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I am building a robot that is going to have to withstand things such as heat and water
and I need a way to wetherproof a metal box that will hold all of my electronics. Would rubber seals work?
How much heat and how does it reach the box (radiated, flames, what)?
How much water and how does it reach the box (immersion, rain, what - fresh- or saltwater)?
Well my idea is to make my robot impervious to high heat temperatures (fire) and water splashed on it every now and then.
It should be able to go through 2 1/2 in puddles and what not. It should be able be withstand excessive heat (flames) for 90 minutes.
2½" puddles isn't really an issue, but direct flames for 90 minutes may be something of a challenge, as your electronics will behave erratically when it reaches somewhere between 80°C and 120°C (if not sooner), but htere's a huge difference between a welding torch directly against the box (burning through in a short time) and gentle flames nearby.Best would probably be an aluminum box, with aluminum shields mounted 10..20mm out on aluminum rivets/tubes/whatever, to keep some of the heat away from the box itself.A mist of water and a fan mounted in a sensible way may help as well (as long as it doesn't feed the flames.
What kind of wheels are you planning for going into a fire?
Is this for some school competition (or similar), or is it something you are planning for serious use?
This is serious use
Then perhaps it would be viable to make a hollow wall box that could be packed with dry ice - that would both cool and quench flames (but it can be hard o find an instant supply of dry ice).The electronics shouldn't get too cold either, but I don't think that would happen in a burning building.
Assuming it would be for remote monitoring, you should factor in extra time to get a cam to work reliably in the heat - talk to companies that specialize in that. Perhaps they can tell you exactly what optics will work best and whatever else you need to address.
Is it possible to use a large cooling fan to direct the heat away from the electronics just like you said above?
Ok I just contacted the company to see the maximum temperatures the camera can run at. I'll post once I get a reply. I am using a weather proof security camera with a wireless transmitter and receiver so we'll see what they say.
Ok the reason why I am steering away from dry ice is because I don't want to constantly be buying dry ice.
I am more interested in the mist idea right now though. Would it be similar to how a humidifier would work for your home?
Edit: Even though the costs may be a bit more expensive, I think the solution involving dry ice will work best. I'm not sure how much dry ice I will need though.
If I remember correctly doesn't dry ice sublimate 1 pound every 24 hours, but for my case this time will probably be sped up.
Would a reusable pack like this work? http://www.cameronpackaging.com/Dry_Gel_Ice_Sheets.html#cold
There is really good info on this site about waterproofing servos:
I like the box within a box idea, but in that case I don't know why you would want to have an outer box of aluminum, which conducts heat well. Why not waterproof an internal metal box and then have the outer box be something that is more insulating, like lexan or carbon fiber. Lexan can melt, but it takes an awful lot of heat to do that. It is light, easy to work with, and insulating.
Q - What is the maximum temperature at which standard motors can be operated?A - The life of the electrical insulation and of the lubricants are adversely affected by high temperatures. A generally accepted "rule of thumb" is that for every 10°C increase in operating temperature, life is halved. NEMA standards normally limit the maximum ambient temperature to 40°C. A probable life of approximately five years under normal operating conditions 8 hours/day, 5 days/week, (ambient temperature below 40°C, and uniform rated load) can usually be expected. Due to the many variables, life can only be estimated before testing under actual operating conditions.
Lexan (polycarbonate) will melt and curl up in a fire. The max. permitted temperature, although high for a plastic, is "only" ~250° (that's why it's so easy to heat bend with a hot air gun) and a fire can reach pretty high temps. If subjected to dry ice,it will be brittle and crack if knocked or vibrated.Carbon fiber, if heated to a point, looses the resin that holds the fibers together and the fibers without the resin can hold nothing.I tried to heat bend a carbon fiber rod once... Emphasize on once.It has to be a mostly all metal construction, perhaps with some ceramics thrown in for street cred (and to get rid of any excess money )
Outer materials have to be able to withstand up to 90 minutes in a fire (which may mean more than 1000°C).Inside the box, temperatures should be kept under 100°C, preferably much lower (like 50° max).Motors and wires should be kept low as well, isolation on wires could be Kynar or something similar to help withstand high temperatures, but the magnets in the motors will demagnetize if they get to somewhere between 100°C and 180°C (depending on magnet material) special high temp motors can go to above 400°C, but here's what one manufacturer says on the subject (my emphasis)
The more I think about it, the firmer my beliefs in dry ice gets.Designing something that keeps its joy in a fire does take careful selection of materials, wicked cooling techniques and a head full of hair (for regular pulling) - all in all a worthy challenge
...have you thought of using a small fire-proof safe...