Waterproofing servos

[Monahan Steam Models]

Spent a good part of the day screwing around with trying to make some $2 servos waterproof.



This sorry subject has been sealed at the seams with rtv and has holes drilled into each cavity to allow air and liquid to pass between. It’s been filled with mineral oil but I can’t seam to get every last air bubble out after hours of work. Been fiddling with it for hours. Have subjected it to a vacuum chamber to get rid of the last few air bubbles but with no significant luck.

There has got to be a better way. Trying to avoid stepping up to the large sized bodied micro servos.

[Scott T]

How about settling both pieces in a pan of mineral oil vacuuming then slide pieces together under oil surface.

[He Who Shall Not Be Named]

Spent a good part of the day screwing around with trying to make some $2 servos waterproof.



This sorry subject has been sealed at the seams with rtv and has holes drilled into each cavity to allow air and liquid to pass between. It’s been filled with mineral oil but I can’t seam to get every last air bubble out after hours of work. Been fiddling with it for hours. Have subjected it to a vacuum chamber to get rid of the last few air bubbles but with no significant luck.

There has got to be a better way. Trying to avoid stepping up to the large sized bodied micro servos.

fill a container 1/4 full of mineral oil. Fill the servo with oil then plunk the servo (with one side featuring a 3/8-inch diameter hole) into the oil. Weigh it down with something so it's totally submerged. Pull a hard vacuum (at least 28-inches of Mercury). Get things back to one-atmosphere and, with the hole facing upward carefully remove the oil-soaked gadget. Clean the face of all oil and glue down a disk of very pliable rubber sheet over the hole, making sure that you don't entrap any air as you do it.

The hard vacuum is the only way to saturate the motor and potentiometer. That's where the air gets trapped on a gravity fill.

Done. You're now the proud owner of a pressure compensated oil impregnated whatchamacallit. The Marina Trench awaits! Start the SEAVIEW music.

[Monahan Steam Models]

fill a container 1/4 full of mineral oil. Fill the servo with oil then plunk the servo (with one side featuring a 3/8-inch diameter hole) into the oil. Weigh it down with something so it's totally submerged. Pull a hard vacuum (at least 28-inches of Mercury). Get things back to one-atmosphere and, with the hole facing upward carefully remove the oil-soaked gadget. Clean the face of all oil and glue down a disk of very pliable rubber sheet over the hole, making sure that you don't entrap any air as you do it.

The hard vacuum is the only way to saturate the motor and potentiometer. That's where the air gets trapped on a gravity fill.

Done. You're now the proud owner of a pressure compensated oil impregnated whatchamacallit. The Marina Trench awaits! Start the SEAVIEW music.

I started to mess around yesterday with the thin rubber membrane disk for the pressure compensated feature like you suggested the other day. Had a bag of new party balloons and made a gasket punch to stamp out the disks. Haven’t tried using them yet as I wanted to first start with attempting to fill the servo with the oil.

Yes sir indeed the motor is a area where air can be trapped. I drilled small holes inside the servo’s plastic case where existing holes in the motor case where located to allow air to escape and oil to enter.

Perhaps I was not pulling enough vacuum on the servo inside the jar yesterday to make enough of a difference. It did help to get trapped air out but not enough. I was only able to pull about 23-inches of Mercury with the hand actuated mighty-vac tool that I was using. (Much smaller and easier to use at the kitchen table than the vacuum chamber down in the shop) The bell jar dome on my vacuum chamber machine has a crack in it from someone dropping something on it years ago but perhaps it’s time to try to fix that.

[He Who Shall Not Be Named]

I started to mess around yesterday with the thin rubber membrane disk for the pressure compensated feature like you suggested the other day. Had a bag of new party balloons and made a gasket punch to stamp out the disks. Haven’t tried using them yet as I wanted to first start with attempting to fill the servo with the oil.

Yes sir indeed the motor is a area where air can be trapped. I drilled small holes inside the servo’s plastic case where existing holes in the motor case where located to allow air to escape and oil to enter.

Perhaps I was not pulling enough vacuum on the servo inside the jar yesterday to make enough of a difference. It did help to get trapped air out but not enough. I was only able to pull about 23-inches of Mercury with the hand actuated mighty-vac tool that I was using. (Much smaller and easier to use at the kitchen table than the vacuum chamber down in the shop) The bell jar dome on my vacuum chamber machine has a crack in it from someone dropping something on it years ago but perhaps it’s time to try to fix that.

I'll take an implosion over an explosion, every day! Nothing some Duct Tape won't fix. Start the machine and step outside for some air and listen for an 'event'.

Yeah, to get those pesky bubbles to froth out you got to exceed 28-inches. I love the party balloon diaphragm! It doesn't get more flexible than that.

I love your work, Nick. You're scary good. A real, honest to God Machinist. I'll have to have you killed someday. Sorry.

David

[Monahan Steam Models]

I'll have to have you killed someday. Sorry.

David

Ha! No worries, it comes with the territory!

I’ll give the servo work another go today but this time using the vacuum machine down in the shop pulling at least 28-inches of mercury as you point out, thank you! Will also submerged the servo in a container with oil inside the vacuum chamber. I was considering glueing the rubber compensation diaphragm to the servo case prior to introducing oil into the process to ensure a good bond and no trapped air bubbles behind it. Does that sound good?

The fill/vent holes that I drilled in the case were about .060”. These holes seemed to work well injecting the mineral oil into the case for the initial filling and venting. Using a larger hole to fill, vent and pull vacuum through as you described would definitely be a lot easier but sealing that hole later with the balloon diaphragm could be tricky without trapping air. Wondering if pulling vacuum on the .060” holes will be enough to do the trick?

Nick

[He Who Shall Not Be Named]

Ha! No worries, it comes with the territory!

I’ll give the servo work another go today but this time using the vacuum machine down in the shop pulling at least 28-inches of mercury as you point out, thank you! Will also submerged the servo in a container with oil inside the vacuum chamber. I was considering glueing the rubber compensation diaphragm to the servo case prior to introducing oil into the process to ensure a good bond and no trapped air bubbles behind it. Does that sound good?

The fill/vent holes that I drilled in the case were about .060”. These holes seemed to work well injecting the mineral oil into the case for the initial filling and venting. Using a larger hole to fill, vent and pull vacuum through as you described would definitely be a lot easier but sealing that hole later with the balloon diaphragm could be tricky without trapping air. Wondering if pulling vacuum on the .060” holes will be enough to do the trick?

Nick

No problem with the small holes as the froth will work its way out of there like an Octopus. If you entrap a bubble of air during the diaphragm install, just come back with a hypodermic, punch the needle in the rubber and extract the bubble. The rubber should self-heal (if not, go to a thicker rubber or one with the properties of the rubber caps on those little glass bottles used to hold medicine designed for hypodermic use.




David

[SubDude]

I just fill them full best I can with CorrosionX with a syringe and I don't worry about any trapped air. I have rarely had any problems with them outside of their natural cheap servo issues.

[Mooneyjock]

For what its worth, I once was at a major model airplane show, and a booth was selling receiver and servo water proofing oil. They had a bunch of servos hanging inside a fish tank filled with water working happily away. They weren't filled with the oil, but just had all the insides coated with it. After talking to them a while, it turns out the oil they were selling was actually an aviation anti corrosion product called Corrosion X. It is available in spray cans from aviation supply companies like Aircraft Spruce and others. Might be worth exploring.

John
"Now here's another fine mess you've gotten me into."

[Mooneyjock]

Oop's I didn't read the preceding post to mine, which pretty much says the same thing.

[He Who Shall Not Be Named]

For what its worth, I once was at a major model airplane show, and a booth was selling receiver and servo water proofing oil. They had a bunch of servos hanging inside a fish tank filled with water working happily away. They weren't filled with the oil, but just had all the insides coated with it. After talking to them a while, it turns out the oil they were selling was actually an aviation anti corrosion product called Corrosion X. It is available in spray cans from aviation supply companies like Aircraft Spruce and others. Might be worth exploring.

John
"Now here's another fine mess you've gotten me into."

That's right, it was repackaged and sold to us as, Stumph(spelling?). Trouble is that the mist coating won't get into the motor brushes or commutator, or potentiometers wiper and resistor pad -- check those servos come the second season of use. Do they still work? Doubtful.

(Love your signature line).

David
****ing on Parades

[Monahan Steam Models]

For what its worth, I once was at a major model airplane show, and a booth was selling receiver and servo water proofing oil. They had a bunch of servos hanging inside a fish tank filled with water working happily away. They weren't filled with the oil, but just had all the insides coated with it. After talking to them a while, it turns out the oil they were selling was actually an aviation anti corrosion product called Corrosion X. It is available in spray cans from aviation supply companies like Aircraft Spruce and others. Might be worth exploring.

John
"Now here's another fine mess you've gotten me into."

Hey John,

First of all welcome to the forum.

I picked up a can of the corrosion-x last year for use in the servos after other members here have had good success using it in their servos. I have not completely decided on sticking with using mineral oil or trying the corrosion-x at this early stage.

I chose to start this experiment with filling the Servos with mineral oil because it is commonly used in similar applications and as David M points out it may flow easier into some of the harder to reach areas like the motor and potentiometer as I understand the corrosion-x is a bit thicker. The goal I’m looking to achieve a 100% fill with zero oil leaking back out of the servo. The 100% mineral oil fill if achieved should in theory counter act water entering the servo under pressure at reasonable depths. At the depths I plan to operate at(probably 10 feet max in crystal clear water), the compressibility of the mineral oil compared to the water should be almost a non issue.

Regards,

Nick

[Monahan Steam Models]

Some interesting results from today’s work on the servo. I posted them here as it is part of the type VII build.

https://forum.rc-sub.com/forum/builder-threads/156107-1-48-scale-type-viic-u-201-build/page14#post159113

Post #206 is today’s findings.

Nick

[Mooneyjock]

The neat thing about Corrosion X is that it will find its way into every nook and cranny. I use it on my r/c equipment in my model sea planes, as they get a dunking every so often.
John
"Now here's another fine mess you've gotten me into."

[RanSan]

I am testing mineral oil in my servo and dipping it into a liquid "flex seal" type product, basically a liquid rubber. I find it has a slow leak where the wires come out. I don't have access to a vacuum pump which might draw in some of the rubber and help seal it. Do any of you have experience or suggestions on how I might seal the area around the wires? Thanks