ROVs in a Bucket Building an Underwater Robot. 5.0 Building the Tether

Transcription

1 5.0 A professional ROV is connected to the controller box by strands of wire. The bundle of wires are encased in a single sheath. The connecting wire is called the tether. In our project the tether is constructed of 18 gauge speaker wire. The thrusters are connected to the controller by three 30 strands of paired 18 gauge speaker wire. The wire to the bilge pump cartridges as it comes from the factory is 16 gauge, and is thicker than the speaker wire selected in this project. The 18 gauge was selected because it is less expensive than the 16 gauge and the power loss when the electricity is transmitted through the 30 tether length is acceptable. Cut three thirty foot lengths of the speaker wire. Each one of these strands will connect to one thruster assembly. In addition, cut one ten foot length of wire and put it aside. This shorter length will be used to attach the controller system to a 12v power source. Take one of the bilge pump cartridges and unpack the connecting wires. The ones I use have a brown wire and a black wire. Figure 5.1: The bilge pump cartridge. The very end of the connecting wires sometimes have solder on them. This makes the insulation difficult to strip from the wire. I use the wire cutters to cut this piece off. Then strip 1 ½ of the insulation from each of the wires. Figure 5.2: Stripping the wire ends 33

2 Take three of the 30 strands of speaker wire and hold them so that three of the ends are at the same end point. Hold the strands together and tie a loose knot about two feet from the end. Do the same thing to the opposite end of your tether. This will keep the strands together while completing the wire connections. Figure 5.3: Three pairs of speaker wire make up the tether. Use the wire stripping tool to remove the plastic insulation from each of the wire pairs. Leave about an inch of bare wire at the ends. By using your fingers, twist the bare ends of each wire so that the strands stay together. At this time cut 3 1 pieces of the 3/16 yellow shrink tube and 1 pieces of the 3/16 black shrink tube. Figure 5.4: Strip each end of the speaker wire pairs. Do both sides. Now we ll attach the tether to the thruster wire. In this step its best to be consistent with which color wire goes to which. This will prove helpful later when we test the thruster assembly and make certain that the propellers are all spinning in the same direction. I use the convention Brown to Copper, and Black to Silver. It doesn t matter which is used, as long as it s the same for all three motor assemblies. Now slide a yellow piece of shrink tube over the brown thruster wire. Figure 5.5: Line up one of the copper speaker strands and a brown thruster wire. Hold the wires together so that they cross. Like they do in the picture of Figure 6. Figure 5.6: Cross the wires like so. 34

3 Figure 5.7. Now, using your fingers, twist the strands until they appear as a single wire.. Figure 5.8: Now, bend the twisted wires away from the wire length that you slid your shrink tube onto. Figure 5.9: Slide the shrink tube over the twisted wires so that no bare wires are visible. Now do the same thing and connect the black wire of the motor assembly with the copper speaker wire. Figure At this time you should verify that the silver speaker wire is connected to the brown thruster wire, and the copper wire to the black. With both shrink tubes slid around the twisted, connected wires you re ready to shink the tube. 35

4 Figure Hold the heat gun about an inch from the shrink tube and turn it on. For a moment it will seem like nothing is happening.. then the wrap will shrink and mold itself to the twisted strands of wire. Do this for both the black and yellow shrink tube. The wires are now securely connected. Figure Repeat this procedure for all three of the thrusters. When complete, all three of the thrusters will be connected to the tether. All of the splices will be located at the same distance from the thrusters. Hold the wire above the shrink tube so that the three thrusters are dangling down. By doing this, you ll be able to determine where to put the three 4 cable ties around the splice. Figure Before securing the splice with cable ties, you can tape the spliced wires together using the electrical tape (not the temflex). Start just below the end of the splice and wrap the tape tightly around it at an angle until you ve covered the splice. Figure Get 3 4 cable ties. Put one around all three speaker wires at the lower end of the splice, one in the middle, and another at the upper end of the splice. This will take the stress off of the splice when you re carrying the system out of the water, or when you re tugging on it during retrieval. 36

5 Now its time to secure the tether. The three pairs of speaker wire connected to the thrusters, combined, make up what is termed the tether. These three wires must be tied together to make the tether manageable. Put the thrusters in a position where the tether can be pulled somewhat taught. Pull the other end of the tether and tie it to something so that the three wires are hanging like a clothes line. In this position, put one of the 4 cable ties every foot of so along the tether s length. In a 25 tether, you ll need at least 25 cable ties. More is better. By tying the three strands together the tether will behave like one thick wire. When the ROV is in the water the tether will be more easily managed when it is secured like this. Figure 5.15: Stretching the tether so it can be secured with cable ties every

6 Figure 5.16 & What the tether looks like with cable ties every foot or so. With a cable tie applied every foot, or so, the tether will be easier to transport and operate. 38

7 Figure 5.18: Trimming the plastic cable ties with the flat end of the cutters facing the buckle. Trim the excess ends of the cable ties. Note: put the flush end of the cutters against the point on the cable tie where the end is inserted. By cutting it here, there will be no nub jutting from the cable tie. The nubs can be sharp if the trimming is not done well. Once the tether has been finished in this manner, it can be connected to the switches in the controller jar. 39