Many Newbies and even Pros might want to understand the motors now powering their models. I hope this info here will be useful. Before we can explain the Brushless Motors, we have to understand the Brushed Motors.


Brushed Motors


For years, the world has been using brushed motors and naturally, that was what we got into our electrics. And usually, more often than not, the brushed motor is 3-pole. The 3 pole brushed motor is usually DELTA wound. Three coils are all in series and battery energy is inserted at two junctions at a time via commutators. One coil gets fully energized at the battery voltage and two coils are energized in series thus getting half energized at each pole. There are 3 segments in the commutator of which two are in contact to the battery and one idle. Two permanent magnets are used and if you study the magnetic force around the circumference, they are not uniform. The weakest point is the gap between the two magnets. This is where the stronger pole is positioned with the two weaker poles on the stronger area of the magnet. Electricity runs to the coils via the copper contacts which is the weak link in the circuit and where energy is lost. Thus a brushless motor is only about 60-70% efficient. The battery polarities are shifted by the commutators. If we can shift polarities outside of the motor, we do not need the commutator but only slip rings. Better, if we can fix the coils and let the magnets rotate,we do not need slip rings either. Efficiency can jump to 90%. Why wasn't it done before? Simply because fast switcing FETS came later. Now, say we can switch poles around three terminals of 3 coils in series(DELTA), when do we shift? in the beginning, a sensor sense a small magnet on the rotating shaft controlling the timing. Later, a small mirror in the shaft reflected light into a phototransistor to shift. Eventually, if we switch slowly and gradually increasing it to full speed, we do not need the sensor. That is what the ESC is doing today? Why three wires? many ask. Well, aren't there 3 segments in the commutator? If you had fixed the rotor, there will be one wire to each segment to which the three coil junctions are connected. Modify the housing with the PM in it to run on one end to a bushing or bearing, keeping one end open where the three wires are coming out. THAT IS YOUR BRUSHLESS MOTOR.

Now, we see multi poles in our brushless motors today and not 3 poles. Most have 12 poles! Well. it is like the radial piston engine. We can have 3 pistons or 12. In our cars with 4 pistons, they do not fire all at the same time. The timing is usually 1-3-4-2, firing one after another. If you put the firing schematic on a clock, you will have a pistion firing at 12 o' clock, 3, 6, and 9 o'clocks.
In electric motors, the poles all "fire" simultaneously. In a 12 pole motor,poles 12, 3, 6, and 9 become North poles, poles 1,4,7,10 become South poles, and poles 2,5,8, and 11 are North poles. If you look at them in a circle, they become N,S,N,S, etc..The permanent magnets around them are also arrange N,S,N,S, etc. So, if you switch slowly, all the poles with an S will align with the N magnets. All the N poles will align with the S magnets. But just when they are there, the poles are shifted, all the magnets will move to the next poles, thus rotating. Switch fast and the motors spins fast! Inrunners is when the magnets are rotating inside the coils and Outrunners is when the magnets are outside. Outrunners can be made to look as inrunners when a second housing is used, enabling the motor to have bearings on both ends of the shaft. So far, we discussed the DELTA wind since that is the the winding of a brushed motor where we started our discussion. What is the Y wind. The Y wind is where all the three coils start at a common junction. We will still have 3 terminals and the ESC will feed a + + - or a - - + on the three terminals. Two coils end up in series with one coil. The pole shift rotates the magnets.

Now, we have been talking 3 pole models all the time, how do we wind it on 12 poles. Well, we still have 3 coils actually except that we do not wind it on one pole but on four poles in series. We still end up with three terminals. It can be 3 poles, 6 poles, 9 poles, 12 poles, all a multiple of 3. There are motors(align) that have only 4 poles. The more poles the higher the torque. Its like having a 12 cylinder radial versus 4. It fires at every position hour(not necessarily at the same time).

Our next discussion will be current and voltage, number of turns and wire thickness. We will discuss battery discharge rates(10C, 20C, etc) and how it relates to your motor current draw.


BK