Science Buddies: "Ask an Expert"

I am creating a prototype "sea mobile" made out of PVC pipes. My next step is to find a little motor and propeller. I started looking to buy an inexpensive motor from catalog/hobby web site, and realized (dope slap) that I need something that will work in water. Nothing I've come across says "water proof" motor. I'm stuck because I don't know where I'd find such a thing, or where to look for a small plastic propeller. I'm really excited about the project, but now I'm stuck! Any suggestions?

Consider different designs, lots of differences.

You may not need to worry about a waterproof motor if you can use an ordinary moter in a location away from the water and send the power to the propeller by a belt or angled shaft.

As an exercise, try to design three different methods for every requirement to gain a versitle idea, then pick the best ones.

Robert Reavis

Small motors from household box fans are inexpensive and easy to work with. If you have an old box fan around the house you can scavenge the motor from that.

dason29 wrote:Small motors from household box fans are inexpensive and easy to work with. If you have an old box fan around the house you can scavenge the motor from that.

That's a really good idea! But I don't think that motor reverses, and I'd like my craft to go backwards, too.
I I have some left-over high speed 12V DC Motors from Radio Shack. I wonder if there is some way to pack it into an old plastic film canister and squirt in some kind of foam that would in effect "waterproof" it. The shaft would stick out of an opening in the top cover; but that opening could be a source of letting water in, though.....Being a chemist, do you have any idea what foam could waterproof my motor, but not jam it up or cause it to overheat? Somehow, i feel like I'm trying to reinvent the wheel here. I mean, I find it hard to believe that there isn't a source for small, waterproof motors, like for little kid's submarines, or pool cleaners, or something!

robertreavis wrote:Consider different designs, lots of differences.

You may not need to worry about a waterproof motor if you can use an ordinary moter in a location away from the water and send the power to the propeller by a belt or angled shaft.

As an exercise, try to design three different methods for every requirement to gain a versitle idea, then pick the best ones.

Robert Reavis

Ummmm, that was my first instinct too, but then I decided against it for two reasons: 1) I'm trying to create a sea mobile that could work in the ocean gathering data and such. It would be buffeted by waves, and even if I stuck my motor where it wouldn't get wet for the purposes of this project, it wouldn't really fulfill my design objectives. 2) The sea mobil (if I ever get it past this problem) will function in a tank at my school science fair, where hundreds of kids from middle school will walk by and want to try it out. I can't take the chance that it will get submerged and then not work.

Thank you so much for trying to help and if you have any other ideas, I would really appreciate your reply!

waterdancer,

This is absolutely not my area of expertise, but I did put "waterproof motor" into a search engine. There seem to be a number of waterproof motors for sail as components of boats, though they might be out of your price range. I also found a few discussions on other forums that might give you some ideas:

http://www.instructables.com/answers/Ho ... or-easily/
http://forums.makezine.com/comments.php ... ionID=1714

Amanda

Amanda, you're fantastic!
That's exactly the kind of information I've been hunting for!
Bunches of thanks,
waterdancer

What about using a water pump such as one you might install in your backyard pond or fountain? Instead of a propeller could your mobile be powered by a water jet? These pumps are fairly inexpensive and designed to be water-proof.

Audrey

To followup on a prior post, the submersible pump idea is good. Use it like a jet.

robertreavis wrote:To followup on a prior post, the submersible pump idea is good. Use it like a jet.

YES, I really like the submersible pump concept! ....so I went trolling for the smallest submersible I could buy. However, after I ripped out the pump from a little froggie fountain I bought cheap at Wal Mart ( I gave my mom the frog), I realized the size of the sea mobile would have to triple/ quadruple??? in order to support it. In other words, I was conceiving of a sea mobile frame made of PVC pipes that wouldn't be much bigger than 6" X 18", because I'm trying to display it in a clear plastic tank and have it maneuver about. If I have to build the hull really big to support such a (relatively) heavy motor, then I won't be able to display it in a reasonable size tank, and I think that would loose a lot of the fun of demonstrating it. I think the concept would work great, but it comes at a big sacrifice. Any other ideas?
Trying not to get frustrated....
waterdancer

Hmmm... I don't know the exact design of your sea mobile but is there anyway you could alter the design to make it more buoyant and be able to support the larger motor? Maybe the shape of the hull or adding extra flotation?

Another idea if the mobile is to large would be to use a small kiddy-pool for demonstration (if your school allows). Although, the advantage of using a clear plastic tank to display it would mean people could see how it works under the water better.

Audrey