Motors

This section discusses quadcopter motors.

KV Rating

The motors used on quadcopters come with a KV rating. The KV rating does not refer to kilo-Volts but rather to a velocity rating constant which relates to the motor’s revolutions per minute when a 1V potential is applied to the motor with no load.

Propellors

As a general rule of thumb: the higher the KV rating of the motor the smaller the propellor should be. A lower KV rated motor with a correspondingly larger propellor lifts more weight, uses less current and should be easier to fly steadily. Conversely, higher KV rated motors with correspondingly smaller propellors allow for geater speed but at the cost of reduced efficiency.

Propellors are designated using three measurements. The first is the length. This is typically given in inches. The second measurement is the propellor pitch. The pitch rating defines how far the propellor would drive forward for a single revolution. The greater the pitch the greater the thrust. Thirdly is the bore measurement which refers to the hole in the centre of the propellor.

So a propellor that has a designation of 9545 has a length of 9”, will drive forward 4.5” when 1V is applied and has a bore measurment of 5mm.

Batteries

The community standard is the Lithium-Polymer or LiPo battery. These kinds of batteries are light weight, compact and offer high discharge rates. These kinds of batteries are made up of multiple cells. A single cell provides a nominal 3.7 Volts. To provide higher voltages these cells are connected in series and have a “S” designation. So a 4S battery holds 3.7 x 4 = 14.8 Volts.

LiPo batteries also carry a “C” rating which indicates the maximum discharge rate. The “C” stands for capacity. So a 25C battery can discharge at 25 times its capacity.

The third important measurement for a battery is its capacity which is provided in milli-Amp hour (mAh) values. So a 2200 mAh battery with a 25C rating can discharge 25 x 2200 = 55000 mA or 55 Amperes.

With an understanding of this information you should now be able to determine the appropriate battery for your quad. The discharge rate should be higher than the combined draw from your ESC’s and motors.