. I was first thinking of some liquid you could evaporate, Which neatly solves the condensation problem you're likely to have with either wet or dry ice.

[KenWittlief]

or put ice cubes in a small freezer bag

[Gene]

I’d like to thank:

Al Skierkiewicz
Andrew Blair
billbo911
Billfred
KenWittlief
Kevin Sevcik
lukevanoort
NoodleKnight
sanddrag

for all the help, thoughts and concerns provided by a great bunch of guys.

I let the “little fellow” review the thread, then we had a Q and A.

One of the more pronounced issues you guys helped him learn and perhaps one of life’s most important lessons, is that everything has trade-offs. And just as important . . . design and build for an application.

His solution, redesign. Use different more nonconductive outer materials, good insulation, incorporate a larger power source, draw external air until it reaches a predetermined temperature, then to use Peltiers with thermocouples to avoid a constant power drain.

But the big deal, at least to me, is the team concept and importance of listening to everyone’s input . . . because moving “in the opposite direction” may be the wisest decision.

[Al Skierkiewicz]

Originally Posted by Gene

Anyway, if he insulates his ammo-bot, he protects it from the direct sunlight. If he draws in outside air, he pulls in the hot air radiating off the ground. If he insulates the entire unit, he protects it from the radiant energy – but bringing in outside air is a no-no because the outside air is merely heats the electronics.

You see how much faith I have in you guys!!

Remember that no matter how hot the surrounding air is, it is still cooler than the dead air inside the box. If you circulate the air through the box it will take the internal temp down to the ambient. Without a cooling system, that is as good as you can get.

[KenWittlief]

Im not aware of any special cooling being used on electronics in the desert in Iraq.

Motors can get very hot with no problems. Most commercial electronic devices are rated up to 95C (not F, C).

The fact that its 100F in Arizona is no big deal. How hot do you think it gets under the hood of your car in the summer? How about inside your car after its sat in the sun all day? CD player still works just fine pumping out 500W inside a car that is hot enough to kill a dog.

Ambient air should be all you need, even in the desert - you just need to open the case a little and let the outside air in.