Brushless motors consist of two parts, a stator and a rotor. The rotor is typically made of permanent magnets and the stator of coils arranged along its diameter. If a current is applied through the coils a magnetic field is generated that attracts of detracts the rotor permanent magnets. If the appropriate current is applied, the coils will generate a magnetic field that will attract the rotor permanent magnets one after another and the rotor will keep rotating.
Brushless motor servo drives control the voltage and thus the currents flowing through the coils by switching high power transistors and using high performance microprocessors. The processor contstantly monitors the currents and position of the rotor and stator and uses closed loop control on order to achieve the desired position, velocity or torque that is commanded through a network interface.