Motors - Aeroclub-IITM/UAV GitHub Wiki

Electrical machine that converts electrical energy into mechanical energy.Main mode of Actuation in robotics.Rotation of motors are controlled to make adequate thrust. Interaction between the motor's magnetic field and winding currents to generate force in the form of rotation.

motors

Different types of motors include DC, BLDC , Stepper etc.

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Output Characteristics of Interest - Angular Velocity ,Torque represented by kv and kt.

kv is a motor constant. It tells you how the generated back-emf in the motor relates to motor speed.

E(back emf)= kv*w ( w is the angular velocity)

But it doesn’t tell you how powerful the motor is or how much current it can handle or how efficient the motor is.

You can have a large motor and a small motor with the same Kv constant. The large motor will be more powerful than the small power. So there is no way to use Kv to tell you how powerful your motor is.

However, Kv is related to another important motor constant – Kt, the torque constant. Brushless Torque Constant, Kt

The motor torque constant for brushed DC motors and brushless motors tells you how current relates to torque.

T=Kt*I ( T is the torque, I is the current through motor )

Kt has units of Newton-meters per Amp.

K_t*K_v=1

BLDC

Brushless DC motor - But it is AC in every sense. Just like any other electric motor, a BLDC motor also has a stator and a rotor. Permanent magnets are mounted on the rotor of a BLDC motor, and stator is wound with specific number of poles. This is the basic constructional difference between a brushless motor and a typical dc motor.

There can be two types of BLDC motor on the basis of construction : (i) inner rotor design & (ii) outer rotor design.

For UAVs we are using outrunners.

● 3 Phase input

● Closed loop Feedback

β—‹ can be though 3rd wire , hall effect etc

● Commutation is entire electronic (Done by a ESC).As a result no physical contact between Rotor and Stator unlike DC Motors.

● Parameters of interest β—‹ KV = rpm required to create a back emf of 1V (no load) β—‹ Stator Dimension = Dimensions of the stator.

Why BLDC is used?

  • Power to weight ratio.

  • Efficiency

  • Response time

  • Longer life

  • Controllability

Working

Stator windings of a BLDC motor are connected to a control circuit (an integrated switching circuit). The control circuit energizes proper winding at proper time, in a pattern which rotates around the stator. The rotor magnet tries to align with the energized electromagnet of the stator, and as soon as it aligns, the next electromagnet is energized. Thus the rotor keeps running.

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