Small submarines are often called pocket submarines and although the real life ones won't actually fit in your pockets, the one in this Instructable will. It will fit into your pocket and in the water it really does dive and resurface, thanks to different methods of depth control (see step 6 for a movie and step 7 for an additional method).
Above that, it is easy to build from a few components. Apart from the soldering in step 2, which you can do in preparation, you can easily make it in a childrens' workshop. The total cost of materials can be limited to about 6 euros.
This submarine is so simple because of the use of a laminated/moulded solar module, waterproof by itself and by skipping any attempts to waterproof the connections or the motor. Don't worry, many simple electric motors do withstand running them immersed in water. Some of them might corrode somewhat after use, making starting up the next time a little difficult, but For several this will not even be a problem (for hints on which ones see the next step).
"What about the current leaking through the water?" you might ask. This will indeed give a slight energy loss, but it is very limited and the energy comes for free from your solar cells anyway.
I added a short video on March 27th (long video still in step 6):
Step 1: Parts and materials
- low voltage, low current electric motor
- floating material (see below)
- 2 x 15 cm flexible electric wire
- For an optional "periscope" depth control about 1mm diameter steel or brass wire, 10 cm long and piece of clear plastic about 2,5 x 2,5 cm.
Tools and various:
a soldering iron and some solder
hot melt glue gun + glue
waterproof markers to decorate
Here are some specs and hints, but feel free to try out alternatives:
Make sure you use laminated or moulded solar module. Do not use simply encapsulated solar cells. Trying to make the latter waterproof will not solve the problem of condensate and will never reach the level watertightness that comes ready with the laminated/moulded ones
I use a laminated solar module specified as delivering 250mA at 1V, available at Opitec under reference number 103.890 or at Kelvin, number 260190 (at quite a higher price). Using an alternative module delivering 300 mA at 1.5V gives the sub a little more boost for a couple of euros more.
I get very good results with the "FF 130" motor available at Opitec (ref. 224.079). With this motor I left the sub in the pool for a day, took it out a couple days, put it in again and it was still working fine. The more common "RF 300" (851105 at Kelvin) on the other hand seems not to survive repetitive wet and dry conditions. The motor under ref. 851165 at Kelvin also seems to do the trick. It's open structure will also help it dry quickly. The 1.5 mm shaft however will need some tape added arround it to fit common 2mm shaft propellers.
A simple plastic propeller is mounted directly on the motor's shaft. I us the ones available under nr 842.479 at Opitec or 851102 at Kelvin.
The next important thing is the material for the sub's body, giving it its floating capacity. I use 5 to 6 mm thick extruded/expanded polystyrene sheet as found in foam trays, as thermal isolation sold under the name Depron or Climaplan or found under ref. 870.539 at Opitec. It is easy to cut, which is important for trimming your sub. It is rather fragile though, so you will better put your sub in your shirt's pocket, rather than your pants' pocket (the latter is not a good idea with a solar panel anyway).
The amount of material will vary with the type you use and the weight of your other parts. You need it to be able to carry all the other parts, with some floating capacity to spare. Attached is a template scaled to the 6 mm extruded polystyrene sheet (best printed it at 100% by disabling the scale to fit page option when printing from Acrobat Reader). If for example you use a thinner piece of foam tray you should scale to compensate an obtain about same floating capacity. The easiest is to make it to large and cut of the excess material when trimming later.
I have been experimenting with foam rubber and some expanded polyethylene packaging material. This is much less fragile but not stiff enough. You can add (metal wire) stiffeners of course, but that complicates things. Yet another possibility is the use of "Aqua Soft" floating plasticine.