How do I waterproof?

[zamboniman60]

I am making a submarine robot, but how do I stop water from coming in where the propeller joins with the motor (inside the hull)?

[Admin]

Very good question. I am currently working on a robot fish so I have very similar problems.

First, go here
http://web.mit.edu/seagrant/edu/seaperch/AdvancedROV/AdvancedROV.html
My gf did this when she was a freshman at MIT, so she told me all about this thing. Click on the thrusters link, it tells you step by step how to do it. However just be aware that motors need cool air to cool down or they will overheat and burnout - sealing a motor in a container would stop this cooling down. So consider some type of heat sinking or just run your motors below the rated voltage.

You may also be interested in this:
http://ocw.mit.edu/OcwWeb/Ocean-Engineering/13-49Fall-2004/LectureNotes/index.htm
Its basically theory of robot subs . . .

And lastly, consider buying a tube of PC11 Epoxy Paste - great for making waterproof seals . . .

[zamboniman60]

2 more questions:

1. can I run water through tubes around my motor for cooling?

2. how can I modify sonar systems for above-ground use for use underwater?

[Admin]

1. You dont need to. Just make heat sinks that wrap around your motor and have good surface area contact with the outercasing - the water your robot is in would cool the outer casing and hence cool your motor. You could also put thermal sensors on your motors and test how much you can run them before they start to overheat.


2.    Hmmmm I am not quite sure how underwater sonar work. Well I understand theory thats simple, but I mean I dont know what the oscillating component is. The circuitry of a land sonar transducer I am sure you can modify for it, but the actual thin film that vibrates to detect and make the sounds I dont think is water proof. Let me know what you find, I am kind of interested too. Considering I make robots for the Navy, I should probably know this . . . 

[zamboniman60]

I'm thinking that I'll make a half-sphere out of resin and put the sonar in that, then modify the circuit a bit.

[Admin]

hmmmm how do you plan to have the sonar sounds pass through the resin sphere and not bounce back?

in about a week or two from now im going to run tests on the Sharp IR ( http://www.societyofrobots.com/sensors_sharpirrange.shtml ) and see how well it works underwater. ill post how well it worked by the end of the month.

[zamboniman60]

Thanks, I think that I can use the sonar with the resin as long as the receiver membrane is physically connected to it...

Btw, this sucker's going in murky water, so the IR's a no-go

[sainathgupta]

wow ,  a really enlightning thread here !

[Admin]

Oh I forgot to post it . . . I was able to use a Sharp IR passing through glass and water of a fish tank to measure the distance of an object moving inside. It worked fairly well at a distance of 2 feet. Just make sure the glass is really clean.

[Tsukubadaisei]

Here is some interesting links (in Japansese, so if you can't understand, use some translator like Babelfish)

http://underwater.iis.u-tokyo.ac.jp/                  (has an English version)
http://www.naoe.eng.osaka-u.ac.jp/ikarobot/
http://www.brain.kyutech.ac.jp/~ishii/              (It is in English)
http://www3.ocn.ne.jp/~nodak/index.html       (not very good)

[Sergius]

Im curious. on the primary page, did the servos that were waterproofed useing the mineral oil make little sound?
this would make sence as all the mechanics are submerged.

[gamefreak]

I'd go with the hydrophone instructions that Admin posted, but is it just me or is that just a normal microphone? and then wouldnt thta move in the canister and cause some noise?

[Brandon121233]

I don't want to sound stupid for pointing this out but I'm pretty sure underwater sonar is very different from that which is used in regular air. Especially the rate at which you can send out pings.

I'm thinking that I'll make a half-sphere out of resin and put the sonar in that, then modify the circuit a bit.

This could also be potentially very difficult to implement since you would have to account for the fact that sound travels at different speeds in different mediums (like fresh water, salt water, air, resin) it would be better to stick with a sonar system meant to be used in water. Like this http://www.garmin.com/products/gpsmap178c/, if this has nothing to do with what you guys are talking about, or you realize the above-then sorry for barging into the conversation.