My PBL Project

Driving Question

Is a low-budget autonomous underwater vehicle possible? If it is, what are it's capabilities, and what would be its limiting factors? Would it be applicable in deep sea cable repair, or even oil extraction?

Abstract

As the world becomes more interconnected through fiber optic cables deep under the sea, we need to have a way to survey the ground and repair cables underwater. Divers can't easily reach these depths, and in the event of a failure, a lost robot is a lot easier to cope with than a lost life. To solve this problem, we created an underwater robot, capable of locomotion through a body of water, and the ability to carry tools underwater. To begin this project, we started by creating a basic frame out of PVC pipes, attaching the motors, which we sealed with wax, and wiring all the motors to the ethernet cable. After that, we assembled the controller by soldering all the components to the board and attaching the ethernet cable. We were now ready for the testing phase, where we found that our robot had a 35 degree pitch due to the placement of the motors. We worked towards solving this problem by adding varying weights to the front of the craft until we had a level robot. In the end, we managed to create an underwater robot that was able to move through the water and dive easily. It also had a magnetic plate attached to it, which gave it the ability to transport small tools through the water to a target. We managed to meet all our design criteria, and hope that our project is a step in the direction of fully autonomous underwater robots capable of repair, recovery, and surveying of the ocean floor. In the future, we also plan to add a wireless camera for monitoring, and add more powerful motors for deeper diving, faster movement, and greater load-bearing capacity.

STEM Connection

This project emphasizes multiple principles of STEM. Science is important in the movement of the robot, as we had to determine how we were going to allow an air-filled craft to submerge easily. We found that rotation from a motor could be converted into horizontal force through the use of a propeller, and energy loss could be limited by creating a strong bond. Science also taught us that reversing the polarity of a motor will reverse the direction, so that would allow us to easily maneuver throughout the body of water. The Buoyancy Principle taught us that the water pushes up on the craft with an equal amount of weight as the water the craft displaces. Once we learned how to equalize pressure underwater, the robot displaced barely any water, so it was much easier to dive. With a larger robot, bigger propellers would be required to compensate for the increased upward force.

Technology is utilized in the motors to allow them to be controlled. Electrical engineering is important in the control aspect of the motors. We used a PCB to control the electrical flow to the motors, which in turn would translate to movement. We also used technology in the autonomous aspect of the robot. 2 Arduinos are used, along with an L293D H-Bridge IC, which allows for a 12v motor to be controlled. Variables include speed and direction. One arduino controls where the robot should move, while the other determines how to get the robot to move that way. For example, one may say "turn right", and the other will interpret this as "move right motor backwards, and left motor forwards", which will be communicated to the H-Bridge IC, which will power the appropriate motors in turn. This allows for simple coding, which is almost like psuedocode.

Engineering is utilized in the overall construction of the robot. We needed a robust frame capable of submerging underwater without easily falling apart. We also needed it to equalize pressure with the environment so that it would be able to dive effectively. We accomplished this by drilling holes in the pipes, which allowed water to flow into the pipes, equalizing pressure. When the robot is removed from the water, the holes also help with drainage. With this modification, we are not able to theoretically dive hundreds of feet down (with a longer tether of course).

Math was utilized to balance the robot. Initially, the robot had too much weight in the back, which resulted in a 30 degree upward angle of the craft. This prevented the craft from moving at it's maximum speed, as the force from the motors was focused upward, rather than forward. We corrected the balance by attaching a 3.8 ounce magnetic plate to the front of the vehicle, about an inch away from the end of the netting.

Purpose

In areas where divers can’t access, robots are the only option for surveying and repairing infrastructure underwater. With this kind of robot, companies will be able to survey areas without having to worry about the consequences of a catastrophic failure. The robot is made of cheap materials, so it is relatively disposable, especially compared to their more expensive counterparts.

Expected Outcomes

We plan on creating an underwater robot capable of movement in water, and with the ability to dive. We also plan on adding the ability to carry or use tools, in an attempt to either aid a human, or maintain something by itself.

Materials

1. PVC Pipes

2. Toilet sealing wax

3. Motors

4. Ethernet cable

5. Wire strippers

6. Soldering Iron

7. Solder

8. Drill

9. PVC Elbows

10. Super Glue

11. Fan blades (for motors)

12. Momentary Switches

13. Fuse

14. Buttons

15. Ethernet Port

16. PCB

17. 12 Volt Battery

18. Film Container

19. Multimeter

20. Zipties

21. Power cable

22. Fuse slot

When did we work on this?

We met every Tuesday afterschool to research more about NURC and the different types of robots we could build. We also arranged times to meet at each other’s houses to work on the project and do more research.

Procedure

1. Cut the PVC pipes to their appropriate lengths, and assemble the basic frame with the PVC elbows.

2. Drill holes on the rear supports to mount the motors to.

3. Take the Ethernet cable and remove the outer insulation to reveal 8 wires, 4 white and a solid color, and 4 full solid color. Attach 3 of the solid color wires to the positive terminals on the motors, and solder them on. Cut off the remaining solid color wire.

4. Attach the remaining white and colored wires to their appropriate motors. For example, if you attached the orange wire to the positive terminal, attach the orange and white wire to the negative terminal. Do this with all the wires, and cut off the remaining wire. Make sure to constantly test the connections with the multimeter.

5. Waterproof the motors by covering the holes with paper, then covering in the toilet wax. Poke a hole in the bottom of the film container, then insert the wax covered motor into the container so that the shaft is ticking out of the bottom. Poke another hole in the cap for the wires to run through, then close the container. Make sure that there is no air in it. It should be completely filled with fax. Repeat this with the 2 other motors

6. To attach the motors to the frame, run a ziptie through the mounting holes, and tighten it around the circumference of the motor. Then, use another ziptie to tighten the first ziptie, as shown in the image:

7. Repeat step 6 for the other thruster motor, and simply mount the diving motor vertically as shown in the image:

8. Now that you are finished with the robot itself, you need to move onto the controller. Start by gathering all the items that will be mounted onto the PCB, which includes, the buttons, momentary switches, Ethernet port, fuse, fuse slot, and power cables. Start by soldering the fuse slot into its respective position on the board, as shown in the image:

9. Next, solder the buttons into their slots near the top of the board, as shown in the image: Do this for both buttons.

10. Next, solder both momentary switches into their slots, as shown below:

11. Next, solder on the Ethernet port, as shown below:

12. Next, solder the power cables into their respective red and black slots, and insert the fuse into its slot, as shown below:

13. Then, insert the entire board into the case and seal it shut with the black screws, as shown below:

14. Attach the controllers power cables to the battery terminals, and insert the Ethernet cable into the controller to get started!

Results

We found that a 5.6 ounce magnetic tool tray was the solution to all our problems. Not only did it balance out the robot perfectly, it also doubled as a way to transport tools on our robot, which helped us meet all our design goals.

Discussion

During test operations and display events, we encountered a few issues with the robot. The glue that held the propellors onto the shaft of the motor somehow managed to break its bond, and left the robot with almost no power on it’s left side. Luckily, we managed to reattach the propeller. We also faced a few connection issues on the board itself, but those were also resolved after resoldering everything, along with extensive testing with a multimeter.

Conclusion

In the end, we met all our engineering goals by creating an underwater robot capable of basic movement, including turning, driving, reversing, and diving. We also managed to implement the ability to transport moderately sized metal tools through the water by the use of a magnetic tool tray, which also doubles as a counterweight. We used the plate to correct the 35 degree pitch of the craft, which allowed the robot to stay relatively stable through use.

The robot is controlled by a controller on the surface, which is connected to the robot via a tether. The tether is essentially like a safety line, as in the event of electronic failure, the robot can be pulled back to the surface using the tether. The tether communicates with an on board electronic controller on the robot which drives the 3 motors. One motor controls depth, while the other two control turning and movement. these motors have to be sealed within a plastic case, which is filled with a watertight form of wax. This covers all the openings on the motors and will prevent water from entering and damaging the components. The two pool noodles on top of the robot are used to help stabilize it, as without them, the robot would probably spin out of control when you try to move. We have drilled drainage holes in the pipes to allow pressure within them to be equal underwater. Without them, they would always be filled with air, and the robot wouldn't be able to dive. In the vent of a leak, the water would also be stuck inside the pipes, which would lead to even bigger problems.

Further Suggestions/Real Life Application

In the future, it would be better to create a robot with ballast tanks, as that would allow it to stay underwater without having to constantly hold the dive button. That would also make it more like a real submarine.

Essential Investigation

What if the pool was filled with a more dense substance, like saltwater, or corn syrup?

The buoyancy principle states that the force pushing upwards on the craft is equivalent to the mass of the water diplaced by the object, so a more dense liquid would result in a greater upward force. This would make it more difficult for the robot to dive down, as a greater amount of force would have to be exerted to overcome the opposing force.

What changes would you make for next year?

I didnt consider that putting the chip on maximum load would cause a lot of heat, so I let it run continuosly for too long. The resulting damage was apparent, as the robot became extremely slow. I think that it may have tripped the thermal protection, so the computer forced it to operate at a lower voltage. To fix this, I have added heatsinks to the chips to dissipate heat. I will also add sensors to the robot to create a more intelligent autonomous mode.

What would happen if some insulation came off and caused a short circuit?

A short circuit isn't much of a problem, as water is quite resistive. However, a short circuit would be apparent, as an underwater short circuit would hydrolize the water. This means that it would break water into oxygen and hydrogen, which would create bubbles of gas from the site of the problem. It would also prevent most of the voltage from going to the motor, which would lead to a loss of power.

Would large waves or rough currents be a problem?

While they may hinder movement, failure of the frame is unlikely, due to the robust nature of PVC plastic. If the frame starts to get damaged, we could easily seal all the joints with pipe cement, which would create permanent bonds.

Acknowledgements

We would like to thank Seaperch, and our school for providing us with all the tools and materials we needed to complete our project.