Brushed motor basics

Here's you basic lay out of a rebuildable motor.



Motor Can: The motor can is generally made of steel. It holds the magnets and the bearing/bushing for the pinion end of the armature.

End Bell: This is the end of the motor with. The wires from your ESC connect to it and through the brushes passes the electricity from your battery to your motor. Made of a non-conducting material, on it is mounted the brush hoods, an armature bushing/bearing and sometimes capacitors. In a motor that can be rebuilt, two screws hold the end bell to the motor can.

Brushes:The brushes are what actually pass the power to your motor and makes it go. They're usually made out of a graphite base with copper and silver added for conductivity. Brushes do wear and need to be replaced when discoloured or have reached minimal length (around 7mm or so most of the time)

Exploded view of a motor:

End Bell

The end bell is the end that takes care of the electrical connections to the motor. The wires from your speed controller connect to it and through the brushes passes the electricity from your battery to your motor. Made of a non-conducting material, on it is mounted the brush hoods, an armature bushing/bearing and sometimes capacitors. Generally the end bell is held on by 2 screws, but on certain motors its locked in place by folded over tabs.

Wiring Lugs: This is where your speed control connects to the motor. Each motor is marked a little differently, one of them should have a + sign next to it for the positive wire of your esc. The negative wire connects to the remaining lug.

Brush Spring: The brush springs hold the brushes against the armature allowing electricity to pass from your speed controller to the armature while it turns. Brush springs are easily removed with your fingers by just moving the end of spring out from under the small tab that is on top of the brush hood. You can then just lift it off of the brush spring post to complete the removal.

Brushes: The brushes are what actually pass the battery power to your motor and makes it go. They can be removed and replaced once the brush spring is removed as noted above.

Capacitors: (not pictured) Capacitors are mounted to the motor to help keep radio interference to a minimum. Every electrical motor makes electrical "noise" when they are run. The capacitors absorb this noise so it does no interfere with the operation of your transmitter.

Brush Hood: The brush hoods holds the motor brushes in place on the motor and keeps them in proper alignment with the armature. They also include the wiring lugs for connecting your speed control wires and the mounting post for the brush springs.

Bushing/bearing: The bushing/bearing holds the commutator end of the motor.

Armature

The armature is what spins in the motor and makes you RC vehicle go. Also called the 'Arm'

Electricity flows through the brushes into the commutator, the slotted commutator then passes this electricity into the windings energizing them. Since the windings are wrapped into a coil, they create a magnetic field. This magnetic field is repelled and attracted to the magnets in the can causing the armature to turn.



Armature Stack/laminations: The armature stack is constructed of laminated steel. It holds the windings of the motor and helps increase the magnetic force created by the windings when current is passed through them. Changing the amount of laminations to add or remove material from the stack will change the power band of the motor, it will also effect the efficiency, torque and braking of the motor

Armature Segment: This is often incorrectly called a 'pole' by alot of people (including myself). Brushed motors only have 2 pole (north & south), but they do have multiple segments.

Commutator: Also known 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 (or more) separate pieces and this allows the current to be switched to the different windings on the arm as it spins.
The comm rubs against the brushes as the Arm spin causing friction and wear. Due to this, the comm needs to be cleaned and re-trued by a lathe to ensure consistent running and extend life of you motor.

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

Here's a load of info on brushes for you guys. I've culled this down a bit, back to what is relevant to us as crawlers. But brushes are where you are going to get the most power & torque out of your average machine wound motor that we use. (Some of this stuff is also rules of thumb that I use. There are exceptions to the information that i have left out to make things a bit easier to understand and to not overwhelm with info.)

This is you basic brush:


Brushes are made up of various compounds with graphite being the main component with Copper and silver are added in certain amounts for better conductivity. The graphite in brushes also works as a lubricant for the comm.

On the back of the RC brush is a braided wire, this is the brush shunt. Some people think this is where all the current flows into you motor. ERRRR....WRONG!
The brush shunt is only rated to 10Amps max, the majority of the current is actually transferred to the brush through the brush hood.
There are dual shunt brushes available that increased the current carrying capability of the shunt to 20A (obviously), but they are not worth the hassle in my opinion. Pain in the ass to solder, and more likely to get hung up on the hoods. Many racers used to cut the extra shunt off to make it single shunt again with no ill effects (other than going back to half the current capability of the shunt)

Soldered vs. Bolt on shunts:


There is much debate over which is better, My opinion is that a good solder joint is always more conductive than a mechanical one. But a crappy solder joint will be worse than a bolt on. So if you aren't comfortable soldering brushes on, look for bolt-on brushes, or read on for another slightly dodgy looking option.

If you have good clean brush hoods and eyelets on the brush shunts a bolt on still give a excellent mechanical connection. But dust, dirt and general grime can interfere with this connection causing a drop in power and efficiency. It is also possible due to vibrations for the screw that holds the eyelet on to work loose again causing the same effect. (Not usually an issue with a crawler motor)

Soldered shunts are more secure and safe from vibrating loose and also can flow slightly more current. But it is harder to get a good clean soldered joint without filling the brush shunt with solder or having a 'dry' joint. Soldering dual shunt brushes is a b1tch of a job. It can be done, but it hard to do well. So as i said above, i usually cut one of the shunts off and solder it on like a normal single shunt brush.

If you have brushes without eyelets and don't want to solder them on, you can simply put the shunt under the brush spring tab and use the spring to hold it (pic below). This is OK, but not recommended for producing best power. There's no real side effects for doing it this way other that a slight increase in brush spring tension and looking dodgy

Type of brushes:

There are 4 common types of brushes for RC motor's. The most common two are the Standup (taller than it is wide) and the laydown (wider than it is tall).Laydown and standup brushes are the same size, but they are orientated differently to give to change the way the face contacts the comm (see pic below)
There are also P-94 brushes (almost square, but not quite) and also round brushes (not pictured) that are used by certain manufacturers (Orion, Checkpoint, and peak racing among others)



Standup brushes are your 'everyday brush' used in most Crawler motors as standard. They produce the best low end torque, but don't give best RPM and power can be lacking if you don't choose the right compound.

Laydown brushes are mostly used in stock motors and some mild-wind racing modified. They produce extra rpm and mid-range to top-end power due to overlap. But this benefit comes at the sacrifice of bottom end torque. They are also harder on the comm due to arcing due to this overlap.

P-94 brushes are a propriety brush released by trinity/epic. At the time these were released trinity/epic were claiming up to a 16% increase in power & torque compared to a regular standup or laydown brush, longer brush life and also reduced wear.
Those claims were a lot of marketing hype. But in crawler motors, I've noticed an increase in RPM and overall power (maybe not 16%, but enough to notice), brush life is about the same as a regular brush in the same compound. But wear does increase due to the extra surface riding on the comm.
These also give a very good drag brake due to that extra surface on the comm from the over-sized brush face.

Round brushes were originally released to cut down on wear of the comm and the brush. These are about the same or slightly better than a stand up, but they hardly wear the comm and the brushes last along time (10+ runs in a touring car). This is due to the rounded edge of the brush making a softer 'hit' onto the comm plates than a regular squared brush. This leads to less arcing so less wear. The extra brush life is due to them being able to use a much harder compound than a regular brush.



RC brushes can be broken down into 3 basic compounds. (These are some fairly big generalizations to make it a bit simpler. There are exceptions with certain brushes compared to what I've written below)

High silver brushes produce best power but also generally wear the comm the worst. Brush wear can either be great (brushes lasting for ages) or crap.

High copper brushes produce pretty good power and also have medium wear on the comm. Copper brushes seem to last a very long time, but again this is a rule of thumb. These are exceptions.

High graphite brushes produce lowest power, are very low wear on the comm, but at high voltages & rpm can 'gum up' the comm reducing efficiency and increasing heat.

My personal recommendation is to get a good all round brush. Such as the Reedy 737 (same as the 767), 728 or 729 Quasar (both stand up), the Reedy 767 (more silver) or 766 (same compound as 729) (both laydown) or the Trinity 4380 or 4455 (available in P-94, Standup and laydown) The 4455 is also sold in laydown as the 4500

The best brush to get your hands on in IMO (if you can find them) are Trinity Lemans XXX. These are a very high silver compound but the lubricant package that is used cuts comm wear back to not much more than a copper brush (in my experience anyway). So more power, less wear...Win win!



That covers most of the basics on brushes that is relevant to us.
If you guys have questions about this stuff, make sure you put up a post and i'll answer it.

what colour smoke is best to put in a brushed motor in a crawler?

blacklion wrote:what colour smoke is best to put in a brushed motor in a crawler?

Red is always nice...

BTW everyone...Can we try to keep this stuff on topic, with minimal banter/smart arse comments.
I want to try and keep the threads in here uncluttered and just have tech info for people who want and need it. This is why this sub forum was started in the first place.

If you have a serious question related to a topic, post it up. If its something i haven't covered, start a thread.
But keep it to real tech questions please.