All About RC Car Brushless Motors

Source
Havoc 1/10 Spec Brushless System: 21.5
Havoc 1/10 Spec Brushless System: 21.5

This is a great motor. I've owned Novak motors and ESCs and they have never failed me. This one is a good introductory motor, and the price is awesome at Amazon.

 
A brushed motor schematic.
A brushed motor schematic. | Source
A basic schematic of a brushless motor
A basic schematic of a brushless motor | Source

Some background

This is really only relevant to people who are involved in radio controlled cars as a hobby, or who are looking at getting into it. I intend to clear up some of the misconceptions about the brushless motors used in RC cars with extreme prejudice, explain how they differ from standard brushed motors, and general cool stuff about them. But first:

What are they?

Brushless motors are essentially standard motors turned "inside out". That is to say, when normally a brushed motor would have a commutator and a rotor that contacts the commutator ("comm") to transfer current and feed its magnets, a brushless (BL) motor does not. It works by a principle called induction: Immersing a magnet in a changing magnetic field will cause it to move. Thus, this brings up the most interesting fact about BL versus brushed motors:

There is no physical contact between the electrical components at all.

This is important. Without this particular factoid, we would not be able to produce motors that are

  • Efficient
  • Fast
  • Powerful

This is where the "inside-out" bit comes in. You see, brushed motors are essentially a magnetic can with a rotor inside that can change the polarity of its magnetic field in response to changing electrical contacts. In a BL motor, this does not happen. Rather, the permanent magnets are on the rotor ("rotating part"), while the changing magnetic field is supplid by elements in the can, or the stator ("static part"). This lack of direct contact is important. It means far less friction than a standard brushed motor, and less wear on the moving part (not "parts", as only the rotor moves in a BL motor).

The changing field in the stator is supplied by electronic control via the car's ESC (electronic speed control). That's why there are three poles (labelled A, B and C on the can) for providing power: so that the ESC can set the motor's speed by altering how quickly it "moves" the magnetic field. Faster moving = faster spinning rotor

Sensored vs. Sensorless

These are two common terms that you will see.  A sensorless motor is one that uses internal timing in the ESC to set motor speed.  The advantage is that the overall system is simpler.  The bad news is that, at low speeds, the ESC has no way of "knowing" which way the motor is turning.  Thus, you may pull the throttle forward and have your car shoot off in reverse.  This has happened to me before, and it's why I tend to adhere to sensored motors.

Sensored motors have something called a Hall effect sensor in them that judges the position of the rotor based on the magnetic field that the sensor "feels" at a given time.  The information is then relayed to the ESC and it can, from there, figure out if the motor is going forward, backward and at what speed.  Quite handy.  Thus, sensored systems tend to be smoother at low speeds, although "cogging" (lurching) is still a common problem.

Vortex Pro Race 2.5 Brushless Motor
Vortex Pro Race 2.5 Brushless Motor

This is the motor that I mention later in my article. The power is siimply phenomenal.

 
MRC ZD Racing 1/16 4WD Brushless Electric Truggy
MRC ZD Racing 1/16 4WD Brushless Electric Truggy

Brushless RTRs like this one are a great way to experience a new technology without hassle and without breaking the bank either. This one comes RTR with a battery, as well!

 

Turns and Kv

These are two of the most misunderstood terms/concepts in electric RC-car-dom. People often make the assumption that more turns = better, and they are stumped as to what Kv even refers to (a lot of publications even refer to it as kV, which is entirely wrong as I shall explain below).

Kv

This is a basic constant. In fact, the 'K' is German for Konstant. Guess what that means. The v refers to velocity. Thus, Kv is a velocity constant. The number associated with a motor simply means that, for every Volt of input, the motor will turn that many RPM (revolutions per minute). Thus, a 5000 Kv motor will turn 5000 times per minute faster as every Volt is added. At 8 volts, it would spin at 40000 RPM.

Turns

The number of turns that a motor has is roughly related to its power output.  A lower number of turns means, generally for a given manufacturer, a higher power output (measured in Watts).  But, you're probably wondering:

WHAAAATTT?

How does it make sense that fewer 'turns' means more power???  Well, consider: Turns are simply made of wire wrapped around the stator's phases.  Fewer turns means less wire.  Less wire means less resistance and, thus, a higher current can pass through the wire.  And, since power = current x voltage, more Amps = more POWERRR.

Cool.

Other stuff

 Brushless motors for RC cars are a relatively new technology.  They have truly prospered in the last few years, largely due to lower manufacturing costs and increased market competition.  Power levels have steadily ramped up over the years, too, and the most powerful 1/10 scale (540 size) motor that I know of is the one the I just recently purchased, the Team Orion Vortex 2.5.  It produces 897 Watts, which is 1.2 horsepower!

Add to that their smoothness, efficiency (usually over 85%) and cleanness compared to nitro engines, it's easy to see why the technology has blossomed as it has.

Comments 5 comments

3 years ago

What kind of Esc, battery set up would you recommend for that motor, great read man thanks.


LS 3 years ago

You'd need at least a GTB or better; that's what I use and it hasn't fried yet :P


dennis 3 years ago

i want to change my giant racer rc elec. boat from 3 brushed type motors to 1 brushless motor what all do i need parts etc.


LS 3 years ago

Not familiar with boats all that much, but by the sound of it you would need some sort of mount for the motor and a bracket to fill the space left over from the three motors. It really depends on how they're laid out in the hull, though. Are they all lined up along the prop shaft or are they all located around the shaft radially? And what type of clutch (I assume there is one) is being used? In terms of electronics, try to match the wattage of the motor you're going to with the three that you have. First figure out the approximate wattage of the ones you have (amps to each motor x voltage x # of motors). Then select a motor to suit your power demands that will fit your hull.


LS 3 years ago

Next, you will want to find a battery that can supply at least (IMO, it's not a hard guideline) 1.5x the current needed at peak by the motor. So motor current x battery voltage x 1.5. Amps from the battery can be determined with a LiPo by taking the C rating and multiplying it by the pack's capacity. so,

25 C x 1000 mAh = 25A peak current

All that's left to do is find a speed controller that can handle it (again, the 1.5 rule may apply here) and you're "sailing". Hope that helps!

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