This is a great, easy project! This project is also a first prize winner in the 2012 Instructables Robot Contest!
This little submersible uses 3 DC motors and a nine-volt battery. It controls the three motors with three buttons. Its frame is built from lego-type pieces. It is very simple and great for beginners, although it does require a soldering iron.
First, using your hot glue gun, glue the propellers to all three of the motors.
Next, take a 9V battery and touch the leads from the motor to the positive and negative terminals of the battery. When you do this, check to feel if the propeller is blowing air. If it is not, reverse the polarity.
Once you have figured out which leads on the motor go to positive or negative, mark them with a + or -.
Now add very long lengths of wire to the leads of the motors you labeled as positive. On the negative side or "ground", solder on a 4-inch length of wire.
Now, hot glue the three motors in place according to the pictures.