Let’s start with the basics, we work in direct current, so how does an electric motor work? A simple DC electric motor moves because there is an electromagnetic field that attracts the opposite side of the rotor until it reaches a certain position where brushes (1 and 2) in contact with the positive and ground change the polarity so that the opposite side of the rotor is attracted again to create a continuous motion, such as the k55 motor that runs so well.
Do brushless motors have any problems?
In large engines: No problem, everything works perfectly well with high performance because friction is negligible. In small motors: The brushes, with a minimum friction, cause a great decrease in performance and prevent small motors of high power.
Therefore, for a project like ours where we need small motors, we will have to eliminate the brushes.
There are brushless motors on the market, but they are still normal electric machines, but what about electric machines? They operate on alternating current and our battery delivers direct current. We will have to get alternating current to run these motors (ideally sinusoidal, although in practice PWM (Pulses of Modulated Width) will be used). This is where the drives or ESC’s come into play. Note: Usually used three-phase for this type of motors.
How do brushless motors work?
These brushless motors allow us to achieve high performance and high power in exchange for high consumption. Because of this, we have to use Lypo batteries (Lithium polymer), they are low energy density batteries compared to others but with a unique feature, can deliver a lot of power because brushless motors need the order of 10 A to 11 v.
Kv, the basic feature of a brushless motor: This constant (it is almost a constant) simply means the number of revolutions (RPM) given by the motor for each continuous volt applied to the ESC (A maximum power). That is to say that if we apply 11.1v to an 1100 Kv engine, it will run at 12210 RPM maximum (with the ESC you can decrease it). This is its nominal speed and it will never go up faster unless we increase the potential difference (Voltage).
Where do you buy brushless motors?
- Higher efficiency (less heat loss)
- Higher performance (longer battery life for the same power)
- Less weight for the same power
- Less maintenance required due to brushless brushes
- Speed/torque ratio is almost a constant
- More power for the same size
- Improved heat dissipation
- High speed range without mechanical limitation.
- Less electronic noise (less interference to other circuits)
- Higher construction cost
- The control is by means of an expensive and complex circuit
- Electronic control is always needed to make it work (ESC’ s), which sometimes doubles the cost