UAS Components: Flight Controller

Flight Controller and Automation

Put simply, the flight controller is the “brains” of the drone. It takes in information sent to it by the remote controller, GPS, obstacle avoidance sensors, and other components and then sends signals to the motors to properly respond to the information.

For instance, if you were flying a drone and pushed forward on the control stick, you would be sending a signal to the flight controller to move the drone forward. If this were a GPS drone (in GPS mode), you would effectively be telling the flight computer to move the drone to a GPS location further in front of where it is now. The flight controller would check with the GPS to gather information, then fire up the rear motors (if on a quadcopter) to move the drone in a forward direction.

The majority of higher-end drones on the market today also feature autopilot built into the flight controller. The flight controllers and autopilot also have various intelligent flight modes. These automated systems are useful for different applications and help improve the overall safety of a drone operation.

Autopilot systems are programmed to take over if there is a lost-link. The lost-link occurs when the drone and the controller are no longer communicating with each other. Lost-links can occur because of interference, signal loss behind a building, etc. If the link is lost the autopilot software works in conjunction with the flight controller to maintain aircraft control.

There are different interfaces that the autopilot system will interact with throughout flight. GPS, accelerometer/gyro, magnetometer, ext. pilot, payload, flight surfaces, airspeed/altimeter, and lastly, the C2 datalink. Many drones on the market today have obstacle avoidance sensors that communicate to the autopilot. The sensors tell the drone where it's at and whether it is flying too close to an obstacle.

The heart of an autopilot system is the microcontroller, which is also called the processor. The microcontroller collects sensor values, command inputs, and computes calculations for heading correction, etc. When the microcontroller is done with calculating, it will instruct the flight controls on what to do.

Controllers usually operate on two different loops, there is an inner and outer loop. The inner loop operates at higher speeds and is responsible for wind and keeping the aircraft airborne. The outer loop focuses on the actual navigation of the aircraft. The outer loop operates at a much slower speed compared to the inner loop. Whether operating on the inner or outer loop, they can only focus on one task. The functions that are performed by the autopilot are all done in a sequence.

The sequence is controlled by a clock pulse that dictates the order of when and what tasks will be completed next. The clock's job is to keep all of the components and functions of the drone in sync. The clock signal is created by regular vibrations of a quartz crystal vibrating when voltage is introduced. The synchronization can be interrupted—this is done for high-priority tasks. The interruption is often triggered by an internal timer that breaks the list that the controller follows. The sequence may be interrupted if the drone is trying to interpret its current location based off the GPS.

Flight controllers and automation are continually becoming more advanced. Automation has been used in manned aircraft for decades and the technology is really taking off in the unmanned market.