Robot having internal heat problem
 

Does anyone know of an easy way to reduce the internal temperature of a small robot - other than heat sinks and fans?

It's a small robot my son assembled and is operated by a small battery... so some of the more sophisticated energy consuming techniques won't work.

Thanking everyone in advance.
Gene

Re: Robot having internal heat problem
 

The two methods you mentioned are the most conventional. Other methods are dry ice and "canned air" turned upside down and sprayed. Be careful with the two of these things though.

Re: Robot having internal heat problem
 

Bigger heatsinks (maybe even a large brick of copper) & more fans, mainly, if you can get a proper air flow going over the hot spots then that'll pretty much fix the problem. If you can't power a fan, I suppose you could try using copper heatpipes to channel heat to a heatsink outside of the robot?
Dry ice might work. It runs out, though. And putting dry ice or turning a duster can upside down and spraying hot spots can create thermal shock, which is generally bad.

Hope this helps.

Thanks for the information - But I should have mentioned
 

the little guy loves to run this thing in the middle of the afternoon - plus the exterior of the can is also used to mount the gearhead motors. The frame, if we can call it that, is a large retangular can from a surplus store.

Since he and his buddies are running this thing for hours in 100 degree + temperatures, short term solutions won't work. Additionally, everything is encased in that oversized ammo can with two exterior vents. So he doesn't really get an "A" for applications in innovative thermal management.

Anyway, I had considered heat pipe and cold plate for the controller and receiver . . . but being only a ME I can't come up with something that will keep the encased electronics cool when the ambient temperature is over 100 F without using a small generator to provided the needed power. Then suddenly his little automated ammo can becomes a big engineering project.

I am honestly stumped.

Re: Thanks for the information - But I should have mentioned
 

Paint it white, the olive drab ammo canister probably absorbs quite a lot of heat from the sun. Additionally, you can channel the heatpipes to the ammo can so that the heat spreads throughout the metal shell (I'm assuming it's metal, since I've never seen a plastic ammo box). 100*F for electronics isn't really bad for electronics, now if it were 100*C...

Re: Robot having internal heat problem
 

why does it need to be enclosed in a can?

Drilling ventilation holes would work wonders.

Re: Robot having internal heat problem
 

I like the drilling holes idea but it takes away from the asthetic value of the the ammo can. You can add fins (painted to match) to the outside of the can so that airflow will cool the exterior, then mount the electronics (the hot bits) on the interior of the can.
Some kind of scoop intake on the bottom would be out of sight and vent holes on the top would allow convection cooling to remove some of the internal heat as well.

Re: Robot having internal heat problem
 

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).

Re: Robot having internal heat problem
 

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

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

Re: Robot having internal heat problem
 

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!!

Re: Robot having internal heat problem
 

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.

Re: Robot having internal heat problem
 

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.

Re: Robot having internal heat problem
 

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.

Re: Robot having internal heat problem
 

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.

Re: Robot having internal heat problem
 

IANAE, but what about a cheap cooling arrangement, such as this, on a smaller scale? If the tube and tank sizes could be sorted out, it would seem like you could get things a bit cooler.

Re: Robot having internal heat problem
 

The M1As use internal air conditioners to keep the temperature below 95 F. because the fire control systems are all electronic. Please don't ask me for more information about the details of these systems.

iRobot also warns military end-users of potential heat related problems associated with desert operation.

Aircraft avionics in addition to the weapon control systems are equipped with some very expensive cooling devices to include tubes, plates AND Peltiers.

Added:
Here is a overview of Peltiers: http://www.dansdata.com/peltprac.htm
The operative phrase is high amps. As he mentions, the efficiency is increased as the load is increased. For the small ammo-bot, I think they may be the kiss-of-death because of battery requirements. But then, I'm only a ME not a EE.

Re: Robot having internal heat problem
 

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... ;-)

Re: Robot having internal heat problem
 

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.

Re: Robot having internal heat problem
 

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

Re: Robot having internal heat problem
 

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?

Re: Robot having internal heat problem
 

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

Re: Robot having internal heat problem
 

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.

Re: Robot having internal heat problem
 

or put ice cubes in a small freezer bag

Thanks for the valuable input guys!!
 

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.

Re: Robot having internal heat problem
 

Anytime, just ask. Good luck! 73's