Robotics

Reference design for drone motor controller

5th May 2017
Lanna Cooper

 

The ability to quickly change the speed and rotational direction of its motors is the key to a drone’s performance, which makes the ESC (Electronic Speed Control) module a very important subsystem. Faster motor speed changes also make for greater stability, which saves energy thereby enabling longer flight times.

Typically, non-military drones use three phase, brushless motors (wound stators with permanent magnet rotors). While these motors have several advantages - including better reliability - over older DC motors that used mechanical commutation and brushes, they do require complex electronic control circuits.

However, thanks to microcontrollers, computationally intensive control schemes can be implemented to achieve better dynamic performance, such as FOC (Field-Oriented Control), which decouples torque from magnetisation control and maintains efficiency over a wide range of speeds.

Knowing the position of the rotor is fundamental to implementing FOC; to generate maximum torque, the angle between the rotor field and the stator field must be equal to 90°. Rotor positional information can be measured by sensors, or - when space is at a premium - derived, using an algorithm based on various current and voltage measurements, in which case it is called 'sensorless'.

All this may sound complicated. But a reference design eases the pain. The 'High-Speed Sensorless-FOC Reference Design for Drone ESCs' implements an ESC that can be used for UAV (Unmanned Aerial Vehicles) or drones, or battery-operated power tools, for that matter. It supports two to six LiPo cells and can even estimate temperature from winding resistance changes to protect the motor during temporary overloads.

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