This chapter provides a very basic overview of the operational principles of electric motors.

The operation of an electric motor (machine) is based on the phenomenon of electromagnetic induction – the interaction of a conductor with an electric current and magnetic field. There are three fundamental concepts of implementation of an electric motor:

A permanent magnet (or electromagnet) motor

The current in the conductor influences the flux induced by a permanent magnet (or electromagnet) or opposite transformation.

In the figure:

	I – The direction of the flowing current;
	B – Direction of magnetic flux created by the permanent magnets
	F – Force and its direction created by current and magnetic flux
	In green – rotating contact surface enabling to change the direction of current 
		   while the motor is rotating.
	In orange – conductor (a copper wire)

The created force creates momentum on the conductor i.e. it starts to rotate. During rotation the conductor changes the connection to the contact surfaces, thus changing the current direction in the conductor. The created momentum keeps turning the conductor and the motor keeps running.

A rigid body motor

The current of the conductor influences a secondary magnetic flux induced by an electric current.

In this case, a force on the rotating rigid magnetic body is created by two stator coils, where the flowing currents U1 and U2 differ in their phase i.e. the force is created by the phase shift.

Magnetic flux motor or Brushless motor

The magnetic flux induced by the current influences a ferromagnetic body (so-called reluctance principle). This type of motor is widely known as brushless direct current motors and widely used in different autonomous systems like drones due to the ability to provide a high output power relative to its size.

The motor consists of a stator – coils and robots – permanent magnets (or single multi-pole magnet). If a direct current is applied to the pair of opposite coils a force and appropriate momentum is created on the magnets (figure on the left). If a control circuit keeps switching one pair of coils after another, the rotor will keep rotating due to sequentially generated force and momentum.

In all cases, a dedicated motor controller is used to ensure the proper application of voltage and current to the motor. Other types of motors are derived from the mentioned ones.