There was this another time in early ‘08 that we had a chance to make an aquatic bot for the Techfest at IIT-Bombay. This time one that could move over and under the water surface. It does not look much like a submarine vessel but the important thing is functionality and not appearance. I would approve a dirty looking bot as long as it functions well. The problem statement can be found here in their archives.
We were a much smaller team this time: me, Raghav and Navneet and Naba. We had learnt by this time how to make wireless controllers using the 433 MHz RF modules. The resulting circuits were somewhat complex in wiring because we encoded many states in 4 bits that the RF encoder chip provided, and for decoding we used TTL gate ICs. That involved writing truth tables and making K-Maps. I don't know why I did not put a microcontroller there, that would have made things so many times simpler! Shown below are the transmitter (left) and receiver(right) circuits:
We had the bot made out of PVC pipes and special solvent for the joints. We provided two CPU-fan propellers at the back attached to our own motors kept in wax sealed, greased casing. We had the receiver part kept in a plastic case sealed with M-Seal. Nuts and bolts were attached at all corners so that we could manually adjust the weights on all sides by adding or removing nuts, giving the bot more balance in water. Here is the bot seen from different angles:
You can see a fan in the centre with which we could propel the bot up and down in water. Also seen in the remote control are DPDT switches. There were so many ways we could turn the motors that they took up all 16 states accomodated in 4 bits of the encoder. We tested it in the water tank behind our hostel as always and packed and left for IIT-B that night. I would say that the bot was well received with visitors and organizers. Some battery problems were also there (we used NiMH – hard to charge batteries) that I shall not discuss… they bring out bad memories :(