Roaming Robots: Build Your Own Underwater Robot
AbstractThe world's oceans are home to the most strange and amazing creatures. What do scientists know about these deep-sea animals and how can they study them easily? One way to learn about these animals in their homes is to use underwater robots. Underwater robots can record data that would be difficult for humans to gather. But what are robots and how are they made? In this robotics engineering project, you will discover what makes up a simple robot and build and test your own underwater robot.
Michelle Maranowski, PhD, Science Buddies
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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.
To build a simple underwater robot.
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. 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.
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 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 (you can learn more about electricity from the Science Buddies Electricity, Magnetism, & Electromagnetism Tutorial). 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
- Remotely operated vehicle
- Autonomous underwater vehicle
- 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?
- NOAA Office of Coast Survey (n.d.). Remotely operated vehicles (ROV). Retrieved Feb 20, 2014.
- Monterey Bay Aquarium Research Institute. (2010, September 22). Autonomous underwater vehicles. Retrieved May 17, 2012.
- Fraunhofer-Gesellschaft. (2010, November 23). Underwater robots on course to the deep sea. Retrieved June 8, 2012.
Materials and Equipment
- 3 volt DC motor, available from Jameco Electronics
- 2xAA battery holder, available from Jameco Electronics
- AA batteries (2), available from Jameco Electronics
- Hookup wire, 22 AWG stranded black, available from Jameco Electronics.
- Hookup wire, 22 AWG stranded red, available from Jameco Electronics.
- Wire strippers, available from Jameco Electronics.
- Heat shrink tubing, available from Jameco Electronics
- Optional: soldering iron. There are many different soldering irons available from Jameco Electronics. While you can do this project without one, a soldering iron can be a good investment if you plan on doing more electronics projects in the future.
- Optional: lead-free solder, available from Jameco Electronics.
- 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. They are also available from Amazon.com.
- Duct tape
- Sugru self-setting rubber (three 5 gram packs), available 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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Waterproofing the Motor
- 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.
- Use the Sugru to completely encase the motor, as shown in Figure 3.
- It will probably take you two to three packs of Sugru to completely encase the motor.
- Make sure you let the two wires and the motor's shaft stick out from the Sugru, as shown in Figure 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.
- 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
- 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.|
- 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.|
- Continue to slip segments of heat-shrink tubing onto the motor's shaft, one at a time, as shown in Figure 6.
- Use the hair dryer to heat-shrink each new tubing segment before you add another one.
- When the small-diameter segments no longer fit onto the shaft, begin using the medium-diameter segments.
- 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.|
- Glue the propeller to the shaft using Elmer's® epoxy.
- Follow the instructions on the container to mix the Elmer's epoxy.
- Place a small amount of the epoxy inside the propeller's cylinder, using a toothpick or a plastic spoon.
- 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.
- 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.
- 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
- Your robot's motor will be powered by a 2xAA battery pack. This battery pack has red and black wires, just like your motor.
- 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.
- 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.
- 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.
- Use the wire strippers to cut two pieces of wire of the same length, one black and one red.
- 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.
- 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.
- Optional: Ask an adult to help you solder these connections to make them stronger.
- 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.|
- 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.|
- Finally, take the cover off the battery pack and insert the batteries.
- Make sure the battery pack's power switch is in the OFF position before you insert the batteries.
- 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.
- After inserting the batteries, turn the battery pack to ON. The motor should spin. If the motor does not spin:
- Double-check your electrical connections. Make sure none of the wires you twisted together is loose.
- 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
- 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.|
- 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.
- Use duct tape to attach the waterproofed motor to the hook of the clothes hanger, as shown in Figure 11.
- 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.|
- 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
- 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.
- 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.
- 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.|
- 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?
- Safety tip: Keep your fingers away from the spinning propeller to prevent injury.
- 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.
- Take your robot out of the water.
- Use your wire strippers to cut the red and black wires at a point close to the 9 V battery pack.
- 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.
- Wrap the connections in electrical tape.
- Test your robot again. The propeller should spin in the opposite direction, enabling your robot to move down.
Ask an Expert
- 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 13 shows how to wire a double-pole, double-throw switch to the battery and the motor.
|Figure 13. 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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