Hello! First post!
A note on your previous method: Mineral oil is commonly used to degrease things like bike parts, or your hands after working on you bike
. You dissolved the stock lubrication when you added mineral oil t your servo... oops!
I am working on my first robot (freeduino based mini sumo), but used to do quite a bit of RCing, and I have a method that I know works well. It's mildly more complex than your mineral oil, works on the same principles... And one solution was even easier to find than mineral oil
I used to fill my servos with various greases. The right grease will:
*Prevent water from leaking in small cracks, such as servo case splits and output shaft holes- even if the shaft is constantly rotating
*Insulate electronic parts (electronically- dunno about thermally)
*Lubricate moving parts
One of the most common ones I used was... Vaseline
, or generically, Petroleum Jelly. Found in most homes, and just about any convenience store, drug store, grocery store, etc.
I also used dielectric grease (ask for it at your local auto store), and there's plenty of stuff McMasterCarr has (if you make stuff, you better know McMasterCarr!). While not as instantly gratifying as going to the local shop, MMC does deliver incredibly quickly. You can access their online catalog at http://mcmaster.com
. Grease can be searched for on the left, it starts about page 2085 in the catalog.
If you are using non vaseline, look for something hydrophobic. Hydrophilic will attract water. Next look for something water insoluble. Water soluble means once water hits it, it will start dissolving away. Look for something thick. Mineral oil was on the right track, just too viscous. Vaseline lubricates, but it also STICKS. Also you of course want something dielectric, or insulating, so your waterproofing doesn't do what you're trying to prevent water from doing.
You can thin down stuff that is too thick t easily apply, just remember it will re-congeal to the original thickness, so something like parrafin wax (candlewax) would NOT work, or at least well. The best way to do this is scoop some in a glass cup or jar (be willing to dedicate it to this purpose). Then put that in a pot of boiling water. Heating the oil directly (such as on a stove) can cause a fire, so don't do that. Microwaving will probably work, too, but I can't recommend it as I haven't tried it.
You don't need to fill the whole servo. I usually completely cover the circuitry, any vents in the motor, and lather it inside where the output shaft leaves the casing. Don't put it inside the motor, the thickness will slow it down.
Keep in mind the grease will get runnier with heat when looking at options, high use situations will require more re-applying.
I have used this method down to about 2.5 feet of water, and I am willing to bet if properly lathered on, it can go to about 6-8 feet underwater, possibly more (with increasing risk of failure). I usually had to re-apply vaseline to the output shaft section every 2-3 mud races with my RC car (where it would get completely submerged in mud)
It's not the best high use long term option, but it more than worked in my tests.
If you're going to MMC to check out what they have, the dielectric greases will be more than enough resistant for our low voltages. Marine grease will also work. In the about grease section, you can find lots of info about the types/chemicals, thicknesses, etc.
The last tip I have is to get some silica gel (you get it in your shoes when you buy them, some jackets, some food packages). It's the little white packets that say do not eat. They absorb moisture from the enviroment. I'd crack open a packet, take a few beads, and glue them inside the case well away from the gearbox. They'll attract and absorb any moisture that does make it into the case.
let me know if you have any improvements!