During my work on my ROV project I considered several ways of waterproofing the motors used as thrusters.
There are many that use bilge pumps as they are already waterproof, but they seem rater bulky and hard to mount.
Others use no waterproofing at all and just run their DC motor straight in the water. That works fine, but you have to clean them thoroughly afterwards.
What I ended up with was to have some custom made ‘stuffing box’s. That is basically a container that is filled with grease in which the propeller shaft runs. This is a good solution but impractical and expensive in some situations.
So now I’m doing some tests using Sugru http://sugru.com/ for waterproofing a geared 12V 1000RPM motor. I applied the Sugru on the motor yesterday and will keep it in a jar of water for the next couple of weeks. Running it (in water) for 10-15 minutes each day. If it still works the plan is to submerge it in salt water at about 5-10m dept for a week or two and see if it still works.
I’ve just started using Sugru and I must say that I love this stuff. I have used Polymorph in the past and will probably use it again if I can’t use Sugru. As a modeling material the Sugru is way better then the Polymorph.
To compare the two I would say;
Pros:
- The Sugru handles as any other modeling clay and you have 30min to one hour to get the shape right. With Polymorph its hot wet and you have to work fast.
- The Sugru comes in many bright colors and you can blend it to any shade by combining colors. Polymorph can be colored, but it’s a pain and you can’t really get the color your after..
- The Sugru bonds to almost anything. Polymorph bonds to almost nothing.
- The Sugru when cured has a rubbery and flex to it, Polymorph is hard and glossy.
- As the Sugru is softer to work with and will fill gaps and give you more detail imprints than Polymorph.
Cons:
- Sugru is expensive compared to Polymorph.
- If you open a 5g package of Sugru you have to use it or throw it away.
- Sugru has limited shelf time before you can’t use it any more. That said, the cured product will last for years.
Well, back to my motor
This is what I did.
As this is a geared motor, the outer shaft isn’t in contact with the inner motor. That makes the gearbox a potential stuffing box. So I opened it up to add more grease as it needs to be completely packed to keep the water out.
Added the cap's as you can't do that later
Added some electrical tape to seal of a big gap in the casing and hold the wires in a loop for stress relief
And started laying on the Sugru
The finished product turned out a bit psychedelic, but I used 5 x 5g packs of Sugru on this motor. It might be too thick, but more is better… right?
And here is the motor submerged in water.
Time will show if this is a way to waterproof motors, or a complete failure :-)
Update 30/09/2011
Just a quick update on my waterproof motor project.
I have had it sitting in a jar of water for 24 days and have found no ill effect. I weight the motor before I started and it has the exact same weight now. That seems to be proof that there has not sipped in any water in these 3+ weeks.
