Description

This is the LEGO "fast" motor:

Unlike the slow motor, the fast motor is not as simple to make water-resistant. In fact, this procedure will involve actually taking it apart, which will be difficult to undo if you have second thoughts halfway through. So please make sure you are comfortable with the whole procedure and have all the equipment you need before beginning.


Materials

• Flathead screwdriver
• Needle-nose pliers
• Hot glue gun and glue sticks
• Electrical or duct tape
• Soldering iron and solder
• Wire cutter and stripper
• Pill jar and cap (The ones used in this procedure were obtained from http://www.containerandpackaging.com. The jar is item #J026 (or #J027, whose only difference is its color), and the lid is item #L184, but any of the compatible lids listed will do.)
• Vaseline or any other type of petroleum jelly:
       
• Toilet bowl ring wax:
       
• Hot plate or other appropriate heating device
• Pot or other container for boiling water
• Coffee cup or other container which can withstand the temperature of boiling water

Procedure

1. Remove the Motor from the LEGO Case.
   To open up the motor, we need to remove the bottom, which has a dark grey color. This has to be done carefully, so as not to break it. To begin, insert the screwdriver head into the groove that separates the bottom plate from the rest of the motor case. While pushing on the screwdriver, twist it left and right until the bottom pops open slightly. You can then pry it open a bit more, but not too much, or you may break the plastic.
   
   
   Now, turn the motor to the side and, working from back to front, use the screwdriver to continue prying the bottom plate away from the case. As you do this, you will see some of the little plastic latches that were holding the bottom in place.
   
   
   Repeat the previous step for the other side of the motor and then the front. At some point, the whole bottom should come loose. Simply pull it off, and you will see the actual motor inside the case. Reach in and take the motor out of the case.
        
   
   Using the needle-nose pliers (or just your fingers), pull off the metal contacts and resistor from the back of the motor.
        
   
   Now go to the front of the motor, and carefully pry the LEGO axle up the motor's shaft until it comes off. Don't lose this, since you'll need to put it back on later.
        
   
   
2. Prepare the Front of the Motor
   Now that the motor has been removed from its LEGO case, let's take a look at the new case, which is simply a plastic jar and lid.
   
   
   Before we can put the motor in the jar and screw the cap on, we need to do a bit of preparation. The reason for this is that once we put the motor in its new case, it will be sealed by pouring in hot wax, which we don't want to get inside the motor. So we need to cover all openings. Let's begin with the front of the motor. You should see about three holes.
   
   
   Using electrical or duct tape, carefully cover the holes. There are also some holes on the side near the front, so we'll tape there as well. (Try not to let the tape bunch up - you don't want to add too much to the size of the motor, or it won't fit into the new case.)
        
        
        
   
   
3. Prepare the Back of the Motor
   Now that the front is covered, let's look at the back. Notice that in addition to more holes that need to be sealed, we also have to take care of the two leads sticking out, which will need to be connected by a cord to a power source in order for the motor to work. This is further complicated by the fact that we're screwing a lid onto the back of the case, and so our power cord will have to go through it. So, let's first make a hole in the lid for the cord to go through. Using a 7/64 (or slightly larger) drill bit, make a hole somewhere near the lid's center.
        
   
   Now, we're going to take one of the Mindstorms wires with a block connector at one end and cut it so that it's as long as possible with the block connector at one end and the cut wire at the other. Notice that the cut end is actually two separate wires. Pull them apart (use scissors or a blade if you need to) and use the wire strippers to strip a little bit of the insulation off of each wire.
   
   
   Now take the cut end and pass it through the hole in the jar lid. Carefully solder each exposed wire to one of the leads in the back of the motor.
        
        
   
   Once you're done, your motor should look like this:
   
   
   Now, using the glue gun, carefully fill in the openings at the back and sides of the motor. Try not to let the glue get too thick or the motor won't fit in the new case. And remember, you're only covering the holes to withstand hot liquid wax, which will solidify very quickly. You can also put a dab of glue right on the back where the motor shaft sticks out. Don't worry - it won't make the motor stick.
        
   
   
4. Put the Motor into the New Case
   At this point, the motor is ready to go, but the jar needs one alteration - a hole to allow the motor shaft to come through. Using a 5/32 drill bit, carefully drill a hole in the bottom of the jar, near the center. (The placement doesn't have to be exact.) Reach into the jar and scrape out any loose plastic left over from the drilling.
        
   
   Scoop up a little bit of the petroleum jelly and smear it around the shaft in the front of the motor. This will act as a seal on the motor's front. You can put a pretty decent amount on, but don't overdo it.
        
   
   Carefully place the motor into the jar, pushing the shaft through the hole in the bottom. As you push the motor in, the petroleum jelly will spread out.
        
   
   
   The motor is now comfortably snuggled inside its new case, with its holes plugged and its power cable connected:
   
   
   
5. Secure the Motor with Wax
   To keep the motor in place and provide a barrier to water, we're going to fill in the remaining empty space in the jar with wax. But first we need to get the wax into a liquid form. Set up a hot plate or other appropriate heating device in a safe location. Fill a pot of other heatable container with some water up to about 2 inches high and heat it on the plate until it is just under boiling temperature. (We want it under boiling temperature to minimize bubbles.)
   
   Now get a coffee cup or other small container that can withstand the temperature of boiling water and scoop out some wax into it. (You may need to put a lot of wax in the cup so that it sinks in the water. This is especially true of cups with a lip on the bottom, which will entrap air, causing the cup to potentially tip over.) Put the cup with wax into the water and wait for it to melt fully. (Please note that the reason we need the water is so that the temperature of the wax does not exceed 212 °F. If you were to simply heat the wax in a pot directly on a hot plate, it will likely combust, which you would very much like to avoid.)
        
   
   Once the wax has fully melted, carefully take the cup and pour the wax into the jar all the way to the top. Keeping the jar level, let the wax cool. (If you don't wnat to hold the jar while the wax is cooling, you can take two meter sticks or blocks and place them very close to one another, with a slight crack in between. Rest the jar on them, with the shaft going in between the cracks. There are of course other ways to do this - just make sure nothing pushes on the shaft while the wax is cooling.)
        
   
   Once the wax has cooled, inspect the jar for any serious problems. It's ok if the wax didn't get everywhere. As long as the back of the motor is fully covered and sealed, and there is enough wax to hold the motor in place, then you're fine. Also check the front to make sure your petroleum jelly is still there.
        
   
   If there is anything wrong, you can always pull out the motor, clean it and the jar, and go back to setp 4. Otherwise, simply screw the lid on the jar, put the LEGO axle back on the motor shaft, and you now have a water-resistant fast motor!
        
        
   
   
6. Make the New Motor More "LEGO Friendly"
   There are two problems with the new motor: How do we connect it to other LEGO parts, and how do we align the axle when we want to use the motor to drive a system of gears? To solve the first problem, you can simple hot-glue a flat LEGO piece to the motor. First put the glue onto the LEGO piece and then press the motor onto the glue.
        
        
        
   
   Don't worry too much about centering the motor on the LEGO piece. We'll take care of any misalignments by simply making use of the LEGO universal joint. (Actually, we'll use two.)
   
   
   This piece is particularly useful when you need to change the angle of a rotating shaft. For example, let's say we have our new motor in the following situation:
   
   
   We'd like out motor to connect to the output gear at the opposite corner. Using two universal joints and a connecting shaft, it's a piece of cake.
   
   
   Of course, your situation is more likely to be like the one below, in which you just need to correct a small misalignment. The technique is exactly the same.
        

Done!

You now have a water-resistant fast motor, as well as the means to connect it to your vessel. Though it took a considerable amount of effort, this procedure has the extra benefit that you don't need to limit yourself to the LEGO fast motor. You can actually use any 6-9 Volt DC motor, as long as you get an appropriattely sized jar and can fit the LEGO axle onto the motor shaft.