Information Provided By HPI Racing
Electric Car Maintenance
Motor - The powerplant of an electric car, the electric motor requires proper maintenance to run smoothly and efficiently. Motors have many maintenance-intensive parts; we will deal with each one separately.
otor terms: First, however, we will go over the basic parts of the motor. The can is the metal main body of the motor. The motor magnets are glued to the inside of the can. One bearing (for modified motors) or bushing (for some budget modified or stock motors) is at the end of the motor can, where the motor shaft comes out.
The endbell is the plastic part of the motor that seals the motor and has another bearing or bushing where the other end of the motor shaft sits. The brush hoods hold the brushes on the endbell, and the motor springs hold the brushes against the commutator. The brushes are the only parts of the motor that touch the commutator, and are very important in modified racing. Every brush has a shunt wire, which is how the brush is connected to the brush hood. Solder them on for maximum efficiency, or use screws and eyelets for convenience. Most brushes are available with or without eyelets. Some endbells have heatsinks built into them, and others have inspection holes so you can check the commutator without taking off the brushes. Some endbells have both features. The endbell also has the motor tabs, where the motor wires or connectors are soldered.
The armature sits inside the can. The armature includes the motor shaft and all the stuff that spins inside the motor. The commutator is the copper part of the armature, and is only part that most racers have to worry about. It must be in good condition for good performance and high efficiency. The armature also features copper wire wrapped around laminated stacks of metal that are cut into distinctive shapes called poles. All stock motors have the same number of winds (wraps of wire around each pole), while modified motors have less winds with thicker gauge wire for more power and RPM (Revolutions Per Minute).
Now that the motor terms are out of the way, let's move on to motor maintenance!
Cleaning - You should purchase a can of motor spray (HPI's Nitro Car Cleaner is a good bet) and a set of commutator cleaning sticks. Remove the springs from the endbell, then take out the brushes. Don't lose the springs! Holding the motor with the endbell facing down, spray the commutator from three or four sides (rotate it if you have to). Let the motor spray dry, then insert the square end of the blue or red comm stick and hold it lightly against the commutator. Rotate the motor shaft several times to let the comm cleaning stick do its job. Then do the same thing with the green (polishing) comm stick. Racers should clean the motor after every run, casual hobbyists should do it at least every two or three runs.
We'll cover cleaning the brushes when we get to the section on motor brushes.
Commutator Truing - If you don't race, you should have someone true the commutator of your motor (whether it's a stock or modified motor) every ten to fifteen runs. Ask your hobby shop if they true motors there, or find a racer who is willing to help you. At most, you might be charged $5. This helps the shop or racer cover the cost of the diamond bits on the motor lathe, which often costs $85 or more, on top of the more than $100 it cost for the lathe!
If you are a serious racer, you should have your comm trued at least every four to five runs. The more often, the better. Having more 'shallow' cuts more often is better than just a few 'deep' cuts. After each cut, you should replace the brushes as well, since the commutator has a new profile. Backyard bashers won't have to worry too much about replacing the brushes, but it should be done when the the brushes are noticably worn down.
Truing the commutator and replacing the brushes basically 'refreshes' the motor and makes it run pretty much like new, so it's a highly recommended procedure!
Motor Brushes - The brushes on your motor should be cleaned when you clean the commutator. Use the motor spray to clean the ends of the brushes, and then use the round end of the blue or red comm sticks to clean the face of the brushes. Rotate the sticks, don't move them up an down on the face of the brush! Then use the green comm stick to follow up the cleaning.
About brushes and comm truing: Casual R/C hobbyists won't need to replace the brushes on their motors very often, only when the brush gets worn down to about 2/3 its original length. Using serrated-face (quick break-in) brushes is fine for the 'backyard basher'. Racers, on the other hand, should get a new set of brushes every time they have the commutator trued on their motor. This allows the new brushes to re-seat themselves on the new, smaller comm diameter. The race-style brushes that don't feature a serrated face are best for serious racers, since the serration breaks in quicker, but causes a little extra wear on the commutator that racers may not like.
A note about high silver content motor brushes: If you use a motor that has high silver content, you should know that those brushes should be replaced every two or three runs because they wear very quickly. They are meant for serious racing only! If you are a casual hobbyist and bought a motor that has these brushes in it, you should replace them with an economical pair of brushes when the originals wear out.
If you run your motor in very hot conditions (no cooling air, high gearing, etc.) there is a chance your brushes could be damaged. If the brushes, commutator, endbell or brush springs look discolored after a run, you need to take it easy on the motor, or it won't be able to run much longer! Remove the inner body or use a smaller pinion or larger spur gear when running the car with that motor. Beginners need to be especially careful with modified motors, because the gearing for them must be lower than for stock motors.
Brush Springs - Most R/C hobbyists shouldn't need to ever replace the springs on the motor. If you run the motor very hot (see above) there is a chance you can damage the springs so that they don't maintain the same tension on the brushes. A sure sign you are running the motor too hot is that the brushes come unsoldered! If this happens you will probably have to replace the brushes and springs, as well as true the comm, to get the motor up to normal operating standards.
Bushings and Bearings - Use an oil specifically made for bushings or bearings, and completely fill up the end cavity where the motor shaft sticks out on the outside of the can and endbell. Fill one end of the motor, spin the shaft a little, then fill the other end. Oiling the bushings of a stock motor is very important, since not oiling them can cause extra friction you just don't want!
Batteries - Many racers follow a myth that there is a science to charging and discharging batteries. Here is the simple truth:
Charging - Use a peak-detecting linear charger to charge the batteries at 4 amps. That's it!
Battery chargers that use a timer, or feeling the warmth of the batteries is nowhere as exact as peak charging, but for casual R/C drivers, it gets the job done. The HPI Team Drivers at the ISTC World Cup charged their batteries at 4 to 5 amps.
Discharging - For 95% of racers, all that is needed to discharge the battery after running is to run the car until it is very slow, then take the battery out and let it and the motor cool down.
If you don't have time to run the batteries down (for instance, at organized races where you can't run your car when it's not your race), you can use a single 12 volt automotive light bulb (#1157 standard type bulb) to discharge the battery pack. Some racers feel that using 20 amps to discharge the batteries after a race allows them to gear the car better, but with today's RC2000 and RC1700 batteries runtime is much less of a factor, especially in stock class racing. Modified racing is a slightly different story - you still have to know how to gear the car to avoid dumping.
You can run most battery packs more than once a day, as long as you let it cool down first! Batteries such as 1400's or 1500's shouldn't be run more than once a day very often.
The reality is that it is easy to listen to experienced racers go over the 'proper' way to charge or discharge a battery, but you should know that there is no need to over-analyze the simple process of charging and discharging a battery pack. Properly cared for, a battery pack (even a cheap one) will last you for many years.
