Electric racing has gotten to the point that, unless your equipment is fresh, it is hard to beat the competition. This doesn't mean that you need brand new stuff each race; it just means that you have to keep the equipment that you have in top condition to get the most out of it. This holds true for electric motors especially. Your electron-sucking power plant has to be well maintained on a regular basis to ensure that it will produce the tire-squealin' horsepower needed to annihilate the guy pitting next to you.
Difficulty Meter and Tools Required
Below is a basic outline of the steps that need to be taken when tearing down, rebuilding, and slapping back together your electric motor between runs. We are going to assume that you know how to do the actual maintenance such as cutting your commutator, so this article will concentrate on the little details involved in removing, maintaining, and reinstalling your electric motor into your machine. The more often you follow these simple steps, the better your motor will perform, and the longer this higher performance will last before it is time to fork out some cash for another spool of wire with two magnets wrapped around it.
STEP 1
Remove Your Motor From Your Car
The first step in this process is to remove your motor from the chassis and get it ready for the maintenance. Be careful when handling the motor, especially after it has been run, since it could be extremely hot. Use a rag or protective gloves while removing it. Once the motor is out of your car, remove the pinion gear and do some general cleaning. Use a soft bristle brush to dust away any dirt, debris, tire foam, etc. from the exterior of the motor.
STEP 2
Make Timing and Polarity Marks on the Motor Can
Motor cans are polarized, meaning that if you attach the end bell on backwards during reassembly, the motor will spin in the wrong direction. 1. To prevent this from happening, simply mark the motor can as to which side is positive and which side is negative. Reference the polarity marks on the end bell to label your can. You can use a permanent marker to do this, but most motor cleaners will remove permanent marker, so you are better to scribe the marking in with a hobby knife.
You also need to note the timing settings for your particular motor. Some motor cans have a scale to show you the degree of advancement, so you simply need to write the number down. 2. If your motor can does not have markings, scribe a mark into the can with your hobby knife again so you know the settings will be correct. If you don't do this step carefully, you may reassemble the motor with too much timing (more power but less efficiency so you could dump) or not enough timing (less power than the race before).
STEP 3
Disassemble Motor and Remove Shims
Now you are ready to disassemble your motor. Loosen the two end bell screws, rotate the end bell to match the keys within the motor can, and your end bell should pull apart. Remove the armature from the motor can, ensuring that you don't drop or lose any of the motor shims that are on either end on the motor shaft. Carefully remove the motor shims from the shaft of the armature, and keep note of where each shim was located, as this is very important for motor performance. (For more information on centering your armature within your motor can.
STEP 4
Remove Old Brushes, Clean Can and Endbell
1. Remove your old brushes from the end bell.
You are now ready to clean your motor can and end bell. For the most part, you don't need to spray any solvents into your motor can or end bell. 2. Simply wipe the motor parts down with a rag to remove most of the carbon and debris buildup. 3. Check your bearings to see if they are gritty. If they are, you will need to spray the entire motor with motor spray and try to relube them with light oil. If they are still gritty, they need to be replaced. The reason it is recommended that you don't use solvent sprays within your motor unless your bearings are gritty is because the solvent will remove all of the lube from within the bearings and could possibly wash debris into the bearing. If your bearings feel smooth and free, you are generally better off just wiping away any junk within the motor can and end bell with a rag and slapping the sucker back together.
STEP 5
True Commutator and Clean Armature
1. Throw your armature onto the motor lathe, and cut away all of the crusty commutator material. You want to remove as little material as possible, and if you follow these steps frequently, you should be able to reface the commutator within two or three thin passes on the bit. 2. Once you are finished lathing the comm, use a hobby knife to carefully remove any debris from between the poles. Insert the hobby knife into the pole slot in the commutator closest to the windings, and pull through the comm to remove any bits of metal that have been lodged in there. 3. Now you are ready to clean the armature. Use motor spray, and generously douse the armature to remove any carbon buildup. Be very thorough, especially while cleaning around the commutator to remove any bits of metal that the lathe may have left behind.
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Check Your Brushes
Brushes are one of the main determinants of performance out of an electric motor. Brushes wear quickly and need to be replaced often to keep the ponies pumping. When it comes time for a rebuild, check your brushes to see what kind of shape they are in. If they are excessively worn or show any sort of discoloration, they need to be replaced. Basically, if you are cutting the
commutator, you should be replacing the brushes, but if your brushes still look fine after you remove some material from the
commutator, you can run them again. You will still have to re-break them in, since the commutator is now a different diameter than it was before. Keep on eye on your brushes, and replace them when necessary. Always remember that, if you cut the
commutator, you have to break in the brushes again whether you replace them with new ones or are reusing the old ones.
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STEP 6
Reassemble Motor
It is now time to reassemble your motor. Before you do this, check the end bell retaining plate to see if it is bent (due to overtightening your end bell or a collision). If it is bent, remove it from the end bell, and use a hammer to flatten it out against a cement floor or other solid object. Slap that sucker back onto the end bell, and continue the reassembly. Ensure that the armature shims are in the correct spots on the top and bottom of the motor shaft and that they don't fall off while inserting the armature back into the motor can. Check and match the polarity of the motor can to the end bell, and match up the timing marks that you scribed earlier. Once everything is back together and matched up, tighten the end bell retaining screws (be careful not to overtighten, or you may bend the plate again), and double-check the armature endplay to be sure that you installed the shims correctly.
STEP 7
Solder On New Brushes
It is time to install some new brushes. You will first need to tin the end of the brush shunt with solder, but be careful not to use too much, as the brush shunt can "wick" the solder into it and greatly reduce flexibility. Bend the end of the tinned brush shunt, and solder it into the corner of the brush hood. Be quick with the soldering to again prevent the brush shunt from soaking up the solder and preventing it from flexing. Let the brushes cool down slightly from the hot soldering iron, and then slide them into the brush hoods and install the motor springs. As a precautionary measure to ensure you don't get a "hung brush," gently pull back the brush by the shunt, and let the spring snap it back against the commutator. If the movement of the brush is sluggish or bound up in any way, remove the brush from the hood, and determine why the brush can't travel freely through the hood.
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Maintenance Frequency
A common question about electric motors is, "How often should one rebuild?" The simple answer is the more often you rebuild, the better. Constant motor maintenance means that there will not be much maintenance necessary to bring the motor back to optimal performance. For example, if you cut your commutator every battery or two, you will only need to make one or two small passes with the lathe. If you wait for 10 batteries or so, the poor conduction and arcing between the brushes and the commutator will have caused excessive damage, and many more cuts will be necessary. Long periods between rebuilds also mean that performance is progressively getting lower as the 10 batteries are passing through the motor. If you are running low-turn motors in the seven- to 10-turn range, you should be cutting them after every battery pack or two. Higher-turn motors can wait longer, but keep an eye on the commutator for wear, and also use the brushes as indication (as mentioned in the other sidebar to this article).
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STEP 8
Break In New Brushes
Brand new brushes have to be seated against the new diameter of the commutator to provide the best performance, but you don't need to go overboard. Simply run the motor without any load for 30 to 45 seconds on a 3-volt supply. Shake the motor back and forth slightly during the break-in to help remove some of the debris developed during the seating process. Now is also a good time to check the rotation of the motor shaft to ensure you marked and assembled the motor properly. You will look pretty silly on the driver's stand when you grab a handful of throttle and send your car in reverse into the guy behind you once the buzzer sounds. When looking at the bottom of the motor with the output shaft facing you, the shaft should be spinning counterclockwise.
STEP 9
Install Motor in Car
It is time to stuff the motor back where you found it before this article started. Install your pinion gear, and be sure that it lines up with the spur gear. Take some extra time to set your gear mesh, and once you are happy with it, double-check that you tightened both mounting screws securely. Install your heat sinks or any other external peripherals, and solder or connect your motor connections while again being careful to match the polarity.
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Brush Hoods And Alignment
It is always wise to align your brush hoods to ensure that both brushes are making contact with the commutator at a 90-degree angle. There are many hood alignment tools available on the market that work well, and when shopping for one, make sure it is suited for the style of brush your motor uses (for example, standup, lay down, P-94, etc.). Once you have aligned the hoods perfectly, you should solder the hood screw to the hood to prevent it from shifting. This is one of the reasons it is recommended that you solder your brushes onto your motor instead of screwing them with the eyelets. If you attach your brushes to your motor with the screws, you will shift the hood alignment when you remove the brushes.. Aligning the brush hoods, soldering the screw to the hood, and using solder to mount the brushes will prevent shifted brush hoods and help to reduce resistance in this area. |
Race Ready
You are now race ready. These simple steps will keep your electric motor running in top condition all the time. The more maintenance you do to your electric motor, the longer it will last you and the better the performance will be, so don't be afraid to take 10 minutes out of your race day for some simple electric motor wrenching.
