water-proofing a servo

[kazzer]

Hi! I'm new here, so please excuse me if this has already been covered, I think I've read the entire thread correctly, but senility can sometimes reign and I may have missed something.

I was passed a link to this thread by a friend who is into those battleships that fire BBs. So, he operates with many servos in the wet. 

However, I sell model static diving submarines  see www.caswellplating.com/models and keeping servos running is a big deal at 15-20 foot depths.

Our way of doing this is with a watertight cylinder, we call them Sub-drivers.


The servos, radio receiver etc. etc are housed within a Lexan tube, and the push rods and prop shaft run through a  seal
see -  http://www.caswellplating.com/models/propeller.html

These push-rod and prop seals come in 1/8" and 3/16" diameters. If you aren't dealing with something as complicated as a static diving submarine, you could easily make the tube from any plastic pipe, and turn up a couple of end-caps.


I hope this helps

[Admin]

I guess its time to reply back to this post.

First, as mentioned multiple times in this thread, my actuator isn't giving me rotatory motion - I need linear motion. I also have 10 of them in use at the same time, so it has to be very reliable. Each servo pushes *two* shafts - meaning I'd have to waterproof 20 holes. If a single one fails, they all fail.

So, my solution, was to waterproof each individual servo.

Anyway, I run the servos all the time underwater at about 2 feet depth. They fail at a rate of one servo every 5 hours or so . . . but probably cause servos aren't that reliable anyway . . . I just replace the servo and and my robot back into the water. Each servo is only $13 and funding isn't a problem for me.

[culturedropout]

How about magnetic coupling?  Aquarium filters used to (and maybe still do) use that method to let the motor (on the outside) turn the impeller (in the water).  They just used a small bearing and a magnet in the impeller, and a magnet mounted on the end of the motor shaft such that it lines up with the one on the impeller.  They couple to each other through the thin plastic case of the filter.  I'm not sure how much torque you could transmit this way, but with good magnets I would imagine quite a bit.  As a bonus, it would keep your servo from stripping its gears if the output got stuck; the magnetic coupling would just "slip".  Has anyone tried this?

[nac]

I've seen your video and don't think your approach to waterproof the servos with oil is a very good idea, at least with standard (low-cost) servos.
The problem is that standard servos use low-cost brushed DC-motors and it's hard to prevent the oil from going into the brushes. Once it gets between the brushes and the commutator, then the insulation properties of the oil causes problems. Besides that you also have increased drag since you'll be rotating some amount of oil. Bottom line is the servos may work for some (long?) time but they will eventually lose power. If you search the web you'll see lots of DC motors filled with oil to withstand immersion in underwater robotics applications (up to thousands of meters!), but they will all be brushless. Recently, Futaba started making some servos using small brusless motors (eg. BLS352), but unfortunately they are much more expensive than stardard ones. Now I think these could be filled with oil...

BTW it seems in the video that you may use any "silicone" to seal the electronics side, but be aware that standard-grade silicone contains acetic acid which can cause corrosion in particular to electronics/copper/etc. So you can only use *some* RTV rubbers for waterproofing electronics.

Regards
nac

[Admin]

Just an update . . . I've waterproofed like 50 servos already using this method. The futabas occasionally fail, but I never investigate why. Maybe gears strip, or circuits rust, I don't know. Most last months underwater, which is long enough for what I need to do.

One of my Hitec servos has lasted like 2 years after being waterproofed!

BTW it seems in the video that you may use any "silicone" to seal the electronics side, but be aware that standard-grade silicone contains acetic acid which can cause corrosion in particular to electronics/copper/etc. So you can only use *some* RTV rubbers for waterproofing electronics.

Yea I didn't realize that until a few weeks after I made that video. I now use 'electronics grade RTV' without a problem.

[hoosier122]

i reassembled the servo in a jar of oil, fully submersed. lemme tell you how hard it is to reassemble a servo in a light refracting jar of messy slippery oil while wearing gloves . . . lol damn thing took about 30+ minutes to put back together haha

didnt help when all the tiny gears decided to leap out of the servo . . . or that screwdrivers are impossible to rotate when your hand is oiled up . . .

then the oil kept leaking out so used lotsa super glue . . .

i guess it was a 2 hour process, plus a month trying to figure it out . . . but i think you can do it in like 30 min following the tutorial i will write up . . . ill point out all the mistakes i made so others wont make em . . .

but generally, im very happy with the final product. couldnt have done it without everyones suggestions! 

ocean going solar powered bot, using GPS to navigate that would send a text message with it's location when it got close enough to shore

So did I! (minus the text messaging part) Meant to do it years ago . . . tried recently on my new robot boat i made a few weeks ago but alas the chassis was too unstable for large waves and high winds . . .

Try using a syringe in the future.

[Admin]

Try using a syringe in the future.

Won't work, I've tried. But this doesn't rule out drilling a small hole, then using a syringe with oil, and finally sealing that hole.

[Razor Concepts]

This guy doesn't just plasti-dip the circuit board... he does the entire servo!
How to Waterproof an RC Servo - RC ADVENTURES

[Admin]

I just tested my waterproofing method to 30 feet depth on several servo types a week or two ago. The water is de-ionized, and they were left underwater for about 24 hours.

All the servos still work!

However the servos were unpowered. I'll be testing them again while powered and rotating sometime in the next few weeks.

Oh, and this is the RTV I'm currently using:
http://www.societyofrobots.com/robotforum/index.php?topic=8396.0

Amazing, I started this thread almost exactly three years ago and it has been read over 20k times . . .

[Razor Concepts]

The company I intern for develops UUVs and they have used these in the past:
http://www.volz-servos.com/en/products/specialapps_submersible.php?m=m

Although now they use a pressurized oil system to protect all of the electronics, so those servos fell out of favor.

[NGuggemos]

We might need to water proof our servos too. I don't really have any suggestions, but I am going to try whatever you try.