Practicum 1A

The goal of this practicum is to build and test an underwater remotely operated vehicle (ROV).  Using the provided kit, tools, and supplies, you and your partner will build the ROV frame and prepare a waterproofed motor.  Once these items are completed, you will attach a tethered, three motor assembly to your ROV frame.  The tether will connect to a control box, which will enable you to control your ROV in the water tank.  You will then navigate your ROV through a set of hoops and retrieve a loop at the bottom of the tank.  

You have 2.5 hours to meet all of the deliverables of this practicum.  Taking a few minutes to perform a quick read of the entire manual prior to getting started is highly recommended.  In order to finish on time, we recommend that you perform construction tasks in parallel (e.g. frame construction occurring at the same time as thruster assembly) rather than in series (e.g. completing frame construction and then moving on to thruster assembly).  Teamwork and communication are essential to completing this practicum by the end of the session!   

By the end of this practicum session, you and your partner will deliver a Submission Sheet (found on Canvas) to be filled out and uploaded under Assignments on Canvas, and:

2.    Now it is time to wrap tape around the motor.  As shown in Figure 8, tape only a SINGLE layer around the motor so that it will fit into the thruster housing canister with space left for the wax.  Start at one end with the edge of the tape extending about 1/16” (~2 mm) past the end of the motor, so that it can stretch over the end to form a good seal. Pull the tape tightly as you wrap it around the motor.

3.    Ensure that ALL of the holes in the motor are completely sealed by pressing, rubbing, and squeezing the tape over the entire surface of each motor shell.  Your sealed motor should resemble the one shown in Figure 8.

4.    Verify that the sealed motor fits into the thruster housing canister shown in Figure 9 with space remaining around it for the potting wax.

Before drilling the caps and thruster housings, scrape off any plastic lumps that may be in the drilling areas of the parts using your fingernail or a small tool.

1.  Affix the cap on to the thruster housing canister.  Mount the thruster housing canister on the vise so that the cap is facing upwards. BE GENTLE WHEN USING THE VISE - THRUSTER HOUSING MAY BREAK UNDER PRESSURE. If your motor is connected to solid wires, use the smaller 3/32” drill bit to slowly drill a hole through the center of the thruster housing cap, as shown in Figure 9. If your motor is connected to stranded wires, use a 1/8" drill bit to drill a hole through the thruster housing cap. The difference between solid and stranded wires is shown in Figure 10.

2.   Remove the cap from the thruster housing and leave the thruster housing on the vise.  Very carefully drill a 3/32” hole through the center of the thruster housing, as shown in Figure 9. Make sure the drill is held straight so that the hole is NOT on an angle. 

3.    Remove any plastic burrs from the holes that may be left after drilling. Do this by removing the 3/32” drill bit from the drill and passing it slowly by hand straight through the holes, from both directions, a few times, without twisting.

4.    Take the sealed motor that is soldered to two wires.  If the motor is not soldered to two wires, notify a proctor or instructor.  As shown in Figure 11, thread about 2” (5 cm) of the pair of wires through the hole in the thruster housing cap and tie a knot on the inward side of the cap.

5.    Strip about 1/4” (7 mm) of wire coating from the ends of the black and red wires.

1.    Put on a pair of disposable nitrile gloves.

2.    Take the wax that is in your kit and split it into two pieces.  One piece should be about the size of a marble (about 0.5” in diameter).  Save the marble-sized piece for step 6.  Use the remaining piece in step 3.

3.    Roll the remaining piece of wax in your gloved hands for a minute or so until it is softened, as shown in Figure 12(a).

4.    Push and flatten the hand-warmed ball of wax across the end of the motor, about 1/4” thick and the diameter of the motor, as shown in Figure 12(b). 

5.    Insert the wax-coated end of the motor into the thruster housing, until the shaft pokes through the hole in the bottom of the housing, as shown in Figure 12(c).

6.    Press firmly on the back of the motor to slowly move it to the bottom of the housing while the wax in the bottom pushes up around the motor.  Keep pushing until the shaft protrudes from the thruster housing as shown in Figure 12(a).

7.    As shown in Figure 13(b), coil about 1.5” of the two wires below the knot shown in Figure 11 into the end of the housing and press a marble-sized piece of wax on top of the coiled wires to hold them in place.  Next, press the wax down to fill in any remaining space around the sides of the motor. Adjust the amount of wax to fill the remainder of the area at the top of the housing, leaving just enough space for the cap to go on.

8.    Move the lid onto the housing, as shown in Figure 13(c), and press hard to set it into place.

9.    Use a paper towel to wipe all wax residue from the outside of the housing and the motor shaft.

Once the motor is in its thruster housing, ensure that your motor is operational.

1.    Strip the ends of the wires above the cap to prepare them for connection to a power supply.

2.    Test the thrusters with the help of a proctor or instructor.  You will attach the wires to a power supply and apply 6 VDC.  Observe the operation of the thruster motor.  The motor shaft should spin rapidly, indicating that the thruster is good.  The total current draw indicated on the power supply should be less than 400mA, if it isn't then contact an instructor.

3.    If your motor does NOT spin, then try the following:

      a.    Gently twist the motor in both directions by hand, or if it seems stuck, use pliers to turn the shaft, and repeat the test.

      b.    If the motor still does NOT work, inspect the wires for nicks that may have broken a wire. Repair a break by stripping 1/4” of insulation from the ends and splicing them back together (talk to a proctor or instructor about this step and check out the reference page section about extending wires).

        c.    If the thruster still does NOT work, it may have a broken wire inside the thruster housing. The thruster can be opened to see if a wire may have broken away from one of the electrical terminals on the motor. Wax can be removed from the back area of the housing to allow the connection to be repaired, and then the wax and cap can be replaced. If that is NOT the problem and the motor still doesn't work, wax may have entered the motor.  Please see a proctor or instructor if this is the case.

1.    Wipe the shaft of the motor using an alcohol pad to remove excess wax that may have been left over after the potting process, as shown in Figure 14(a). 

2.    As shown in Figure 14(b), use a small piece of sandpaper to roughen the surface of the motor shaft.  This can be done by spinning the shaft against the sandpaper while turning on the thruster using a power supply.

3.    After roughening the motor shaft, wipe it again with a new alcohol pad (NOT the one used to remove wax above). Cleaning the shaft is critical in order for the adhesive to stick to it!  This procedure is shown in Figure 14(c).

4.    Use a vise to hold a threaded coupler, as shown in Figure 15(a). BE GENTLE WHEN USING THE VISE - THE COUPLER MAY BREAK UNDER PRESSURE. Close the vise enough for the coupler to be held tightly without too much compression.

5.    A pair of pliers or wire strippers may be required to get the tee nut started on the threaded coupler, as shown in Figure 15(b).   

6.    Thread the tee nut all the way down the threaded coupler, as shown in Figure 15(c).

7.    As shown in Figure 16(a), the propeller has one side that has a slot.  This side must be placed facing the tee nut.  Place the propeller onto the threaded coupler with the slot side to the tee nut, as shown in Figure 16(b).

8.    Thread a lock nut onto the threaded coupler, as shown in Figure 16(c).

9.    Using pliers or a 3/16" wrench, drive the assembly together by tightening the lock nut. A finished assembly is shown in Figure 17.  Please note that the propeller may not go as far down as the one shown in Figure 17.  If this is the case, have a proctor or instructor check your finished assembly to ensure that it is satisfactory.  

10.   Put on a pair of gloves when working with superglue.  Place a drop of superglue in the hollow end of the shaft coupler and the tip of the motor shaft, as in Figure 18(a) and 18(b), respectively. 

11.   Push the hollow end of the shaft coupler onto the motor shaft, as shown in Figure 18(c).  Your thruster is now complete!

12.   Put your thrusters aside and allow the adhesive to harden, undisturbed, for 10 minutes to reach handling strength. Do NOT apply power to the motor or stress the glued connections until that time has passed.  Notify the instructor or proctor that you have completed this section. 

13.  After the superglue has dried, gently try to twist the propeller on the motor. If it does not turn, check to see if superglue has hardened into the depression of the film canister, sealing the motor shaft to the film canister. If this is the case, use a small flathead screwdriver to pick the superglue off the film canister. Continue until you can turn the propeller.

After completing section 4.6, find a set of three thrusters connected to a 25-foot tether cable to mount in your robot. This 3-motor assembly was included on your tray.  You will mount these thrusters onto your ROV frame.  YOU WILL NOT BE USING THE THRUSTER THAT YOU CONSTRUCTED IN SECTION 4.6 FOR THE REMAINDER OF THIS PRACTICUM.  The thruster that you constructed will be used in future practicums.  By following the procedures in this section, you will mount the motors so that your ROV looks like the one shown in Figure 19.  Note that most of these three thruster assemblies follow this color code: motors with blue tape attach to the left motor, motors with red tape attach to the vertical motor, and motors with green tape attach to the right motor.

1.    As shown in Figure 20(a), thread a large, heavy‐duty zip tie through each pair of thruster mounting holes.  For the two 5” pieces, these holes are at the 1.75” and 3” positions shown in Figure 3.  For the 4.5” piece, the thruster mounting holes are at the 1.625” and 2.875” positions shown in Figure 3.  Thrusters should be mounted on the outside of the frame.   

2.    Place a thruster in the loop formed by each zip tie, and tighten the zip tie around the thruster, as shown in Figures 20(b) and 20(c).  Be sure to mount the vertical thruster with its propeller pointing upward.  The port and starboard thrusters are mounted horizontally and the propellers point towards the nearest end of the ROV.

3.    Install a second heavy‐duty zip tie around the first zip tie, between the thruster and the pipe, at each of the three locations.  Tighten each securely to hold the thrusters in place but not as to squeeze the film canister.  This is shown in Figure 20(c).  Cut off the zip tie tails as flush as possible to avoid leaving sharp ends.

4.    You may use a screwdriver inserted through the angle‐adjustment holes, shown in Figure 21(a), to gently turn the PVC pipes on which the thrusters are mounted.  Adjust the angle of the pipe so that it is oriented in your desired direction.

5.  Use electrical tape to connect a short length of the gray part of the triple motor assembly wire to the frame for strain relief.  This way when you pull on the wire to retrive your robot, the frame takes the pressure and not the small, fragile motor wires.  See Figure 22 for an example.

6.   Attach a retrieval hook from the central table to the bottom of your ROV using three 6” small zip ties, as shown in Figure 21(b).   Find the zip ties on the central table.

7.   Take 1-2 small pieces of pool noodle (available in the tank room) and add them to the front of your ROV, as shown in Figure 23 -- they are cut so that you don't need to tape or ziptie them on. This will offset the weight of the two front-facing side thrusters so that your ROV does not pitch awkwardly forward.

Your final required deliverable is a colored loop located at the bottom of the tank, as shown in Figure 24(a).  You will retrieve this loop using your ROV.  To control your ROV, you will connect the 25-foot tether cable attached to your motors to a white control box, which you will find in the test tank room, as shown in Figure 24(b).  Once the cable is attached to a control box, test each of the thrusters prior to placing your ROV in the tank to verify that they are indeed operating properly.  

Connect your ROV to a control box, test that the box can control your motors, and place your ROV in the tank. The ROV's are typically negatively buoyant because of the motors.  If your robot sinks and the vertical motor cannot move your robot upward, then you need to add extra floats to your ROV since the extra motors add more weight. You will use the control box to navigate your ROV through ONE swim-through hoop, as shown in Figure 24(c).  Your ROV must pass through the hoop. After passing through the hoop, your ROV will pick up the loop using its hook.  You will then return your ROV directly to its initial position. 

Each member of a team must control the ROV, navigate a hoop, and retrieve one loop from the bottom of the tank (be sure to take your selfie with the ROV/loop in the background!).  Submit your team’s loop to a proctor or instructor. 

Disconnect your ROV from the control box, and take your ROV back to lab.  Dry the ROV and thrusters and return the thrusters to central inventory. Use wire cutters to take off the hangers and return them to the proctor or instructor. Remove your front pool noodle and return it to the central table.

Use a permanent marker to write your section number and both teammates’ initials on the shortest horizontal beam through which you drilled holes.  Also write your section number and both teammates’ initials on the motor you built.  Use big letters, you don’t want to lose your robot! Attach your motor to robot frame using a zip tie and store it in one of the designated cabinets in B171 on the shelf labeled with your practicum section number.   

When you store your robot, be sure to store it vertically and not horizontally; vertical storage results in cabinets which look like Figure 25(a) and horizontal storage results in Figure 25(b).  Again, we don’t want you to lose your robots!

Clean up your lab station by stowing all of your tools, picking up any loose parts of your kit, and cleaning up any waste materials like sanded dust or drilled out residue.  Another group of students will be undertaking the lab soon after your section is finished, so please leave the practicum space in the same (or better) condition as you had it when you entered the room today.  Finish filling out your practicum worksheet and submit it on Sakai.

1.    SeaPerch Construction Manual, Hansen, Chris. “SeaPerch Construction Manual – 2011-02S”. SeaPearch.  Office of Naval Research, Feb. 2011.  Web. 10 Jun. 2016. <http://www.seaperch.org/action/document/download?document_id=254> 

2.    SeaPerch Instructional Videos, Hansen, Chris. “Online Training Videos”. SeaPearch.  Office of Naval Research, Feb. 2011.  Web. 10 Jun. 2016. <http://www.seaperch.org/online_training_videos> 

3.    Parts List (Table 1.)