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.
Step 2: Step 3 Electric Connections
Next you make the connection with solar module. Put the propeller on the motor's shaft provisionally to check it is spinning in the right direction with the solar panel in direct sunlight. If not, reverse wires.
Most laminated/molded solar modules have contacts wit threaded studs and nuts instead of soldering lips. Do not try to solder on them as their coating will make that very difficult. Make an eyelet to the wire and attach it with a washer and a nut (most often included when purchasing the solar module).
Step 3: Making the sub's parts:
You are ready to go and find some sun and water for a dive. However do check the following steps on assembling, trimming and depth control before you leave. Thake your sccissors with you.
Step 4: Some words about the diving water
The water should be more or less clear. Originally I expected the solar energy caught by the solar cells to diminish with the amount of water above it, thus diminishing the down force (dynamic diving) and stabilising the dive at a certain depth. In practice this effect is far to small in clear pool water and the dive goes down all the way to the bottom. Even a test in quite turbid water made the sub dive to the bottom (be it only 40cm deep, but already hard to see). My guess is that if the sight is limited in the water, the sub is quite likely to dive below the level you can see it. So my advice is to keep to reasonably clear water where you can still see the bottom and use the depth control methods explained later. Of course it is also wise to choose a diving water where you can reach the bottom in case your trimming is not correct.
Step 5: On the spot assembling and trimming
Assemble the parts as shown in the picture. Put the sub in the water. Make sure the motor is filled wit water before starting to trim. Either tap on it with any holes in the motor positioned at the top, or if possible place it under a running tap with one of the openings. A little air left in the motor is not that bad, but to much will make you "overtrim" and your sub risks not surfacing anymore once the air finally does escape from the motor when running.
The last picture shows how to trim (I did it in a bucket for convenience). Once the solar panel catches some sun your sub will run, for the moment remaining at the surface. To dive check out the next step. If you accidently "overtrim", having the sub dive/sink even without running forward, you can always add some floating material back again. Glue it with hot melt or a little super glue, or slide it firmly under the "clip" formed by the solar module.
Step 6: Diving and depth control
If under direct sunlight and with the motor completely at the bow side of the slit, the sub still does not dive, carefully remove a little floating material at the bow. Do not remove to much, as your sub should still float to the surface when the motor stops by making shadow over it. This is your first way to control the depth.
If the water is partly in the sun and partly in the shadow you can "automate" the depth control. You use the rudder to make your sub run in a circle, just touching the shadow area. The sub will rise in the shadow and dive in the sun. Trimming the circle to keep it between surface and bottom is a fun challenge. Check out the video.
Step 7: "Advanced" depth control (optional)
Take a piece of thin steel or brass wire, 10 cm or longer. Stick it in the sail as if it where a periscope or antenna. Slide over a slitted piece plastic as shown. Using clear plastic gives a nice result, being almost invisible in the water. You can cut it from blister packaging or from a overhead projector slide.
Now, when diving, the plastic sheet will hit the water surface and as a kind of break level out the sub, making it not going any deeper. You can have it run at periscope depth, or if you put the plastic piece at the top end and carefully trim it by cutting it smaller, you can make the sub run just under the surface. Just under the surface it will cause a ripple and experience just a little less resistance than when going deeper under the surface. Sliding the motor a little back again can and bending the steel wire can also help trim to get the right effect. Just enjoy trying it out.
April 13th 2008: I have added a video showing the good performance of this type of depth control. In this is example it is a slightly different little sub, with a body made of a laminated paper colour drawing and battery powered (as it is used in an indoor pool).