Waterproof servos

I have been looking at ways of connecting servos to my subs control surfaces and its very difficult to place them where you want due to the way the sub coming apart, you have to route everything through the rear bulkhead.

So what would make things radically simpler is if I just mount the servos next to the control surfaces and waterproof the servos. I have seen a few ideas and videos on how to do it, the best method i have seen is to conformal coat the pcb to seal it then fill the servo with oil and seal it up with epoxy or liquid insulation. My plan is to take an already "waterproof" servo, this just means that its got rubber gasket around the shaft and seams so if i fill it with oil the seals should keep the oil from leaking out around the output shaft and and il apply some liquid insulation around the wire and seams just to be sure.

To fill it I'm thinking of placing the servo in a vacuum chamber submerged in mineral oil, il loosen the screws to let the air get out, its the only way I can be sure that the oil has got everywhere in the servo with no bubbles of air, if any air is left it will compress and let the water in.

has any one else here attempted to waterproof a servo ?

these are the servos im probably going to use, they have rubber seals around all the casing joins and around the output shaft, I use them in almost all of my boats.


https://hobbyking.com/en_us/hobbyking-hk15139d-standard-waterproof-digital-servo-5-5kg-0-18sec-41-5g.html?___store=en_us

Those look pretty good and they are cheap enough.

I have never felt very happy with my few attempts at waterproofing servos. The difficult thing with any servo waterproofing is can you guarantee no water has got in? Will it work when you use the sub next week??

(When I bring my subs back home I never leave the WTC sealed up - I open them up to let any water evaporate.)

Probably best to regard the servos as disposable and used for less vital functions - planes would just about fit into that category but rudder perhaps not.

David

I have always just treated "waterproof servos" as more splash proof, I very much doubt that they are pressure sealed good enough to take any kind of depth. This is why in thinking of filling them with oil, that way there is no air to compress so the water can't just push it's way in as the oil is incompressible. I'm looking at waterproof servos to fill, not to keep the water out but then oil in. As long as the oil stays in then it should last. But for it to work all the bubbles have to be removed from the servo in order for the oil to get into all the spaces, if you don't do this then any pockets of air are going to get compressed when it dives, causing a pressure differential allowing the water to push past the servo seals into the servo.

I have the feeling that deep diving research subs use oil filled equipment for this reason.
(Really deep diving subs have to be careful with oil because it ignites with any oxygen on the Diesel principle!)

Sounds messy but if you can get it work it would do us all a favour.

It's interesting that more and more modelers seem to be putting gear (motors etc) in the "wet". (Ref: the very nice Resurgam model on the Facebook site)

Brushless motors are pretty common outside the sub as they are pretty much already sealed as all the windings are glazed. Its just the bearings you need to worry about but even then your not putting hundreads of hours on it so it's probably fine as long as you don't let it rust.  Servos on the other hand have a lot of parts that are sensitive to water, the pcb, the potentiometer, and a brushed motor. So it makes them much more prone to damage. The PCB is easily sealed with conformal coating but the potentiometer and motor are much harder to deal with and the only thing I could think of is oil.

Im going to order some servos in the next few days for testing.

Assuming the use of a DC motor (reasonable as hey are much easier to control & cheaper) the problems is the wiping contacts in the motor (brushes) and the wiping contact in the position feedback potentiometer. Having pressureised oil coul force the oil in between the wiping contacts and effectively insulating them.
The electronics could be made conatctless using AC motors and hall effect sensors, but it would be more expensive, and I'm not sure how small an AC motor you could get.
In these days of 3D printing it would be interesting to re-make the outer shell but with a shaft seal round the output shaft, just as round the prop shaft or control rods. the only penetrations are the wires & the shaft.
If you wanted a challenge RS used to do a range of pneumatic odds & sods, may be use a small servo in the WTC to control a pneumatic/hydraulic valve with the actuating cylinder in the wet. I supose the pressure pump would be the issue and the extra space.
fun to play though!

SimonH wrote:Assuming the use of a DC motor (reasonable as hey are much easier to control & cheaper) the problems is the wiping contacts in the motor (brushes) and the wiping contact in the position feedback potentiometer. Having pressurised oil could force the oil in between the wiping contacts and effectively insulating them.

A lighter alternative could be something like silicone lubricant or WD40, they could work better if a heavier oil is an issue.

I had a look at the servo on the facebook page,
it says on the page that "This servo was kept under 1 meter of water for 1 week during testing.."

If your running 2.4ghz or a dynamic diver 1m should be fine. I would still want to fill them with something just to be sure if going past 1m as its now into uncharted territory lol


https://www.rcmodelz.co.uk/k-power-waterproof-16kg-metal-gear-servo.html?fbclid=IwAR3ncdUuc6XIgT2HBGerCRuDQSepyB_-LNFRLO-eXYn8OzE7L878otRRUl8

https://youtu.be/1tuVSDnOcXQ

redboat219 wrote:https://youtu.be/1tuVSDnOcXQ

I believe this is the servo he is using and he is right about it not being cheap at around £40

https://www.ebay.co.uk/itm/333342778981

Revell 1/72 Type VII using servos and brushless motor in the wet. Servoes are filled with oil.
https://youtu.be/yCVMhPmrKEw

I have ordered a pair of the hobbyking waterproof servos for experimenting with, I will test one stock to see how well sealed it actually is, then I will fill them with oil.

I have submerged one to test, it's not running but if it's still dry inside when I disassemble it tomorrow il repeat the test but connected to a servo tester.

Well that was a failure, I opened up the servo today and it was full of water, since it wasnt connected to power there shouldnt be any damage so im going to let it dry out then try again but this time im going to apply some silicone grease around the openings as they looked totally devoid of anything. If that fails, I'm just going to fill it with some kind of oil then seal it.

I have covered all the rubber seals with silicone grease and submerged it again. The seals were all  dry of grease so I think that a little grease might be all it needs. If this fails then the next step is to fill it with something.

Cracked open the servo today and surprisingly it was bone dry inside. All that I changed was adding a little grease on the rubber seals