Roaming Robots: Build Your Own Underwater Robot

Abstract

Objective

To build a simple underwater robot.

Credits

Michelle Maranowski, PhD, Science Buddies

• Gorilla is a registered trademark of Gorilla Glue, Inc.
• Elmer's is a registered trademark of Elmer's Products, Inc.

This project is based on the following article from the National Oceanic and Atmospheric Administration: National Oceanic and Atmospheric Administration. (n.d.). Build an underwater robot. Retrieved May 24, 2012, from http://oceanservice.noaa.gov/education/for_fun/BuildUnderwaterRobot.pdf.

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Introduction

The ocean is divided into five zones. These zones go from the surface of the water (0 meters [m]) all the way down to 11,000 m, where there is no longer any light and the pressure of the water can crush a car. Although very little light exists at extreme depths, these deep zones are home to some of the world's most bizarre and fascinating creatures. Animals like viperfish, rat-tailed fish, and giant isopods, shown in Figure 1 below. Scientists can learn a lot by studying these creatures. But the zones where these animals live are very cold and dark, and the pressures are too high for humans to work safely. How do scientists gather information about deep-sea creatures? They rely on underwater robots to do the hard work.

Figure 1. This collection of amazing deep sea creatures includes a (a) viperfish, (b) rat-tailed fish, and (c) giant isopod.

But what are robots and how can they help us? Robots are machines often made to do jobs that are boring, repetitive, or dangerous for humans, like detecting leaks in gas pipelines, or getting rid of landmines. Robots can work in harsh environments, like the ocean or in space, unsafe for humans. An example of a space robot is the Mars Rover. This robot went to the planet Mars to gather information for scientists. An example of an ocean robot is the Tethys underwater robot made by the Monterey Bay Aquarium Research Institute (MBARI). This robot is designed to follow sea organisms while recording the physical and chemical properties of the water around them. Check out this video introduction to the Tethys underwater robot.

This video shows Tethys, an underwater robot that helps scientist at MBARI learn more about the oceans.

There are two kinds of underwater robots: remotely operated vehicles and autonomous underwater vehicles. Remotely operated vehicles (or ROVs) are connected to a cable that allows a human to control the robot from a ship or boat on the ocean surface or from within the robot. Figure 2 below shows a ROV robot. Autonomous underwater vehicles (or AUVs) are controlled by computers on board the robot, and can operate without being connected to the surface. Because both ROV and AUV robots contain computers and electronic equipment, underwater robots need to be waterproof. This means that water cannot damage the equipment because it is inside a covering that prevents water from coming in.

Figure 2. This ROV robot operated by Harbor Branch Oceanographic Institution is 7.2 m long, 3.3 m high and 2.5 m wide and can explore to a depth of more than 900 m. Notice the scientist sitting in the acrylic sphere. (Photo by: National Oceanic and Atmospheric Administration [NOAA])

In this robotics engineering project, you will build an underwater robot, an ROV, that moves up and down using a motor, propeller, and a plastic clothes hanger. Before you start the project, you will need to figure out how and where to test the robot. Will you test it in a swimming pool or in a large container? (Note: Do not test it in a saltwater pool, as this can be dangerous.) If you decide to test the robot in a large container, make sure that the container is deep enough and large enough to hold the clothes hanger. Since the motor is a piece of electrical equipment, you will have to waterproof it by using a balloon to cover the motor and making sure that the edges of the balloon are glued to the surface of the motor. After putting these pieces together, you will have a cool robot that works underwater and is lots of fun to experiment with.

Terms and Concepts

• Robot
• Remotely operated vehicle
• Autonomous underwater vehicle
• Waterproof
• Motor
• Propeller
• Solder
• Buoyant
• Ballast

Questions

• What is a robot?
• What are the differences between an AUV robot and a ROV robot?
• What ways are ROV robots used?
• Why are underwater robots waterproofed?

Bibliography

• Gittings, S. (2006, February 24). Remotely operated vehicles (ROV). National Oceanic and Atmospheric Administration: Ocean Explorer. Retrieved May 17, 2012, from oceanexplorer.noaa.gov/technology/subs/rov/rov.html
• Monterey Bay Aquarium Research Institute. (2010, September 22). Autonomous underwater vehicles. Retrieved May 17, 2012, from www.mbari.org/auv/
• Fraunhofer-Gesellschaft. (2010, November 23). Underwater robots on course to the deep sea. Retrieved June 8, 2012, from http://www.fraunhofer.de/en/press/research-news/2010/11/underwater-robots-on-course-to-the-deep-sea.html

Materials and Equipment

• Motor. 6-12 volt (V) DC hobby motor with sprocket. You can purchase a package of two motors online from Amazon.com.
• Balloon. Use a large heavy-duty balloon (available at a party or balloon store) so that the motor can fit inside without ripping the latex.
• Adult volunteer
• Scissors
• Disposable gloves (pair). Get a pair of gloves that fit your hands but are not too large. You can purchase disposable gloves at a hardware store or pharmacy.
• Gorilla™ super glue. You can purchase Gorilla™ glue online at Amazon.com.
• Silicone adhesive. You can purchase silicone adhesive from a hardware store or online from Amazon.com.
• Rubber bands (2)
• Clothes hanger, plastic. Choose a smaller hanger for child-sized clothes. Smaller hangers tend to fit better into a variety of testing containers.
• Film canisters with caps, empty (2). You can find film and film canisters at a department store or you can go to a camera store and ask for empty film canisters.
• Duct tape
• Electrical wire, 22 AWG, red, stranded wire (3.5 meters). You can purchase electrical wire online from Amazon.com.
• Electrical wire, 22 AWG, black, stranded wire (3.5 meters). You can purchase electrical wire online from Amazon.com.
• Wire stripper. You can purchase a wire stripper at a hardware store or online from Amazon.com.
• Battery, 9 V. You can purchase a 9 V battery from a hardware or department store.
• Battery clip, 9 V. You can purchase a 9 V battery clip online from Amazon.com.
• Optional: solder. You can purchase solder online from Amazon.com.
• Optional: soldering iron. You can purchase a soldering iron online from Amazon.com.
• Optional: waterproof wire connectors (2). You can purchase waterproof wire connectors online from Amazon.com.
• Electrical tape. You can find electrical tape at a hardware store or online at Amazon.com.
• Model boat propeller. You can purchase a package of two propellers online from Amazon.com.
• Elmer's® epoxy. You can purchase Elmer's® epoxy online at Amazon.com.
• Paper plates (2)
• Disposable plastic spoons (2)
• Large container. This project used a gift wrap storage container sized 43.2 x 25.2 x 84.7 centimeters (cm) for testing. You can purchase this kind of container at a department store or online at Amazon.com.
• Optional: Nails, 3 inch (5)

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Experimental Procedure

Waterproofing the Motor

This section of the project requires help from an adult. While it is not difficult to waterproof the motor, it does require carefully cutting and gluing the balloon around the motor. If you do not glue and cover the motor properly, water can leak into the motor through the shaft, which can damage the motor.

1. Figure 3 below shows a motor and a balloon. Notice the size of the balloon; it is large enough to contain the entire motor.

Figure 3. Balloon and motor. The balloon is large enough to hold the entire motor.

2. Carefully stretch the balloon end to end and side to side, to make it more pliable.
3. Holding the motor in the palm of one hand, insert your first two fingers from both hands into the collar of the balloon and stretch it open.
   1. If you find it difficult to insert the motor into the balloon on your own, ask your volunteer to stretch open the balloon while you insert the motor.
   2. When the balloon's collar is opened wide enough, carefully insert the motor into the neck of the balloon, bottom end first, making sure that the motor's shaft is poking out of the collar of the balloon. Also make sure that the motor wires come up from the bottom end, run along the side of the motor, and poke out of the top along with the shaft.
   3. Be extra careful not to tear or shred the balloon as you insert the motor.
   4. The shaft, as shown in Figure 3 above, is the cylinder-shaped pole sticking up from the top surface of the motor. As shown in Figure 3, a white sprocket comes attached to the shaft. The shaft rotates when the motor is connected to power or a battery.
   5. The neck of the balloon should fit tightly around the motor but the motor should be completely inside of the balloon. See Figure 4 below.

Figure 4. Insert the motor completely inside the neck of the balloon with the wires coming out on the side.

4. Now you will need to glue the neck of the balloon down to the top surface of the motor to make a watertight seal. You must keep the shaft of the motor clear, above the part of the balloon you will glue down to the top surface.
   1. Using the scissors, snip off the excess neck of the balloon. Be careful when you do this. If you cut off too much, you may not have enough balloon to completely cover the surface of the motor. If you do not cut off enough, the balloon will bunch up around the shaft, getting in the way of its movement. You might have to cut more than once to get the right amount of balloon to meet up at the base of the shaft. You might also have to glue some of the balloon edges on top of each other.
   2. Put on the disposable gloves. (The gloves prevent the glue from getting on your fingers.) Use small drops of Gorilla super glue and glue down the edges of the balloon to the motor. Follow the instructions on the glue package to make sure that the glue hardens and cures. See Figure 5 below for an example. Be sure not to get any glue on the motor's shaft.
   3. Wrap some of the excess balloon around the wires and use silicone adhesive to adhere the edges of the balloon around the wires. You can also use a little bit of the silicone adhesive around the edges of the balloon to ensure a watertight seal.

Figure 5. Glue the edges of the balloon carefully to the motor surface to make a watertight seal.

5. Once the glue has dried, gather the extra balloon down around the bottom of the motor. Then tie the rest of the balloon with a rubber band as shown in Figure 6 below.

Figure 6. Tie up the rest of the balloon with a rubber band to keep it out of the way.

Making the Connections to the Motor

1. The motor runs on electricity and must be connected to a battery in order to work.
   1. Connect the motor's wires coming out of the balloon to a 9 V battery.
   2. Because the robot will be going into deep water and the battery needs to be kept out of the water, you will need to use two long pieces of electrical wire, one black and one red, to connect the motor to the battery. The length of the wires depends on where you are testing the robot. If you are testing the robot in a container, the length of the wires should each be about 1 to 1.5 meters (m) long. If you are testing the robot in a pool, the length of the wires should each be about 2 to 3 m long.
2. Use the wire stripper to cut two pieces of electrical wire, equivalent in length, one black and one red.
   1. Use the wire stripper to strip off 1 centimeter (cm) of plastic from both ends of each wire.
3. Strip off 1 cm of the plastic insulation from both ends of the motor's wires with the wire stripper.
4. Twist together the end of the black wire from the motor to one end of the black length of wire and tape them together with a piece of electrical tape. Repeat with the red wire from the motor and the length of red electrical wire.
   Optional: If an adult helper has experience soldering you can ask them to solder the connections, as shown in Figure 7 below, rather than twisting and taping the wires. Cover the soldered area with electrical tape to make it waterproof. Soldering will make the connection permanent and more stable. The unsoldered connections (those twisted and taped) are less stable and may need to be checked and fiddled with if the robot is not working.

Figure 7. Optional soldered connection between the motor's wires and two lengths of electrical wire.

5. Test the connections between the motor and battery.
   1. Attach the battery clip to the 9V battery.
   2. Connect and twist together the bare metal end of the black wire from the motor to the end of the battery clip's black wire. Repeat with the red wires. When the red wire is connected, the motor should turn on and the shaft spin. If the motor does not turn on, this may mean that the connections to the motor may not be stable and you will have to redo them.
   3. Once you are sure that the motor spins properly, disconnect the motor from the battery clip.

Attaching the Propeller to the Motor

1. Gently pull the wires from the motor down and against the motor. Use a rubber band to hold the wires against the motor. This will keep the wires from getting in the way of the propeller.
2. Slip the propeller on the shaft of the motor. If the opening is too small, you may have to make the opening a bit larger with a drill or other tool.
3. Mix the Elmer's epoxy according to the directions on the package, using a paper plate and disposable spoon. Carefully apply a small amount of the mixed epoxy to the propeller opening, then attach the propeller to the motor's shaft.
4. Allow the epoxy to harden for 24 hours and cure completely. Once the epoxy has hardened, the underwater robot is ready to be built.

Building the Underwater Robot

1. Attach the two film canisters to the longest edge of the clothes hanger with a few strips of duct tape, as shown in Figure 8 below. The film canisters act as floats to keep the robot buoyant.

Figure 8. Tape the film canisters to the longest edge of the clothes hanger.

2. Twist the wires to the motor together to make one cable. Twisting the wires will enable the robot to sink more easily and not get entangled in the hanger or the motor.
3. Attach the waterproofed motor to the hook of the clothes hanger, as shown in Figure 9 below, with duct tape. The duct tape should not get in the way of the propeller's movement. Make sure to rotate the propeller to ensure that it does not hit the hanger. If the propeller hits the hanger, then undo the tape and reposition the motor.

Figure 9. Completed underwater robot.

4. You may need to attach one or two nails to the hook of the hanger to act as ballast. Ballast acts as weight and allows 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 your container 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 10 below.
   1. The hanger should float just under the surface of the water. Add a nail to the hook of the hanger to help weigh it down if it does not float just under the surface of the water.

Figure 10. Testing the underwater robot. This robot models an ROV robot, because power is being supplied via a cable out of the water.

3. When the robot is floating, connect the robot to the battery. Connect the red wire from the motor to the red wire from the battery clip and the black wire from the motor to the black wire from the battery clip. Make sure that the bare ends of the wires touch. Does the robot move down? How fast does it move? What happens when the robot is disconnected from the battery? Does it move back up slowly or quickly?
1. Safety tip: Keep your fingers away from the spinning propeller to prevent injury.

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Variations

• Add two more motors to the hanger and have the robot move forward and backward, and then turn, in addition to moving up and down. Do you need to add more ballast or floats? What issues do you have to consider in order to make this possible? Once you add more motors, use a double-pole, double-throw switch (also called a knife switch) to easily reverse the direction of the motor. Figure 11 below shows how to wire a double-pole, double-throw switch to the battery and the motor.

Figure 11. This double-pole, double-throw switch is wired so that with every throw, the direction of the motor is reversed.

• Add tools to the robot that enable it to pick up items from the floor of the test container. For example, you could tie strings with magnets to the hanger to pick up metal objects or an electromagnet so that you can pick up and drop things. You will have to figure out if you need to add floats to the hanger to enable the robot to move upward.
• Research robots frequently carry an on-board camera. Cameras let scientists on land monitor what is going on underwater. Can you attach a video camera to your underwater robot? What additional problems will you have to solve for the video camera to work?

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