Society of Robots - Robot Forum

Mechanics and Construction => Mechanics and Construction => Topic started by: Admin on July 20, 2006, 09:05:10 AM

Title: water-proofing a servo
Post by: Admin on July 20, 2006, 09:05:10 AM
Does anyone have recommendations on how to water-proof a servo for full submersion?

I called both Futaba and Hitec, and both said "none of our servos are water-proof" but "many are water and dust resistant."

"They cannot be submerged."

I have also seen the balloon method, the fill the servo with grease method, and the plastidip method . . . but they all kinda suck . . .
Title: Re: water-proofing a servo
Post by: Gopher on October 02, 2006, 01:45:10 AM
Could you possibly encase the servo inside a larger, water-tight case? the servo movement could be transmitted by a rod passing through a tight rubber neck. If it's a continuous servo, parts must exist, perhaps something scavanged from a cheap toy rc submarine?

Not sure if this will help, but it seems nobody else has any ideas...
Title: Re: water-proofing a servo
Post by: Admin on October 02, 2006, 10:22:35 AM
So I have seen that method too, incasing it in a water tight box, using a rod, and something called a 'rubber boot.' It attaches between the rod and outer casing. I have seen pics of this rubber boot but cant find where to buy any . . . ideas?

Im thinking about just incasing the entire servo and push rod in this big blob of highly flexible liquid rubber . . .
Title: Re: water-proofing a servo
Post by: Gopher on October 02, 2006, 12:16:49 PM
Not sure; the two closest things I can think of are rubber nipples (for baby bottles) and a kind of rubber switch/button covers I've seen used on boats; nipples you can get anywhere, and pretty cheap too. The others I'm not sure but a google search for boat electronic components might turn up something. Might be able to scavenge one from a generator, or other outdoor equipment. Hell, they might sell them at Home Depot, I've never looked for anything like that before.
Title: Re: water-proofing a servo
Post by: dunk on October 02, 2006, 01:36:22 PM
so from much experience messing around in boats, any sort of rubber seal will always leak a little bit.
the further under the surface the greater the pressure so the more leakage.
this doesn't have to be a problem. you just have to remember to leave a small trap where the drips can form a pool away from your electrics.
with a boats propeller shaft the water just settles in the lowest part of the boat.

i'm curious what you have against the idea of filling a servo with grease?
admittedly the increased drag on the components inside the servo could be a problem.
many pleasure boat bilge pumps are constructed this way. the idea being they have to be able to operate underwater if you start sinking. if you open one up they are full of light grease.

hmm, this has me thinking, try looking at pleasure boat autohelm servos. i've seen these operate in some conditions that would describe as close to underwater. (they are definitely more water proof than any waterproof coat or leggings you can find.)
i imagine they would all be a bit too big for a small robot project but worth looking into for ideas on how to seal the things if nothing else.

dunk.
Title: Re: water-proofing a servo
Post by: Admin on October 02, 2006, 06:22:28 PM
Ok I didnt mention these details before because I wanted to not overcomplicate the question . . .

So there will be 4 servos in a box. The robot will have a total of 4 of these boxes, for 16 servos. Whatever I do cant take too long to impliment, as even an hour per servo is 16 hours of work . . .

The boxes rotate about 100 degrees sinusoidally, and will be under water for about 3-4 hours total. I thought of your drip idea, but in this particular case it would be risky.

I am warry of the rubber boot idea because each servo needs 2 shafts exiting the box (one shaft for each end of the servo horn), so thats 8 rubber boots per box, for a total of 32 possible leak failures  :P The box itself is only 4"x1.5"x1.5" - I must fit 8 boots on just one side.

I think I will fill the servos with grease after all (or some other low viscous non-conductive oil or jelly) as a secondary waterproofer. I am pushing the limits on current draw and servo force, so Im a little worried about increased drag on the servos - might not have an option tho . . .

To add another complication, the water proofing shouldnt thermally insulate the servo too much as I dont want it to overheat and burn out . . .

The servo I am using is the Futaba S3110. I was falsely led to believe by multiple erronous websites out there that this servo (or any servo) was waterproof, so I already have it built and working. Now just gotta fix this itsy bitsy prob . . .

Ok I realize this is really over complicated . . . If I was just making a functional robot I would never have gone this direction . . . but there is good science research that requires this and its definitely pushing my limits as an engineer!

I think I will just test out my servo in a rubber blob idea and see what happens . . .
Title: Re: water-proofing a servo
Post by: dunk on October 03, 2006, 04:01:07 PM
so i'm starting to doubt my previous post.
i'm wondering if taking a servo that is designed to run in air and filling it with grease will add too much friction to the little motor inside.

what about if you stick with your rubber boot idea but fill the space inside the boot with grease but leave the servo empty?
you said your servo was reasonably well sealed but not waterproof. i wonder if it would be well enough sealed to stop grease getting in?
this way the grease would form a barrier.
even if a small amount of water contaminated the grease you could service it occasionally, changing the grease.
if a small amount of grease found it's way into the servo there is no real harm.
a kind of messy solution but could work.

dunk.
Title: Re: water-proofing a servo
Post by: polar bear6 on October 03, 2006, 04:40:25 PM
i dont know if this helps, but you can have the servo electronics in another box than the servo, so you only have to wory about waterproofing the motor itself.
Title: Re: water-proofing a servo
Post by: Admin on October 03, 2006, 05:19:46 PM
ok next question, anyone know of any non-conductive low-viscous grease i can use?
servo grease is too thick, i think . . .

just a weird off the wall idea, maybe i can fill the servo up with de-ionized (non-conductive) water to balance the fluidic pressure, and use a simple o-ring seal to prevent small leaks . . . fyi, de-ionized water is cheap and easy to get . . . too bad i cant just fill up an entire swimming pool with it . . .

as for the electronics, since its in a seperate compartment that i never need to open, im just going to superglue that end shut.
Title: Re: water-proofing a servo
Post by: Gopher on October 03, 2006, 06:04:50 PM
Saw a computer mod where they tried filling the case with distilled water. It didn't work, and ultimately they used vegetable oil instead, which worked great. I believe they ultimately recomended motor oil instead of vegetable?

looking for the link... here it is. (http://www.tomshardware.co.uk/2006/01/09/strip_out_the_fans1/) They describe their problems and solutions in detail, might be helpful.

[edit:originally said mineral water instead of distilled water - big difference!]
Title: Re: water-proofing a servo
Post by: dunk on October 05, 2006, 09:26:46 AM
so the lightest grease i can ever remeber seeing was meant for high performance bicycle bearings.
i think it was referred to as "white lithium grease" and doing a search on the net seems to confirm this.

interestingly, doing a quick search for bicycle grease on the net i found some guy sugested partolium jelly (ie. vasaline) in his bicycle hubs.
that might just work for you as well. it's definalty very water resistant, non cunductive and not too thick.

dunk.
Title: Re: water-proofing a servo
Post by: megaman935 on October 05, 2006, 06:36:05 PM
If I need something, I always check ebay when I can't find just what I want. They usually have what I want....... Just a suggestion on the 'rubber boot' thing.... :-\
Title: Re: water-proofing a servo
Post by: Admin on October 05, 2006, 10:02:12 PM
whoa good ideas!!!
man that cooking oil idea . . . totally whack, but i think its just what i want.

i have access to lithium grease too, as it comes in this spray can foamer thing to grease up tools for our CNC.

time to experiment  ;D

maybe around christmas ill write a really good tutorial on waterproofing servos, after i test and try everything out.

so i just spoke to a friend of mine about the oil PC, and he said mineral oil would work better than cooking oil . . . but ill look at both
Title: Re: water-proofing a servo
Post by: Gopher on October 06, 2006, 12:08:17 PM
Hope it works out :)

The guys that made the oil-cooled computer admitted vegetable oil was a poor choice, and that they used it in their test because it is cheap, readily available, and proved the concept well enough.
Title: Re: water-proofing a servo
Post by: Gopher on October 09, 2006, 11:23:47 PM
Hey, you were asking about the snake robot vid because of your water-related project, and it got me thinking. Have you concidered not waterproofing your parts at all, but simply putting them together in a flexible, waterproof container? It doesn't even have to be a container, it could simply be a waterproof latex skin; you just build the bot ignoring the water, just giving it the right shape and movement, and then wrap it in a watertight skin. If you vacuum the air out with a pump when sealing it, it would keep water out far better than a rigid air-filled case.

No idea how you'd make a custom-shaped latex skin, but latex is just an example. I'm sure there's an appropriate textile out there which can be tailored into custom, water-tight shapes.
Title: Re: water-proofing a servo
Post by: Admin on October 10, 2006, 09:52:13 AM
That was actually my first idea, but it had leaks. I was never able to make a perfect seal around the protruding parts.  :-\
Title: Re: water-proofing a servo
Post by: Admin on October 10, 2006, 11:09:39 AM
Browsing some more for ideas I found someone suggesting putting vasilene around the output shaft of the servo, followed by a coating of silicone oil, claimed to work 'for up to 5 foot of water.' Perhaps it can be filled with de-ionized water for extra measure . . .

So I cant think of any clean way to fill a servo with the oil, other than assembling it while submersed in a cup of it. Hmmm I also have to keep the oil from getting in the motor to avoid adversely affecting the torque . . . And I think the very first gear that comes out of the motor is extremely low torque but high velocity . . . so might be strongly affected too . . .

I think Ill just order a few servos and abuse them with all of the above mentioned ideas . . .
Title: Re: water-proofing a servo
Post by: Gopher on October 10, 2006, 02:55:44 PM
You misunderstand, I was talking about not having any protuding parts. Just a fish-shaped bot, and wrap the whole thing up.  Still obstacles to overcome, but it'd be a lot easier to get a total seal at the opening if nothing is protruding through the opening. There might be a reason this is impossible for your application, though, if you have sensors or elements that must be in direct contact with the water...
Title: Re: water-proofing a servo
Post by: Admin on October 10, 2006, 03:02:44 PM
It has a really wierd shape, like a fish. No container (or a wrapped sheet of rubber) can be easily made for that shape.

Anyone know what would be better to fill the servo with, silicone oil or mineral oil?
I cant seem to find these numbers for either - surface tension, viscosity, conductivity, and a hydrophobic comparison of both. I think either will work, I just want to quantitatively decide which is better.
Title: Re: water-proofing a servo
Post by: Admin on October 10, 2006, 03:48:54 PM
After spending hours today searching online, I came up with this info:

Mineral Oil
surface tension: 25mNm-30mNm
viscosity: 30cSt-100cSt

Silicone Oil
surface tension: 20.5mNm
viscosity: 50cSt-500cSt

I have decided on using mineral oil because:
Mineral oil is more like to be used in power transformers as opposed to silicone oil, so I reason someone has a reason for that . . . Mineral oil has a higher surface tension, meaning it is less likely to leak through tiny gaps. It also usually has a lower viscosity, so less torque resistance on the motor and gears. And lastly, mcmaster sells mineral oil but not silicone oil.

I couldnt find any info on how hydrophobic either were . . .
Title: Re: water-proofing a servo
Post by: Arislan on October 21, 2006, 05:41:58 PM
Try asking in the Subcommittee.com forum, they generally answer quite quickly.
Title: Re: water-proofing a servo
Post by: Admin on October 21, 2006, 06:12:25 PM
Hmmm useful forum for underwater robots! Will use that for research now  :)

Unfortunately couldnt find anything on waterproofing servos . . .

Anyway I ordered a gallon of oil and some soon to be victimized servos, will test that as soon as it all comes in.
Title: Re: water-proofing a servo
Post by: Admin on October 24, 2006, 12:19:53 PM
It worked!

So I put it in oil, used O-rings, superglued it all shut, and it worked!

I got videos and step by step images too  ;)

Ok so I didnt fully test it . . . put it in only 2ft of water and ran it for only 5 minutes . . . Ill give it more brutal tests when I put it on my robot . . . I estimate it to handle like 50ft+ depth, since oil filled motors are used for extreme depth deep sea diving vehicles.

A very thin oil slick appeared to float at the top surface of water . . . possibly a leak, or just leftover oil I didnt clean up when I was done . . . Slow oil leaks are my only worry for failure . . .

Ill write up a tutorial on it when I can, but might take several weeks . . .
Title: Re: water-proofing a servo
Post by: dunk on October 24, 2006, 01:13:58 PM
cool. so that must be a bit of a worry off your mind.
i'm curious, so did you fill the whole servo with the oil in the end or just part of it?

i was once toying with the idea of making an 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.
the idea has never got any further than being an idea i throw around my brain from time to time but making motors watertight for extended periods was always one of the stumbling blocks.
nice to hear it might be easier than i thought.

dunk.
(too impatient to wait for the tutorial.)
Title: Re: water-proofing a servo
Post by: Admin on October 24, 2006, 01:24:03 PM
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!  :)

Quote
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 . . .
Title: Re: water-proofing a servo
Post by: dunk on October 25, 2006, 12:36:06 PM
so i planned on making the buoyancy very low so it was practically submerged to help avoid this problem.
this was why i was so concerned about any water leaking in.

there are a few projects out there that basically drift in ocean currents.
i wanted something that could actually make way against the weather.
a sailing craft would be nice as it could still make way through the night but solar power and electric motor driven would be far easier to implement.

let me know if you ever need any input on navigation strategies.
i have a lot of small craft experience in tidal waters and ocean crossings.

dunk.
Title: Re: water-proofing a servo
Post by: JesseWelling on October 25, 2006, 02:49:03 PM
I bet if you drilled a hole through the srewdiver handle and put a screw or pin or some thing else to press your thumb against through it it would generaly be easier to use with oil. Just a quick thought I had if he's going to make alot of these.....
Title: Re: water-proofing a servo
Post by: Admin on November 04, 2006, 12:14:52 AM
Okie its done:

http://www.societyofrobots.com/actuators_waterproof_servo.shtml

my longest tutorial yet . . .
Title: Re: water-proofing a servo
Post by: Dosbomber on November 06, 2006, 03:48:21 AM
I'm wondering if it would be prudent to add a dab of white lithium grease to the gears (if that other stuff dissolves) before oil-filling the servos..

Great write-up.  Plenty of details, and always good to hear about the mistakes.  It's good to learn from your mistakes, but cheaper to learn from someone else's.   ;D
Title: Re: water-proofing a servo
Post by: JonHylands on November 17, 2006, 01:40:03 PM
Care to post some pictures or at least a more in-depth explanation of what you're doing?

I have built an AUV, and have a pretty well-documented site about it:

http://www.huv.com

- Jon
Title: Re: water-proofing a servo
Post by: Militoy on November 17, 2006, 05:39:18 PM
Just about any "grease" (thixotropic lubricant) will dissolve in a lubricant of a lower viscosity. There are several silicone-based greases, mainly by Dow-Corning, that are somewhat less soluable in organic mineral oil based lubricants - but over a short period of time, they will all succomb to suspension in the lighter oils. The point is, when the mechanism is operated under oil, there will still be adaquate lubrication - with or without the grease.
Title: Re: water-proofing a servo
Post by: Admin on November 18, 2006, 08:45:24 PM
Quote
Care to post some pictures or at least a more in-depth explanation of what you're doing?

Unfortunately I cannot, as this is an experimental research project I am working on for the Navy. It isnt confidential, but for patent and intellectual property reasons I have to be careful not to give out details.

But you are in luck, as a paper fully covering part 1 of the project will be published in April at ICRA '07. Ill post it on the site then, and finally end the mystery . . .

The general project involves building a robot fish using a special actuator. Part 1 covers the science, design, and study of the actuator. Part 2 involves building the vehicle with the actuator. We are finishing up part 1 now, just doing final verifications on our data. Part 2 has begun with our first vehicle prototype. The paper on part 2 might not be published till the end of 2007 . . .
Title: Re: water-proofing a servo
Post by: JesseWelling on November 18, 2006, 09:03:14 PM
Are you by chance working for NavSea?
I had an interview with them just a while back but they didn't seem to interested in me  :-\
Title: Re: water-proofing a servo
Post by: Admin on November 18, 2006, 10:02:14 PM
Nope . . . Naval Research Laboratory . . .
Title: Re: water-proofing a servo
Post by: polar bear6 on November 20, 2006, 11:00:21 AM
Nope . . . Naval Research Laboratory . . .

omg the admin is a navy seal!
Title: Re: water-proofing a servo
Post by: JonHylands on November 27, 2006, 04:46:20 PM
I like the idea of using bladders and valves to control underwater movement.

I imagine a mechanism without any servos - just electromagnetic or electrostatic "bellows" that pump water through the system.

Most of the AUV gliders do something exactly like this. Some even use the temperature gradient between water layers in the ocean as a power source for the pump.

http://www.webbresearch.com/slocum.htm

- Jon
Title: Re: water-proofing a servo
Post by: Admin on November 27, 2006, 08:47:05 PM
the problem with gliders is that they are slow, and have poor agility . . .

you may want to check this post
http://www.societyofrobots.com/robotforum/index.php?topic=278.0
Title: Re: water-proofing a servo
Post by: Admin on January 12, 2007, 06:52:09 PM
So I learned just recently that a rubber boot is also often called a rubber bellow. When I google'd it, I found tons of places to buy them . . .

Strangely, hours after I figured that out, someone then emails me with a place to buy rubber boots:
https://buytraxxas.com/product_info.php?products_id=1832

oh well, too late now . . .
Title: Re: water-proofing a servo
Post by: JonHylands on January 22, 2007, 02:45:02 PM
Admin,

Don't know if you've seen this site:

http://www.protacraft.com/

These guys are ROV hobbiests, who decided to build inexpensive parts and sell them.

- Jon
Title: Re: water-proofing a servo
Post by: sotu on April 04, 2007, 06:05:17 AM
I've been thinking about building a submarine robot, but the waterproofing system is allways a challange. I'm looking forward if ure publishing a water proofing turtoriel..!:D
Title: Re: water-proofing a servo
Post by: mhalavo on April 04, 2007, 09:50:42 AM
This might not work for Admin's application but anyone looking into building a seriously waterproof vehicle should concider using magnetic coupling.

This site explains it pretty well:
http://www.dextermag.com/Magnetic-Couplings.aspx?

Most available products are for much larger systems but one could make a simple smaller version on their own for say a propeller.

Here's a crude drawing of a simple setup....
Title: Re: water-proofing a servo
Post by: TravelingPencil on June 10, 2007, 12:59:18 PM
 What about just coating the PCB inside the servo with plasti-dip or better yet something that will cover the electronics with a very thin but waterproof layer of plasti-dip or similar substance without overheating the electronics.

P.S. srry about the late post ;D
Title: Re: water-proofing a servo
Post by: sotu on June 10, 2007, 01:43:51 PM
This doesn't really have anything to do with helping the admin but whatever.
16 servos :o woulden't that cost you ALOT OF CASH$$$? I know servos is more expensive then motors (maybe it depends on the motor/servo) but in norway you can get servos in different strenghts up to 6 Voltage for around 8 dollars (for the 6 V) Personally i only use motors, i find it much easier to just take the bus downtown and buy some motors for my own money then ordering it on the internet and pay the servo and then a bit for the transport (They dont sell servos in Norway, where i live)
Any how, you guys seem smart can u please visit my new topic and help me out?:
http://www.societyofrobots.com/robotforum/index.php?topic=1272.0 (http://www.societyofrobots.com/robotforum/index.php?topic=1272.0)
Title: Re: water-proofing a servo
Post by: paulstreats on June 10, 2007, 05:38:55 PM
hi all,

 Though this doesnt have much to do with the original problem, i did make a waterproof discovery not long ago...

 My electric toothbrush broke a few weeks ago and so i thought id deconstruct it for parts, so when i was doing this i realized that when the toothbrush plugs into the charger section there are no electric contacts from the charger base to the toothbrush itself (obviously for safety around water) and was pleasantly surprised to find parts that are easily available which utilizes the same technology as a usual transformer but where the electromagnetic energy actually passes through plastic from one coil (iron cored from the base) to another coil (in the toothbrush, and also the base coil goes over the core).

 I know this isnt related but it demonstrates how you can completely isolate 1 part of circuitry from another, or also use recharging facilities without posing any dangers. Albeit maybe having to do some convertions of ac/dc to use this type of system effectively.

 Also mhalavo's idea seems quite a good idea, but the magnets should be powerful enough not to become unstuck from each other, not interfere with other electronics, but the magnetism area as a whole is, if researched probably the safest way to proceed for a watery environment.

Title: Re: water-proofing a servo
Post by: Admin on June 11, 2007, 06:51:59 AM
Quote
What about just coating the PCB inside the servo with plasti-dip or better yet something that will cover the electronics with a very thin but waterproof layer of plasti-dip or similar substance without overheating the electronics.
cause I also need to protect the motor :P


As an update, Ive noticed that my oil filled servos are very slowly leaking oil. Im honestly not sure how much oil is left in the servos, but they still work . . . I guess its still not a perfect solution . . . I recently got access to a de-ionized water (does not short circuits or cause rusting) pipeline in the lab, so I might just cheat and not bother with waterproofing anymore . . .
Title: Re: water-proofing a servo
Post by: TravelingPencil on June 11, 2007, 12:43:34 PM
Quote
cause I also need to protect the motor :P
couldn't you cover the holes in the motor with tape to keep the plasti dip out of the motor then plasti dip the motor case(not the shaft or bearing/bushing) with a thin layer of plasti dip then water cool the servo.
Title: Re: water-proofing a servo
Post by: Admin on June 11, 2007, 01:20:21 PM
hmmmmm interesting idea!

it may be a bit hard tho to do because the servos must be reassembled inside the dip . . . ill buy some more servos and try that out . . .
Title: Re: water-proofing a servo
Post by: maverick monk on June 11, 2007, 01:41:41 PM
maby you could put silicon sealent around all the leak pouints in the servo case, and replace the bearings with rubber sealed bearings, then it should stay watterproof, or, do what I do, put a rubber balloon around it, zip tie it off at the shaft and put some hot glue around the end.
Title: Re: water-proofing a servo
Post by: Nyx on June 13, 2007, 08:01:25 PM
If you put the servo in a box with a rubber "nipple", and have a little pump to actually push air into the box... You could keep (too much) water from getting in.
Title: Re: water-proofing a servo
Post by: Admin on June 14, 2007, 04:55:52 AM
This is the mechanical design of what I am doing:
http://www.societyofrobots.com/robottheory/Design_of_a_Biomimetic_Controlled-Curvature_Robotic_Pectoral_Fin.pdf

(on the left of page 5 is a picture of the servo setup)

The problem is that the push rods prevent me from completely sealing off anything. One of my most recent ideas is to cover the entire fin in a glove, but there are issues with that too . . .
Title: Re: water-proofing a servo
Post by: rgcustodio on June 14, 2007, 11:38:44 AM
Just trying to feed in ideas.

Why not remove the electronics and use a waterproof motor or stepper instead? The electronics can be put somewhere safe, or if you're using a stepper all you need is a stepper controller or enough pins from your MCU and long (sufficiently water proofed) cables/wires.

I think this site is worth looking at: http://www.empiremagnetics.com/tech_info_indx.htm (http://www.empiremagnetics.com/tech_info_indx.htm) They have waterproof motors and steppers currently designed for the food industry, etc. Well, they might have something small, as per Admin's size requirements.

(Sorry for not reading the whole thread)
Title: Re: water-proofing a servo
Post by: Admin on June 14, 2007, 01:45:13 PM
OK ok ok . . . so a lot of you are responding to this post lately without reading everything already discussed . . .

The entire device is really tiny - 4 motors packed into half the size of a fist. It must have high positioning control. And because I will be doing this to 20 motors (not one or two), I will need something easy to do, affordable, and highly reliable.

I think that summarized everything . . .
Title: Re: water-proofing a servo
Post by: Eco19R on June 14, 2007, 10:41:59 PM
 why not feed the output shafts through a sealed ball bearing, - those should be water proof as long as there filled with grease right?
Title: Re: water-proofing a servo
Post by: bobbylox on June 15, 2007, 12:02:21 PM
I want to try the non-conductive oil version- where did you buy the o-rings from?
Title: Re: water-proofing a servo
Post by: Admin on October 08, 2007, 10:54:01 AM
Ive developed a new method to waterproof these darn servos. Its the best method Ive come up with so far . . .

To see pics and a quick description, scroll down 2/3rds of the way:
http://www.societyofrobots.com/actuators_waterproof_servo.shtml

Or just watch the video

[youtube=425,350]UZt7BuiNtc0[/youtube]
Title: Re: water-proofing a servo
Post by: aqua_scummm on November 27, 2007, 07:36:17 PM
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 ;)  Read on...

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!
matt pace
http://matthewpace.blogspot.com
Title: Re: water-proofing a servo
Post by: cooldog on November 29, 2007, 09:26:40 PM
where did you get the o-rings
Title: Re: water-proofing a servo
Post by: richard mackie on December 02, 2007, 06:52:28 PM
In the video he said they were from mcmaster but I used to work at Ace Hardware and we sold them individually.
Title: Re: water-proofing a servo
Post by: cooldog on December 02, 2007, 06:55:11 PM
thanks what size is best
Title: Re: water-proofing a servo
Post by: richard mackie on December 02, 2007, 07:23:37 PM
I don't know, I would just bring it in store with you
Title: Re: water-proofing a servo
Post by: kazzer on June 25, 2008, 07:24:50 AM
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 (http://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.
(http://www.caswellplating.com/models/images/subdriver.jpg)

The servos, radio receiver etc. etc are housed within a Lexan tube, and the push rods and prop shaft run through a  seal (http://www.caswellplating.com/models/images/clip_image002_0003.jpg)
see -  http://www.caswellplating.com/models/propeller.html (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


Title: Re: water-proofing a servo
Post by: Admin on June 27, 2008, 12:18:40 PM
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.
Title: Re: water-proofing a servo
Post by: culturedropout on January 10, 2009, 01:49:42 PM
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?

Title: Re: water-proofing a servo
Post by: nac on January 23, 2009, 01:56:00 PM
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
Title: Re: water-proofing a servo
Post by: Admin on January 31, 2009, 09:40:07 PM
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!

Quote
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.
Title: Re: water-proofing a servo
Post by: hoosier122 on May 25, 2009, 11:41:25 PM
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!  :)

Quote
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.
Title: Re: water-proofing a servo
Post by: Admin on May 29, 2009, 10:33:35 AM
Quote
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.
Title: Re: water-proofing a servo
Post by: Razor Concepts on July 07, 2009, 07:19:46 PM
This guy doesn't just plasti-dip the circuit board... he does the entire servo!
How to Waterproof an RC Servo - RC ADVENTURES (http://www.youtube.com/watch?v=YWncPVO1o7s#ws-lq-lq2-hq-vhq)
Title: Re: water-proofing a servo
Post by: Admin on July 08, 2009, 08:23:44 AM
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 (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 . . .
Title: Re: water-proofing a servo
Post by: Razor Concepts on June 30, 2011, 11:31:03 AM
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 (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.
Title: Re: water-proofing a servo
Post by: NGuggemos on August 07, 2011, 11:19:25 AM
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.