Build a Simple Underwater Robot

Waterproofing the Motor

1. Get your motor and packs of Sugru® ready. Sugru is a "self-setting" rubber, meaning you can mold it with your hands initially, but it will harden and solidify in 24 hours.
2. Use the Sugru to completely encase the motor, as shown in Figure 3.
   1. It will probably take you two to three packs of Sugru to completely encase the motor.
   2. Make sure you let the two wires and the motor's shaft stick out from the Sugru, as shown in Figure 3.
   3. Do not tightly pack the Sugru against the motor's shaft, which will prevent it from spinning. As shown in Figure 3, press the Sugru tightly up against the raised circle at the bottom of the motor's shaft, but leave the top of the circle uncovered.
   4. The Sugru takes 24 hours to solidify completely. In the meantime, you can continue to the next section to attach the propeller to your motor. However, do not put the motor underwater yet!

Figure 3. Use Sugru, a rubber that sets in 24 hours, to make a waterproof shell around the DC motor.

Attaching the Propeller

1. Cut several segments of heat-shrink tubing (both small and medium diameter) to roughly the length of the motor's shaft, as shown in Figure 4.

Figure 4. Cut several segments of heat-shrink tubing to the length of the motor's shaft.

2. Slip a small-diameter segment of tubing onto the motor's shaft. Use a hair dryer to shrink-fit the tubing onto the shaft, as shown in Figure 5.

Figure 5. Use a hair dryer to heat-shrink the tubing onto the motor's shaft.

3. Continue to slip segments of heat-shrink tubing onto the motor's shaft, one at a time, as shown in Figure 6.
   1. Use the hair dryer to heat-shrink each new tubing segment before you add another one.
   2. When the small-diameter segments no longer fit onto the shaft, begin using the medium-diameter segments.
   3. Repeat this process until the outer diameter of the heat-shrink tubing is about the same size as the inner diameter of the propeller. This will probably require roughly four to six segments of heat-shrink tubing.

Figure 6. Place additional layers of heat-shrink tubing on the motor's shaft.

4. Glue the propeller to the shaft using Elmer's® epoxy.
   1. Follow the instructions on the container to mix the Elmer's epoxy.
   2. Place a small amount of the epoxy inside the propeller's cylinder, using a toothpick or a plastic spoon.
   3. Carefully insert the propeller onto the motor's shaft, as shown in Figure 7. Be careful not to let any epoxy go all the way down to the base of the motor's shaft — this could prevent it from spinning once the epoxy hardens. Use a paper towel to wipe off extra epoxy if necessary.
   4. Once the propeller is pressed all the way onto the shaft, apply a dab of epoxy to the ends of the propeller to help seal it in place.
5. Put your motor in a safe place and wait a day to continue your experiment. The Sugru and the epoxy both take 24 hours to solidify completely.

Figure 7. Glue the propeller onto the motor's shaft.

Connecting the Motor to the Battery Pack

1. Your robot's motor will be powered by a 2xAA battery pack. This battery pack has red and black wires, just like your motor.
2. In order to increase the range of your robot, you will use two long pieces of wire to connect the motor to the battery pack. The length of these wires will depend on where you plan to test the robot.
   1. If you test the robot in a plastic container, like a storage bin or a trash can, then about 1 meter (m) of wire should be sufficient.
   2. If you test the robot in a much larger area, like a swimming pool, then you should use longer lengths of wire, like 3–5 m, depending on the size of the pool.
3. Use the wire strippers to cut two pieces of wire of the same length, one black and one red.
4. Use the wire strippers to trim 1 centimeter (cm) of insulation from each end of each wire. If you are not familiar with using wire strippers, refer to the Science Buddies Wire Stripping Tutorial.

6. Twist the red and black wires from the motor together with one end of the long pieces of black and red wires, as shown in Figure 8.
   1. Optional: Ask an adult to help you solder these connections to make them stronger.
   2. Carefully and tightly cover the soldered connections in electrical tape to ensure that they are waterproof.

Figure 8. Twist the wires together and cover them with electrical tape after you solder the connections.

7. Repeat step 6 to connect the other ends of the long wires to the battery pack. When you have finished, your motor, wires, and battery pack should look like the ones shown in Figure 9.

Figure 9. Assembled motor, propeller, and battery pack.

8. Finally, take the cover off the battery pack and insert the batteries.
   1. Make sure the battery pack's power switch is in the OFF position before you insert the batteries.
   2. Make sure you insert the batteries facing the correct direction. The "+" marks on the batteries should line up with the "+" marks inside the battery pack.
   3. After inserting the batteries, turn the battery pack to ON. The motor should spin. If the motor does not spin:
      1. Double-check your electrical connections. Make sure none of the wires you twisted together is loose.
      2. Make sure the motor's shaft is not jammed with epoxy or Sugru. Try spinning the propeller by hand to break it loose if it is stuck.

Building the Robot's Body

1. Tightly secure the lids on the film canisters so they do not leak. Then, use duct tape to attach them to the longest edge of the clothes hanger, as shown in Figure 10. The film canisters act as floats to keep the robot buoyant.

Figure 10. Duct-tape the film canisters to the clothes hanger.

2. Twist together the long red and black wires, and use several strips of electrical tape to hold them together along their length. This will help prevent the wires from getting tangled in the propeller or the clothes hanger.
3. Use duct tape to attach the waterproofed motor to the hook of the clothes hanger, as shown in Figure 11.
   1. Make sure the propeller has room to rotate freely. Do not let the propeller touch the clothes hanger or get stuck in the duct tape.

Figure 11. Use duct tape to attach the motor to the hook of the clothes hanger, completing the underwater robot.

4. You may need to attach one or two nails to the hook of the clothes hanger as a ballast, which acts as weight and enables the robot to sink. You will have to experiment with the nails to find out if ballast is required.

Testing the Underwater Robot

1. If you are using a large container to test your robot, fill it to the top with water. If you are using a pool or other body of freshwater, skip to step 2.
2. Place the robot in the water, with the hook of the clothes hanger first. Make sure to keep the battery out of the water. See Figure 12.
   1. The hanger should float just under the surface of the water. Add a nail to the hook of the hanger to act as a ballast and help weigh it down if it does not float just under the water's surface.

Figure 12. Testing the underwater robot. This robot models an ROV robot, because power is being supplied via a cable out of the water.

3. Turn the battery pack's power switch to ON. Does the robot move down? How fast does it move? What happens when you turn the battery pack to OFF? Does the robot move back up slowly or quickly?
   1. Safety tip: Keep your fingers away from the spinning propeller to prevent injury.
4. If your robot moves up instead of down, do not worry. This just means you need to switch the red and black wires to make the propeller spin in the opposite direction.
   1. Take your robot out of the water.
   2. Use your wire strippers to cut the red and black wires at a point close to the 9 V battery pack.
   3. Now, connect the red wire from the battery pack to the long black wire, and the black wire from the battery pack to the long red wire by twisting them together, the same way you did in step 6 of the section.
   4. Wrap the connections in electrical tape.
   5. Test your robot again. The propeller should spin in the opposite direction, enabling your robot to move down.