Hopefully this is the right place to ask. Recently, after I finished a sentry gun, I begun working on an Arduino-based small-scale boat, respectively an imitation of the USS Langley made out of wood which will be roughly the size of a two-door Smart, but definetely longer. I plan on using a GPS shield to have it sailing on its own following a defined path. The hard part is building the actual ship and mounting the servos. I was planning on buying two (or only one, if enough) Hitec HS-5646WP Waterproof High-torque digital servomotors for moving forward and another smaller one for the steering gear. I will also try to have the flight deck smooth enough for having a radio-controlled warbird take off and land on her. I can say I'm very enthuastic about this project. My question is, how do I manage to waterproof the Arduino AND the car battery that will be used for the power supply? Also, any advices on the project itself are well appreciated.
Lead acid batteries generate gas and therefore need to be in a box and vented to the atmosphere through a tube or one way valve.
The other electronics needs to be potted using something like the Raytech silicone gel shown here. https://www.youtube.com/watch?v=1wneV-tLOHo The "power gel" variant is re-usable to some degree although the demo in the video isn't totally convincing.
In Australia there is also a product called "Selleys All Clear" which is essentially synthetic rubber dissolved in toluene. This sticks to most things, but takes days or weeks to fully cure as the solvent has to evaporate. This is OK for waterproofing wiring connections but the solvent may harm other materials.
Don't use general purpose silicone from a hardware store, or moulding silicone. The cured silicone doesn't have enough residual tack to keep water out. It may look ok, but once you start applying mechanical stress it just peels away.
Don't use styrene fibreglass laminating resin as a potting compound. It has a high shrinkage rate and will mechanically stress the components on the circuit board.
Also, the cheapest waterproof connectors that you can buy are the ones used for outdoor solar powered lights. They don't have an IP rating but they do have silicone rubber o rings and a threaded lock ring. Connectors that do have an IP68 rating are extremely expensive, way more costly than the materials used in their construction.
The latest thing I've been looking at is called "on and off" glue which is a brush applied pressure sensitive acrylic adhesive similar to the adhesive used on post it notes. It sticks to most things keeping water out and retains it stickiness over many years.
As you may already know, nothing sticks to acrylic except solvent based adhesives. Using the wrong solvent will cause the acrylic to crack. Any kind of seal you need to make to acrylic will need to be mechanical in nature.
Thanks a lot for the fast answer. The Selleys All Clear sounds promising and, providing there are ways to purchase it here in Romania, it will probably work excellent in having the port and the starboard glued togheter. No matter how much it takes to dry out, I’m in no hurry, although I will try and use screws for the stirn and the front of the ship, if possible. To have the flight deck in place, normal silicone may work well, as it will be above the water. I’ve also found some nice-looking waterproof connectors and cables, just perfect for the submerged parts of the ship.
Time will tell if this will work. I will begin work as soon as I have wood and a suitable adhesive or silicone, providing there are absolutely no ways of getting my hands on that Selleys All-clear thing. The on and off glue sounds worth checking out aswell. To reduce effort, I’ll do my best to have the Arduino mounted somewhere above waterline. The battery may be a problem aswell, though.
I’ll do my best to keep ya in touch with the project using this very thread. Thanks a lot for the hints, once again.