Procedure1. Test the motors and mark the polarity of the terminals. It is necessary to mark the polarity of the motor terminals, since we will not be able to see the polarity markings on the motor housing once we wrap it in electrical tape. 2. Make a pair of test wires: (these are temporary, and will be disassembled for making your control box in unit 3)
Connect the black wire to the black alligator clip by twisting or screwing it on. (NO SOLDER). b. Repeat with the loose red wire and the red alligator clip. 3. Look carefully to see if the terminals on your motors are pre-marked with polarity (+/-). If so, continue with #3, if not, skip to “Trouble Shooting”. 4. Mark the positive (+) terminal with a red marker (if available). Connect the exposed end of the red (+) wire to the positive (+) motor terminal. 5. Holding on to the motor, connect the alligator clips to the corresponding (+/-) battery terminals and ensure the motor is in good working order. The shaft should spin rapidly counter-clockwise. 6. Repeat steps 3 through 5 with the other 2 motors. If any motor is not working, get a replacement. Motors should spin COUNTER CLOCKWISE. 1. Make sure the negative and/or positive terminals are marked on each motor so that you can tell them apart after covering the motor in tape. If not, go back to the previous step. 2. Completely wrap each motor with electrical tape to seal the holes. See the tips below before you begin! 3. Make sure ALL holes are sealed, and the motor is still thin enough to easily slide into the container (film can). Motor wrapping tips: The purpose of wrapping the motors is to keep the molten wax out of the motor when we waterproof it, so EVERY hole must be sealed, and folds in the tape where wax could pass through must be avoided. The care with which this is done will help determine how long your thrusters will last. It may be easiest to cover the ends of the motor first with short pieces of tape, and then wrap longer pieces around the sides. But don’t make it too think by wrapping too much tape around the sides, since the motor still has to be thin enough to fit inside the thruster container (film can), while leaving some room for wax around it. You can push the tape right over the motor terminals so that they punch right through the tape. It is best to avoid putting tape on the motor shaft, as this will reduce the efficiency and possibly stop the motor. Make sure ALL holes are sealed, and the motor is still thin enough to easily slide into the container. 1. Using the 3/32” drill bit, drill a hole in the center of each film can cap. The holes in the caps are where the wires pass through, so high precision is not essential. 2. Now drill a hole in the bottom of each film can (see Figure 13). The holes in the cans are where the motor shafts pass through the cans, and form the shaft seals, so it is VERY IMPORTANT that these holes are drilled extremely carefully. First, pick any plastic lumps off of the center of the can with your fingernail or a screwdriver. Then carefully and slowly drill the hole straight into the very CENTER of the can. Pull the drill straight out to avoid enlarging the hole. 3. You can use one of your motors to polish the hole in the can to the perfect size. Hook the motor up to the battery using the test wires. With the motor spinning, carefully push the motor shaft into the hole you drilled, and hold it there for a few seconds, until the motor spins freely. 4. Check each can to make sure that the hole is drilled exactly in the center, and that a motor fits inside easily. 1. On one end of the tether cable, strip off about 15” (38cm) of the outer sheath, being careful not to nick any of the inner wires. This can most easily be done with an Ethernet cable stripper. If using scissors, use extreme care not to cut the insulation on the inner wires. Using a knife is not recommended. 2. Separate the four twisted pairs in the stripped section, as shown in Figure 15 on the next page. The brown pair is not used, and can be left hanging for now. 3. Thread about 4” (10cm) of twisted pair through the hole in each film cap, and tie a knot INSIDE the cap for strain relief. 4. Strip about 1/4” (7mm) of insulation from the end of each wire, for all 3 pairs. 5. Take a pair of wires with attached cap, and one of your taped motors. Solder one wire onto each of the two terminals on the motor: colored wire to (+), and white wire to (-). Repeat for each motor and tether wire pair.  1. Put a small piece of electrical tape over the hole in the bottom of each of your 3 motor containers (film cans). The tape should be tapped on VERY LIGHTLY, so that it keeps the molten wax (How to melt the wax) from flowing out the hole, but pushes aside easily when the motor shaft pokes through the hole. 2. Using pliers to lift a cup of molten wax, fill one film can with about 1/4” (7mm) of wax, not more! 3. Quickly but carefully place one of your sealed motors in the wax. Wiggle the motor until the shaft pokes through the hole in the bottom of the film can. It may take a little pushing to get the shaft to go through, but DO NOT push so hard that you poke another hole in the can. This happens more easily than you might think, since the plastic softens when heated by the wax. Get the motor in and through the hole quickly, since the wax cools and hardens rapidly when the cold motor touches it (Figure 18D). The wax should push up around the sides of the motor, but should not fill in above the motor. 4. Let the wax cool and harden. One end of your motor is now sealed in the wax, so be careful not to push on the motor shaft and break the seal. In order to mount the propellers on the motor shaft, we use a bushing, since the hole in the propeller is larger than the diameter of the motor shaft. We rely on a “press fit” to hold it all together, but to get it together, we need to round off the hole in the propeller so that the bushing can slip inside, and then the hole in the bushing so that the motor shaft can slip inside. We must also be careful not to push on the motor shaft and the can at the same time, to avoid breaking the wax seal around the motor. Instead, we use a scarp piece of pipe to push on the back of the motor. 1. Wipe all wax off of the motor shaft with a paper towel and rubbing alcohol (if available). 2. The side of the propeller with the groove in it is the side that goes towards the motor. Using the triangular blade of the machinist’s scraper, chamfer the hole in the grooved end of each propeller. A chamfer means scraping just a TINY bit around the top edge of the hole: just enough to round the edge of the hole so the bushing can get started, and slip inside when pushed with a vise. Do not drill out the hole in the propeller so that the bushing can slip in by hand… this is TOO MUCH. If a machinists scraper is not available, chamfering can also be done **carefully** with other types of blades, or with a 5/32” drill bit. 3. Using a vise (or large pliers), SLOWLY push the bushings into the propellers. Be careful that they go in STRAIGHT! If the bushing binds, goes in crooked, or otherwise deforms, you will probably need to get a new bushing. If the bushing does not stay all the way inside the propeller, then you have chamfered too much, and you must get a new propeller. 4. Now chamfer the wide end of each bushing with the machinist’s scraper (or 1/8” drill bit). Scrape just a tiny bit off the edge of the hole so that the motor shaft can be pushed in with the vise. 5. Cut a small piece of PVC pipe that is just long enough (usually about 2” or 5cm) to push on the back of the motor with it sticking out of the can about 1/4” to 1/2” (6 to 12mm). Place the piece of PVC pipe against the back of the motor, being careful not to crush the terminals or wires. 6. Hold the propeller/bushing assembly against the motor shaft. Using a vise, carefully press the propeller/bushing assembly onto the motor shaft. (Figures 19 & 21) Go slowly and make sure it goes on STRAIGHT, since it is very easy to bend the motor shaft! Push the propeller on until there is only about 1/8” (3mm) of the shaft left visible. The farther the propeller is pushed onto the shaft, the less likely it is to come off, but the closer it is to the motor can, the less efficiently it will work. 1. Once all the propellers are attached, place the three thrusters into the potting holder, so that they are standing upright. 2. Push the caps up to the knots in the wires and coil the wires into the cans. Make sure the caps go on well, and then remove again. 3. Put on your SAFETY GLASSES before working with wax. An apron and gloves are recommended, since the wax often squirts out during this step! 4. Using pliers to lift the hot cup of molten wax, fill one film can to the top with wax, creating a positive meniscus. 5. Quickly push the cap onto the can, leaving as little air inside the can as possible. Watch for wax squirting out the hole in the cap! 6. Lift the can and look at it from all sides to find any air pockets. While the wax is still liquid, gently squeeze it around the can to remove any air, and fill in pockets.  Positive Meniscus 1. Once the thrusters have been mounted, follow the wire pairs from the thrusters, to where they meet inside the tether sheath. 2. Take a small piece (about 1” or 2.5cm) of the butyl rubber tape (aka. monkey dung) and press it over the wire pairs and the sheath. 3. Knead and work it in well, so that it seals both around and between the wires and sheath, preventing water from getting into the tether cable. 4. Wrap electrical tape over the Butyl Rubber tape to keep it from sticking to anything. 5. After water proofing the tether, make a loop in the tether and attach to the vehicle frame with tie wraps (aka. Zip ties). This is “strain relief”, intended to prevent any pulling on the tether cable from pulling on the motors. Note: Since butyl rubber tape IS electrically conductive, make sure it DOES NOT touch any exposed wires. If you find that the wires are nicked where you cut the tether cable (exposing the inner copper wire), you must either seal them with electrical tape (if possible), or re-do the wiring for the motors. |
