how to waterproof hardware?

Forum 2005-2010 (read only) Hardware Interfacing
1

I want to put an ardunio, nordic wireless board, accelerometer, compass together with motor controllers and motors on a model sail boat to be the control package.

I bought about 20 motors on ebay - great deal £2 each with shipping and they have a position encoder each as well :).

So in my fuuzzy bottom up, top down and inside out way I am working slowly to get it sailing. This weekend I planing to test the sail winches on a sail rigged to a board.

I am not confident that my thoughts about how to keep things dry are good... and I would love to hear your thoughts.

Current idea: cut soda bottle in half and mount the electronics inside; run any wires needed out through a hole drilled in the cap filled with a sealant from the hardware store.

Shrink one end of the bottle with heat then force them together with vasoline for a better seal and tape up with lots of electrical tape.

Benefits: cheap, light, and hopefully will float when the boat comes unstuck :).

However, I am struggling with the motors that I need to trim the sails, rudder etc. Almost about to just mount them on top of a piece of light ply and hope it never tips over...

suggestions requested :slight_smile:

Regards,
Dave

2

I am facing this same issue as well. I am going to be mounting all of my hardware inside a boat. While there is a lid, I don't trust that it will stay upright 100% of the time. For testing, I was thinking of wrapping the board components in a few layers of plastic ziplock bags. I know its not completely waterproof but should hold a bit if the boat capsizes.

I don't have any ideas for the other parts. Looking forward to any suggestions as well.

3

I have not done any underwater stuff, but I had a plan to make an underwater infrared light sensor with camera once... I was going to use a plastic Ferrero Rocher box and seal it with heat glue. The thing is the plastic is brittle and the heat glue doesn't always seal properly.

I wouldn't use electrical tape neither. Maybe a good tube of silicone sealant (like for the bathroom) would make it perfect. If it's good enough to hold fish tanks together, then the arduino should be safe, just be sure that the seal is done right. You could even have the wires coming through the silicone.

Hope some of that might be useful to you.

4

Almost about to just mount them on top of a piece of light ply and hope it never tips over...

Suppliers have a name for people like that: they're called "repeat customers" :wink:

There are lots of people building RC boats, so there must be multiple suppliers of water-resistant servos and motors out there.

For protecting electronics, I'd look at food and medicine containers like Tupperware and its competitors. Lots of shapes and sizes, with good seals you can open and re-close. You might also be able to use them to enclose standard servos/motors, running shafts through them with the sorts of seals used on drive and rudder shafts.

5

For protecting electronics, I'd look at food and medicine containers like Tupperware and its competitors.

Personally, I'd look at small Pelican-brand cases, and perhaps even potting the electronics in silicone or epoxy. Motors are a whole 'nother beast...

6

Yeah how do you water proof motors? Building a speed boat sounds fun! I already made a speed controller for a dc motor, now I just need a use. This sounds like a bit of a challenge! Here's my site for the dc motor this: https://sites.google.com/site/arduinosoapy29/motor-speed-controller :smiley:

7

Hi I like the tupperware suggestion - sounds right up my street, and my ply mounting can fit in the cake box :).

I had a look at the Pelican cases - and they seem quite elaborate and large!

There is a way still to go, but summer is also some distance away.

One point I would make is that with movement all seals will leak a little and it is best to plan for that.

So I intend to ensure that wires coming from outside follow a double S path to the electonics so that the water on the wire dosnt just slide along to the board but drips into a bilge area within the water proof container.

And the bilge has some cloth to soak it up..

I still do not have a plan for the motors, because any water on the winch will tend to migrate towards the motor no matter how good the seal is.

Water resistant servos would be nice but get real expensive way to quickly for my budget.. and are not suited for the play I am targetting.

Maybe a bag of silica gel in the bilge is the right approach?

Regards,
Dave

8

Richard,
I missed your last 2:16 posts last night, I know I posted after it but I think i was already asleep.

I am of the tape and string school of engineering - ok hackery.

Thanks for your comments they have provoked more thought:

To paraphrase what I read in your comments

  • silca gel can only keep mostly dry air dry, it can not soak up the ocean.
  • I dont need to keep pressurised water out, just deal with splashes, and slow drips.

The bits in your comments that I am not sure how to implement are:

  • the o-ring; all the places I have seen them used there has been a molded fitting into which they fit
  • the long drive shaft - i can not work out how to remove the belt drive cog that came on the motors :(, so fitting a shaft coupling is two stages beyond me I think.

However, a mixture of bilges and water drains seems possible. Could you pass your eye over this and comment?

  1. have a relatively leak free hull, with a bilge pump in the hull if it leaks fast enuf to upset me during my day of playing. I expect some water carried into the winch area by the strings, and a tiny amount through the rudder seal.
    (the small toy I play with now leaks about 1/2 inch of bilge water a day, but the electric components are raised 2 inches above the bilge, so stay dry). (this sounds worse than it is, as the hull narrows towards the bilge, it would need 10s as much water to get to 1 inch in the bilge and more again to be 2 inches deep).

  2. have batteries in a sealed box in the bilges for best stability; since the batteries are rechargable just seal them in with bathroom sealant. Bend the wires in an S pattern to help them shed water from outside before they reach the seal.

  3. put some foam low in the hull and above the bilge to ensure the boat floats when swamped. I think my toy would actually sink as it has a weighted keel and no pasative bouancy.

  4. have isolated plastic boxes with control circuitry placed on the mid line of the hull so they lie above the swamped water line - each box with a drain hole in the bottom that drains into the central bilge, so water that follows wires into the box drains into the bilge. Again use S patterns between the box entry and the boards to shed water before it reaches the boards.

  5. for the motors... use a drive cord to deliver the torque from inside the box at midline to the winche barrel mounted below them. Most of the water should follow the sail control cords onto the winch and drain into the bilge. Only a very small amount of water should transfer onto the drive belt to the motor. A thin plastic spray barrier between the drive cog and the motor should convince any that does make it into the motor box to fall to the bottom of the box and drain out the bottom.

ok enough of the elaborate plans for now,

Thanks very much for the suggestions,
Dave

9

i can not work out how to remove the belt drive cog that came on the motors

If there's no visible setscrew, they could be press-fitted. There are miniature versions of the automotive flywheel puller available. If th cogs are big enough, you could also drill and tap a couple of holes in them to kluge up something like a steering wheel puller.

10

The smartest friend I ever had, Dr Kip Turner, once defined a waterproof enclosure as "one that leaks faster at the bottom than at the top", a maxim that served us well. Context was electronics mounted outdoors, but the extreme reliability of gravity aint yer friend if a boat turns turtle.

Totally sealed = "hermetic" which aint gonna happen here, insulated wires become tiny pipes, mechanical seals ALWAYS leak. So a hobby-boat-proof enclosure might be one that "leaks slow enough to get rescued"?

About 20 ham radio guys built my Hawg Amp preamplifier to receive NASA select and tried a variety of ways to weatherproof them. Most followed Kip's maxim with small household containers and bent the cables to come out the bottom. One guy did this, then warmed the whole thing with a hair dryer and filled it entirely with hot glue. He shrugged "its finished, I'm not changing it and I dont ever wanna repair it." That was circa 1996 and last I heard it is still out his roof and working.

At the "just enough to get rescued" end of the spectrum, a worker in our plant dropped his 2-way radio into an acid bath. He grabbed a scoop and dipped it out and dropped it into the neutralizer bath for a minute, then took it to our radio shop. When the shop supervisor phoned me he had already removed the batteries. (critical!) We were skeptical but I advised him to rinse alternately in distilled water then alcohol, then dry it out over the weekend. The radio was fine.

One last practical tip, there is a gel used to waterproof cables and splices intended for direct burial. If you have ever opened up a scrap of 200 pair underground phone cable hoping to get some breadboard wire, then that "gorilla snot" that you couldnt get off your hands for 3 days is the stuff you want. It sticks to everything and water flees from it. Its the best Ma Bell could create, but hard to find sold as an individual product. Last summer I was able to google some and it had the additional property of tasting horrible to gnawing rodents, cant find the link now, but ' gel "flooded cable" ' in quotes will get you close.

11

Thanks for the pointer to gel filled cables.

Which deals well with capillary action between the copper and the insulation... neatly introducing a new area to plan for, and worry about :wink:

I found several links to CAT5 and CAT6 flooded cables, even speaker cable - and mostly for sale in full rolls. This seems like it would be best, but the prices where out of my budget.

This would be a good place to ask if anybody knows of off-cut lengths of flooded cable for repurposing?

I also found suggestions to terminate wires with heat-set-glue inside heatshrink cables. This is apparently called 'flooded heat shrink' in the US.

This is affordable. But I think there would be practical issues that need care to work around ..

  • it should work pretty well for solid core cables - as the outer surface of the cable is all the glue needs to reach - but solid core cables are not so flexible - and subject to fatigue. So I dont think I will be using them.

  • for stranded cable the glue would need to soak all the way into and between each strand - which sounds unlikely.

Aside: I recall from wiring instructions for cruising boats that you should use 'tinned wire' because it does not corrode. And that you should use multi-strand wire to avoid fatigue due to motor vibrations. I have only seen it in ship chandlers - and it is quite expensive and in gauges a bit too large for a model boat:).

The above sounds like i should have flooded cable as best choice, and if I can not afford it, the it gets pretty uncertain.

Perhaps, rather than stop the water doing its capillary thing by the above it would be simpler to keep the water away from gaps in the insulation...

To do that, as much as possible the wires are run from inside a spray proof housing to inside another spray-proof housing, with no joints outside where the water is free to move.

Where a joint is required outside a housing cover the joint with hot melt glue and heat-shrink tubing, so the copper is not expose to the water.

Sounds simple.

Will probably not work so well when the boat capsizes; so should use heatshrinking and glue on the ends inside the housings as a limited form of insurance if the turn-turtle case ends out with water in the casing - even though I know it wont be perfect.

Dave

12

Someone asked how to waterproof motors early on..

I got an answer from a retired physicist and Ham guy.. a bit depressing as answers go.

He said - you dont. The wire (in the coil (inside an average motor)) is covered with a thin insulation. The insulation cracks due the wire expanding and contracting as it gets hot under load and then cools down again.

This is not a problem when the motor is in the dry, as the cracks just fill with air and the air gap is enough insulation to stop shorts across the turns of the coil.

But when the motor is in humid conditions, especially salty humid conditions I think, the water and the copper get together and the copper corrodes.

And the next time the motor is used that bit of the wire gets hotter still, and more cracks happen and more corrosion happens and more heating and so on.

Leading to early motor death.

So apparently you should buy water proof motors where the insulation is better and the above does not happen.

Given my cheap approach - and that I have several cheap not waterproof motors...

I am thinking of reducing the factors outlined in the story above...

First - reduce the heat in the motor

  • keep the motor from heating up by not overloading it.
  • keep the motor cool by having a heat exchanger in its container to put the heat into the pond

Second - reduce the humidity in the motor

  • restrict the air flow into the motor container AND
  • arrange for the condensation from the the heat exchanger to drip into the bilge

It does sound pretty complicated to me, so I am going to price water proof motors to see what the cost actually is.

Dave

13

Thought i would add my 2cents to this conversation.

I'm currently putting together an arduino boat project as well and have been looking into the whole waterproofing idea.

If you want to waterproof just the servo's check out this link...

There's some fairly useful stuff there.

As regards waterproofing a motor, i would suggest placing the whole motor in a enclosure of a similar size with an ip rating of at least IP65. Then drill appropriate holes for wires and prop shaft output, but make the output hole large enough to take a model shaft seal, then epoxy in the shaft seal, seal the hole for the wires with epoxy, allow to cure, then submerge the whole lot in non-conductive oil (light silicon oil possibly) and put the lid on the enclosure.

Depending how hard your motor runs you may have some overheating issues, this should be solvable by increasing the size of the enclosure and in doing so increasing the heat-sink capacity of the oil. prom my experience a motor should run happily with winding temps. 50-60°C without any problems at all. If you really are having worries about temps. change the oil out for de-ionized water, it non-conductive and regularly used to cool huge electric motors on ships with a diesel/electric setup. Its also really cheap and can be picked up from any auto-factor.

As regards the actual arduino/electronics side of things my first thought was once the whole thing is made and out of the prototyping stage i would simply dunk the whole thing in a tub of epoxy resin, take it out and let the excess drip of and you should be good, but this is a very permanent option, an alternative would be to use a similar technique to waterproofing the motor, you'll just have to clean off the oil each time with some de-greaser.

If you leave the entire lot to soak in a light silicone oil for some time before using it you should be able to ensure that all the wires in the setup are all full of oil as well.

Just a couple of thoughts, please shoot me down if epoxy resin is bad for PCB or chips!!!!

14

found cat5 flooded cable by the foot at

http://www.altex.com/Cat5e-Direct-Burial-UTP-Gel-Filled-Data-Cable-VDC5-4DBG-P148569.aspx
but minimum and shipping might be unattractive.

ebay has 40ft for $25 includes shipping
http://compare.ebay.com/like/190296993276?ltyp=AllFixedPriceItemTypes&var=sbar&rvr_id=201396285533&crlp=1_263602_304662&UA=%3F*F%3F&GUID=533e824812b0a02681f669a6fffff9a3&itemid=190296993276&ff4=263602_304662

The most economical is several boat hobbyists could join together in buying a spool...

15

I've been thinking of making an rc Battleship using an Arduino as a receiver in the hull and came across a couple sites about waterproofing while doing research that might help you out(due to the fact that this is my first message they'll be in the next one)

16

for waterproofing enclosures for electronics

under waterproofing it shows you how to water proof servos and his opinion on certain motors

hope this helps