Unmanned Systems Technology 007 | UMEX 2016 report | Navya ARMA | Launch & recovery systems | AIE 225CS | AUVs | Electric motors | Lethal autonomous weapons

69 performance curve characteristics. The major difference between the two is the use of brushes: BLDC motors do not have brushes and must be electronically commutated – commutation is the act of changing the motor phase currents at the appropriate times to produce rotational torque. In a brushed dc motor, the motor assembly contains a physical commutator that is moved by means of actual brushes in order to move the rotor. In a brushless motor the mechanical switching function, implemented by the brush and commutator combination in a brush-type motor, is replaced by electronic switching. In a typical brushless motor, the electromagnetic field (created by permanent magnets) is the rotating member of the motor and is called the rotor. The rotating magnetic field is generated by a number of electromagnets commutated with electronic switches, typically transistors, in the right order at the right speed. In a brushless motor it is important to know when to switch the electrical energy in the windings to perpetuate the rotating motion. This is typically accomplished by some means of feedback designed to provide an indication of the position of the magnet poles on the rotor relative to the windings; a Hall effect device, a transducer that varies its output voltage in response to a magnetic field, is commonly used for providing this positional feedback. For unmanned systems it is more common for brushless motors to be commutated without sensors (sensorless) or with the use of an encoder for positional feedback. A BLDC motor has two primary parts – the rotor, the rotating part; and the stator, the stationary part. Other important parts are the stator windings and the rotor magnets. There are two categories of brushless motors, outrunner and inrunner; with multi-rotor and most unmanned fixed- wing aircraft you will only encounter outrunner motors. The difference is that outrunners have the rotor on the outer area of the motor, while with inrunners the rotating part is on the inside, the outer shell remaining stationary. Inrunners are often used in remote control cars, as they can spin much Electric motors | Focus Unmanned Systems Technology | April/May 2016 Brushless motors are an established technology. This is a 28-pole type (Courtesy of Hacker Motor) Brushless electric motor technology, on which electric drive systems in unmanned platforms are based, is used in many other applications