RC Electric Motor and Battery FAQs

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Source- http://www.rcracingusa.net/electricmotor.htm

What are the parts of a motor and what do they do?

Armature: The armature (or arm) is what spins in the motor and makes your car or truck move. It is made up of the commutator, laminations, shaft and winds. Electricity flows through the wires from the ESC to the end bell. It then travels through the brushes to the commutator, and into the windings on the arm. Since the windings are wrapped into a coil, they create a magnetic field when current is passed through them. This magnetic field is repelled and attracted to the magnets in the can causing the arm to turn.

Armature Stack: The stack is constructed of laminated steel. It holds the windings of the motor and helps increase the magnetic force created when current is passed through them. Most modified motors have a solid stack; most stock motors have a slotted stack. The slotted stack allows for higher rpm, the full stack allows for more torque.
Armature Label: Rebuildable Stock motors are labeled so it is easy to tell if this arm was made for this motor. This is for racing purposes to make it easy to examine the motor to make sure it is legal for stock racing. Modified motors do not require a label.

Brush: Made of a silver, copper, or graphite compound and at the end of the shunt wire. They are what makes contact with the commutator and transfer the electric current to the comm.

Brush Hood: These hold the brushes in place and keep them at a perpendicular angle with the commutator. The hood holds will sometimes contain hood springs that keep the brush from vibrating inside the brush hood.

Bushings or Bearings: These are in the can and the hood of the motor. The shaft rests on these. Their sole purpose is to reduce friction. Bushings are made of copper and are found in ROAR legal stock motors and some budget modified motors. Bearings are always found in quality modified motors.

Can: The outer part of the motor. It is usually made of steel or some other metal that can contribute to enhancing the magnetic field. The can contains the magnets. A lot of the newer cans, like the Trinity D4 will allow you to remove the magnets. The can holds the bearing that supports the long end of the shaft.

Commutator: Typically referred to as the Comm. The comm takes current from your brushes, which ride on this part of the arm, and sends it to the windings. The comm is not one solid piece, but is actually made up of 3 separate pieces. This allows the current to be switched to the different windings of the arm as it spins. Because it rubs against the brushes as the arm spins, the comm needs to be cleaned and shaped every few runs. This requires items such as a comm stick (for cleaning off all the carbon deposits on the comm and brushes), a lathe (for 'truing' the comm back to it's original shape), and motor spray (for spraying out all the excess dirt and debris).

Endbell: The part of the motor that consists of the brush hoods and the tabs. The endbell holds the bearing that supports the short end of the shaft.

Laminations: The part of the armature the winds are wrapped around. These are usually about half a millimeter thick, and are stacked on top of each other. The laminations are sometimes shaped to provide a stronger field. They are usually made of iron ferrite.

Magnets: They are found inside the motor can. They provide the opposing force that the armature’s magnetic force pushes against. If you don’t have magnets (or more specifically, an opposing magnetic field) then you don’t have an electric motor.

Shaft: The part of the armature that rests on the bushings or bearings. I will refer to the shaft in two parts. The long end is the part of the shaft where the pinion gear is bolted on. The short end is the part of the shaft which the commutator is attached to.

Shims: These are placed on both ends of the shaft. They reduce any unwanted space between the can/endbell and the ends of the armature. They are usually made of steel or Teflon.

Shunt: This is the braided wire that comes out the end of the brush. Some shunts have eyelets on them so you can screw them onto the brush hoods. Soldering them gives maximum electron flow, and better efficiency.

Springs: These keep the brush in constant contact with the commutator. They are sold in different weights. You can change the motor's performance by adjusting spring tension.

Spring Posts: These are what the springs are wrapped around.

Tabs: There are 2 tabs per side (positive and negative) on the motor. You can use both sets for soldering leads, diodes, capacitors, etc...

Timing Ring: This is used to advance the timing of the motor. In a stock motor, the timing ring is fixed, and cannot be moved. It is also what the endbell screws into to keep it attached to the can.

Windings: Each pole of the arm has copper wire wrapped around it. This lacquer coated wire (the lacquer is for insulation) is what the battery current passes through and creates a magnetic field so the motor will run.

What does the turns mean on a electric motor?
A Turn is number of times the wire inside the motor is wrapped around the armature poles. Stock motors have 27 wraps (or turns) of 22 gauge wire, that is, 22 gauge wire wrapped around the armature poles 27 times. Modified motors can have as low as 5 or 6 turns or as many as 20 to 25.o have more comm wear.

What does single, double, triple, or quadruple mean on a modified motor?
A Single has one thick wire, a Double is a two thinner wires, a Triple has three thinner wires than the Double, a Quad has four thinner wires, and so on. So, an 8 Double will have TWO (Double) thin wires wrapped around the pole 8 times. A 12 Triple will have THREE (Triple) wires wrapped around the pole 12 times, and the 10 Single will have ONE (Single) thick wire wrapped around the pole 10 times.

What are the advantages of a single, double, triple, or quadruple modified motor?
A Single provides harder acceleration (torque), while a Quad will provide a much smoother power band. The 8, 12, 10, 14, or 16 turn motors will provide a lot more rpm than a stock 27 turn (less wire means less weight), but, obviously, the 8 will have the best rpm (typically).

Are there any other differences between a stock and modified motor?
A Stock motor has a set timing and has bushing in the can and the end bell. A modified motor has adjustable timing and has bearings in the can and the end bell.

What is a motor lathe?
A lathe is a machine that cuts away small amounts of the comm to restore it to a trued state. Lathing or cutting the comm can be done many times to return it to an almost new state. Having a comm that is smooth and no grooves from the brushes, helps the brushes make better contact.

Are the different kinds of lathes?
Yes, there are lathes that are for non-rebuildable (closed end bell) motors and lathes for rebuildable stock and modified motors. There are also two different kinds of bits for a lathe. A Carbide bit usually comes stock with a lathe. A carbide bit doesn't last as long a diamond bit. A Diamond bit is usually a upgrade and with proper care they should last for the duration of your racing career. Diamond bits cut the comm more accurately than a carbide bit.

What tools do I need to clean a motor?
A comm stick, motor spray, soldering iron, solder, small point Philips screwdriver, cotton swabs, bushing or bearing oil, comm drops, hobby knife, rag and possibly new brushes. If you are really lucky a motor lathe or a friend that can true the comm for you.

What is the best way to clean you motor?
Cleaning your motor can be easy by following these few simple steps.

Step #1 - Remove the motor from you vehicle.

Step #2 - Remove the springs. Note which color of spring is located on the positive (+) side of the motor. The positive side marked with a small + sign on the top of the end bell.

Step #3 - Slide the brushes out of the brush hood. If you are going to have your armature lathed then skip to step #5

Step #4 - Insert the comm stick into the slot where a brushes go in the brush hood. Give the motor a few spins in one direction and then repeat going the opposite. You can attach a pinion gear to the end to help you.

Step #5 - Unscrew the end bell from the can. Note is this is a modified motor make sure you mark the timing and position of the end bell with the can.

Step #6 - Clean the inside of the end bell with motor. Make sure there are no motor shims inside before you clean the end bell. Note: If you are planning on using the same brushes again do not get motor spray on them. Motor spray robs brushes of there lubrication.

Step #7 - Remove the armature from the can and place it aside. Note the location of a shims and washers.

Step #8 - Clean the motor can. You can use motor spray, but it is not recommended that it be sprayed on the magnets. The motor spray can eat away at the glue that holds the magnets in the can. Use a mild soap with water to clean the inside.

Step #9 - Use a cotton swab to make sure no dirt is in the bushing or bearing especially where the arm goes through. A little motor spray applied to the tip of the swab helps get rid of any debris.

Step #10 - Have someone lathe you armature. If you don't have a lathe skip to step #11. Make sure the gaps in the comm are free of any extra copper. You can do this by running a hobby knife or razor blade through the gaps. Be careful not to scratch or touch the comm.

Step #11 - Spray the armature off with motor spray and place it back in the can and screw the end bell back in place. Remember to shim it the same as before and stock rebuildable motors have a small tab on the end bell that lines up with a notch on the motor can. Screw in the two set screws.

Step #12 - Replace the brushes if they are short, show discoloration, have chips or signs of excessive wear. If not skip to step #12B. Brushes come with two different kinds of shunts, eyelets or just straight. If is recommend that you solder you brushes to top of the end bell rather than using the eyelets for better electrical contact. If you do decide to solder the brush on, then lightly tin the end of it with solder and attach it to the end bell. If the solder doesn't stick to the end bell, then use light sandpaper to rough up the surface. Make sure that you don't get to much solder on the shunt, because this will make the brush have difficultly moving in the brush hood once the springs are reattached.
Step #12B - To reuse an existing brush clean the brushes with the comm stick to get rid of any glaze or deposits. I recommend protecting you fingers with a rag so the small pieces of fiber glass from the comm stick don't get in your fingers. Don't ever touch the end of the comm stick. Fiberglass hurts and stays in your fingers for along time.

Step #13 - If you have comm drops put a drop on the end of each brush. This help lubricate the brushes and will help the brushes properly seat against the comm. Put the brushes back inside the brush hood.

Step #14 - Reattach the springs. Remember which one goes on the positive (+) side of the end bell.

Step #15 - Apply a few drop of oil to the bushing or bearings.

You are now ready to break in your clean motor!

How do I break in a rebuilt motor?
You will need a 4 cell battery pack and a way to attach it to your motor. Attach the 4 cell pack to you motor. Make sure you note the polarity (+) and (-) on the motor is the same as the battery. The top part of the battery with the nipple is positive (+). Let the motor run for almost a minute or so. I don't recommend spraying motor spray on the comm while it is running, because motor spray is flammable and duh there are sparks being made between the brushes and the comm. Oh and make sure you lubed your bushing or bearing with oil. This will help the arm spin freer in the can.

What are capacitors?
Capacitors? help stop radio noise caused by electric motors that may interfere with your receiver and cause radio glitches. For more information on soldering capacitors see my soldering tips page.

How should I gear my motor?
This depends largely on the type of motor, track layout, track conditions, and the type of driver you are. First need to understand what a gear ratio is. Check out my RC TUNING page for a gear ratio explanation and starting point gearing chart. Before you put down your car on the track. Study the design of the track. To often people gear their cars to the straightway and not the whole track. If the track is full of turns, use a small pinion gear that will give you more acceleration or bottom end speed. The reason behind this is because before your car reached top speed, the next turn would come up and your car would have to slow down again. If the track has many straight and long paths use a larger pinion gear that will give you more top speed acceleration. The reason behind this is because a straight track will give you a longer period for your car to travel at top speed. Just remember the larger the pinion the less bottom end / take off speed you have. Always make sure you are checking to see if the motor is running hot when you take it off the track after three or four minutes. If the motor is hot go to a smaller size pinion. Every motor is different so experiment.
What do the numbers mean on a stock pro motor.

How do I know which motor is the best?
The labels on many stock pro or dyno'ed motors have the following abbreviations: RPM or revolutions per minute, Power or Wattage, Eff or Efficiency and Torq or Torque. The main number to look at would be the Power or Wattage of the motor. This represents the overall power of the motor. A motor that has a better power rating than other motors is most likely to produce faster top speeds and better acceleration. For a Trinity motor a power rating of 130.0W is really good. The Eff on the label is the motors overall efficiency. The higher this number is will result in better run times and cooler, more consistent performance. Torq and RPM are interrelated because usually the lower the RPM the more Torq a motor will have. Even if you have two of the same kind of motor you may have to gear them different depending on there Torq and RPM. For the most part picking a motor with the best power rating and then looking at the other numbers is your best bet.

How do you care for the magnets in the motor can?
The best way to care for you magnets is to avoid overheating your motor. A magnets loose magnetism, but you can slow this process down by finding a gear ratio that doesn't overheat them. Using a small pinion and a larger spur gear will help in keeping your motor cool. So let the motor cool off before you go run the next pack. Avoid trying to cool a motor down to rapidly because there is a possibility of cracking the magnets. Be especially careful when using compressed air cans, because when turned upside down they can actually freeze objects. Also avoid putting to many harsh chemicals on them while cleaning. Many chemicals can eat the glue that adheres the magnets to the can. If you have lots of money to blow then you could also get a magnetizer which gives magnets their life back.

Are there different types of springs and if so what do they do?
Springs come in a variety of different degrees. 90, 115, 135, 150, 180. Each type of spring puts a different tension on the brush. The most common of the springs are the 135 degree and 150 degree springs. The 135 degree springs will give you more RPM, less power, same torque and less comm wear than a 150 degree spring. The 150 degree spring will give you less RPM, more power, same torque, better results overall for stock and modified racing and more comm wear than a 135 degree spring. The 135 degree spring is the most common type of spring used.

What is a shunt wire?
A shunt wire is the wire that is part of a brush that you connect to the motor hood. This wire is made from very thin twisted strings of copper and are usually tin coated. The wires are very thin to make it as flexible as possible. This is done so that when a softer spring is used so it won't stick in the brush hood. Some brushes are even available with two shunt wires for increased power but often cause a disadvantage due to sticking.

What are brushes?
A brush is what makes contact with commutator and conducts electricity to the comm.

Should I use a brush with an eyelet or no eyelet?
If you are just beginning in RC the eyelet is probably the best way to go. The eyelet provides an easy way to change brushes. If you do decide to go with an eyelet type brush make sure is gold plated. This type of eyelet will have the best contact. If you can't make a good solder joint a screwed on eyelet is much better than a screwed on eyelet. When you become a more experienced racer then I would recommend soldering your brushes to the top of the motor hood. Just be careful to not over tin the end of the shunt wire. Try to use a smaller tip soldering iron when soldering your brushes to help not over tinning you shunt wire. Also once you have you brush in place, whether you solder or use the eyelet, make sure that the brush can move freely without sticking in the brush hood holder.

Are brushes made from different compounds?
Brushes are made from three different compounds (Graphite, Copper and Silver) each one has different characteristics depending what type of racing you are going to do.

What types of brushes are recommended for stock and what type are recommend for modified?
A brush made from a silver compound is recommended for stock. Silver Brushes also leave sludge behind that can only be removed by lathing the comm. Silver should be used for competitive racing where the last percentage of power is needed to win. A brush made from a copper compound is recommended for modified. Copper brushes don't leave behind sludge and works best with high RPM motors.

What are the main differences between the three types of brushes?
The graphite brushes are not really recommended for racing. They have the lowest comm wear, lowest brush wear, high lubrication and the lowest power. The copper brushes are recommended for modified racing. They have the medium comm wear, high brush wear, lowest lubrication and medium power. The silver brushes are recommend for stock racing. They have the least amount of resistance. The have the highest comm wear, medium brush wear, medium lubrication and highest power.

Are there different shapes of brushes for stock and modified?
Yes, stock brushes are a laydown brush they are wider than a standup brush. The purpose of the laydown brush is to get maximum wrap around the comm to increase the RPM and are usually thicker than a modified brush. Modified or standup brushes are taller than a laydown brush.

What is timing?
A motor's timing is the position o its brushes relative to its magnets. When brushes are perfectly centered over the magnets, the motor has zero timing. When you rotate the endbell (and the brushes) in the direction in the direction opposite the motor's rotation, the timing is "advanced". When the endbell is rotated beyond the zero-degree mark in the same direction as the motor's rotation, the timing is "retarded".

How is timing measured?
It is meaured by the degrees the brushes have been rotated away from the center position. Most motors come with a lablel that indicates the degrees and calibration marks to show where the timing is set. Eventhough timing refers to the position of the brushes in relation to the magnets, all motors have either a moldeded-in pointer or an endbell screw that measures timing at a "zero point". This is usually aligned exactly between the two mounting screws on the bottom of the motor can.

Can timing be advanced or retarded to far and what are the effects?
Yes, when the timing is advanced to far the amp draw and motor rpm increase, but overall efficiency and torque begins to suffer. When timing is retarded at all, the motor will run slower and hotter (which is why it's never really used!); zero timing is the lowest point at which a motor timing should be set. A good rule of thumb is that motors with 15 of fewer turns are best set with 0 to 15 degrees of advanced timing, and winds of 15 and above work with as high as 20 degrees of advance timing. If you are unsure how much timing to run, set it on the cautious side and run with less timing; your motor will run cooler, and your car will also run longer!


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Balance leads and power leads on a LiPo battery pack.

On a 3S, the balance leads will be common with one ground and one power, but will have two additional leads that are independent of the primary power wires in order to monitor individual cell voltage.

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