Water proofing small motor

[Zacrifice]

Hey
Well I need to make a small hobby motor water proof!

I already have the design idea for the casing, however I'm stuffed on what would be the best thing to use to water proof the shaft of the motor since it needs to be connected to a small prop that will be used to push water around

Heres a picture of a smaller motor in question

I need it to be safe since it will be going into my aquarium.. and it needs to handle a minimum of 2 foot of water depth but deffinatly no more then 2 1/2 feet!

Anyone have any ideas of how best to do it?

(It needs to be a constantly run seal for it too, the motor will effectively be turning 24/7, just speeding up and slowling down)

 

[jplacson]

you should check out a few hobby shops for their RC boats and submarines... see how they are put together... or buy one of those cheap toy submarines and use the design and o-rings or something Good luck with your project

 

[scuba-punk]

A ceramic or graphite shaft seal should do the trick. you can get them on McMaster-Carr's website.

-Frank

 

[Zacrifice]

Hey Scuba-punk, thanks for that pointer, I went looking through there site and I didn't find anything related to what you had said, I found lots of shaft sleave like things, lots and lots of other strange looking things but nothing that looks like a shaft seal that will keep water out of a container... can you point it out?? (like the name of it or something)

 

[herman]

Don't know what your torque requirements are but would it be possible to use a magnetic coupling like some aqurium filters use and eliminate to need for a shaft seal?

 

[scuba-punk]

The seals that i had in mind can be found at the bottom of page 3240 on McMaster-Carr's website. Looks like they have seals down to 1/8" of an inch. Hope that helps! If you have any other questions, let me know.

-Frank

 

[Zacrifice]

Hey Herman!
I had throught of that, however I have no real idea on how I would accomplish something which seems difficult too me!

If you forward me to information which would tell me how its achived I would be very creatful!

Thanks Scuba-punk, I'll go check it out

 

[herman]

Basically, you take 2 magnets, attaching one to the motor shaft and the other to the "other" shaft. RTV or epoxying them to a gear or pully should do. You encase the motor and it's magnet in some form of non-metalic (plastic) waterproof case with the magnet as close to one edge as possible. The other shaft is placed on the other side of the waterproof case as close as possible to the magnet connected to the motor. The "outside" magnet couples with the "inside" magnet through the plastic case. Have you ever dragged paper clips or pins around a table top while holding a magnet under the table? Same principal. If you don't need much torque, it should be fairly easy to do and a lot simpler than trying to seal a rotating shaft.

 

[Zacrifice]

Hmmm Herman, do could you recommend a book or website that would have more details on it?

Also do you know of any way to perform this while keeping the prop going in the same direction everytime it starts up?

 

[herman]

Sorry I don't have any other info at this time, I will do a web search and see what I can find. The output shaft (driven shaft) will always follow the direction of the driving motor so if you start the motor the same direction every time, then the driven device will always turn the same direction. If you reverse the motor direction, then the driven device will also change direction. By the way, this also has the advantage that if something jams the driven shaft (the one NOT connected directly to the motor), the motor will not stop turning or burn up.