It's been my intention to make an amphibious quadcopter for a long time. Unfortunately, I'm lazy so what follows are my waterproofing tricks.
As mentioned, BLDCs are essentially waterproof already, with the bearings being surprisingly resistant to corrosion. The magnets and stator aren't so much. If you want them to last the BLDC outrunner motors need to be disassembled at which point you can coat the stator & magnets in MG Chemicals aerosol silicone conformal coat or dip it in epoxy based paint with the bearings removed. The cooling of the motor windings will obviously be compromised so you can use thermally conductive epoxy or simply swing smaller props and reduce your current draw. You can skip waterproofing the motors entirely if you dunk them in 99% alcohol after each use and that will protect the bearings as well. This will shorten their life considerably, but I don't spend more than $12 on BLDCs so I don't really care if I have to replace them every couple months.
Put all of your control electronics in a cheap tupperware container and backfill it with paraffin wax or silicone rubber. This can include your ESCs, although I've had reasonable success potting those in automotive grade Silicone RTV. This is controversial because the acetic acid supposedly will corrode the pcb and components over time, although I've never had any problem.
I just put my LiPoly batteries in a latex balloon and seal the mouth against the wire connector using hot glue.
I've run all of these components completely submerged in a bathtub using the above techniques.
There was an ROV article on the front page awhile ago:
The amount of CoTs things I've seen work underwater with the stupid tricks listed above is surprising. If you have to have moving parts, make them non-corrosive, and use epoxy to pot components that need a heatsink. Silicone, hot glue, wax, mineral oil, and rubber diaphragms for everything else. I've never used these techniques deeper than 40 ft, but my default position these days is "it'll work underwater" until I've seen these fail.
Conforming solutions is the way to go. I believe they work for ESCs but there other gooey black stuff one can buy from automative stores and dip the ESCs into this runny goo that dries up waterproof.
A fellow waterproofer :)
I've looked in to "PlastiDip" and have used it to some success on electical wiring. I'm a little bit convervative on what I apply that type of coating to because the solvents it contains are pretty aggressive, but I expect it would work for many things as well. The IEEE Spectrum article includes using vinyl tubing to waterproof wire insulation which I have heard many people having problems with. At higher pressures, water seems as difficult to keep out of where it doesn't belong as liquid helium :P
I'll have to explore the conformal coat you linked to as the RTV seems to invite the cautionary warnings from every electical engineer I mention it to.
Mineral oil is a common one because it's affordable and common however I've been frustrated by it's tendency to eat latex which is why I favor paraffin wax for many applications. When melted to a liquid, I alloy the wax with mineral oil based on the recommendation of a candle maker I once spoke to. This solves the brittleness fairly well although the melting temperature makes it unsuitable for some higher temperature components like power transistors.
A cheap available source of silicone oil I have found is "AstroGlide X" which is more compatible with the latex rubbers I like to use. I imagine industrial silicone oil is cheaper per unit volume, but the minimum order quantity can be larger than I want to use for many applications. Obviously the dielectric stength is insanely high as is true of paraffin wax & oil. I've considered de-ionized water for acoustic applications to minimize the speed of sound interference issue, although I have no reason to believe that silicone oil would present a significant problem that couldn't be calibrated around.
Hello to you too Gerry
Such joy to waterproof Arducopter ;)
The solution I mentioned in the earlier post was the more reasonably priced one, I found databases of these chemicals some sold at about $1000/litre!!!
If the water is salt free, I think the problem is solved, given the copter is using brushless motors. Some sort of conforming spray + the mineral oil mix you had mentioned. "AstroGlide X" is great for the ESCs.
Even at that, you need to process the copter post-flight. After landing you need to fan it out to try it and let the brushless motors run for few minutes to clear the water.
I believe the problem persists for salt-water flights. I have not heard any breakthru in protecting circuitries over the salty waters. All sorts of jells are proposed, but nothing I found suitable for copters. Probably more digging is required on my part
Consider waiting till mid 2012 for this product to be available. http://neverwet.com/
Is is safe to apply a Silicon Conforming Coating to an APM2.5 board? For example, this one:
Would this interfere with any of the sensors or cause any of the chips to overheat under normal use?
If not, anybody got any advice for applying a the coating to the board?
@Oliver, it will interfere with sensors. For example Barometric sensor would die immediately if you add coating on it. So it's not a good idea to coat it. How would coating affect gyros, As that coating is designed for PCBs it would not create any shortcircuits so for other components it would be rather safe to use. Does it make components to warm up, maybe a bit.
So as far as I can see Baro is only problem for you.
@Hai, if water goes in brushless motors it does not short them as there are no open connections anywhere. That's why they are called as brushless. Only thing that you can harm is your bearings especially if flying on Sea areas and you get salt water in motors. Quick rinsing with fresh water usually fixes this ok.
These look pretty waterproof, and they market them as being 'rain resistant':
Pretty clever design, it's mostly encased, with little disc covers over the motors.