Basic principles of drone autonomous control
Basic principles of drone autonomous control
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A simple way to achieve autonomous control consists in structuring multiple control-loop layers, such as hierarchical control systems. The low-layer loops (i.e. for flight control) can tick as fast as 100 times per second, and the higher-level loops can be required cycles with lengths around a second. The principle is to decompose the aircraft’s behavior into easily manageable “chunks”, or states, with knowledgeable transitions between them.
Hierarchical control system types range from the simple scripts, to finite state machines, behavior trees and hierarchical task planners. Basic levels of autonomy are handily resolved using proprioceptive sensors, that give information about the aircraft state. Advanced autonomy calls for situational awareness, gaining knowledge about the environment surrounding the aircraft: sensor fusion aggregates different information provided by multiple sensors. Exteroceptive sensors deal with fully external information like range measurements, while exproprioceptive ones correlate internal and external states.
Basic principles of drone autonomous control
Examples of mid-layer algorithms:
- Path planning: Determining an optimal path for vehicle to follow while meeting certain objectives and mission constraints, such as obstacles or fuel requirements
- Trajectory generation (motion planning): Determining control maneuvers to take in order to follow a given path or to go from one location to another using optimized techniques and processes
- Trajectory regulation: The specific control strategies required to constrain a vehicle within some tolerance to a trajectory.
- Evolved UAV hierarchical task planners use methods like state tree searches or genetic algorithms.
Autonomous modes
- UAV manufacturers often offer built-in autonomous modes
- Self-level: the aircraft stabilizes its altitude by itself using on-board sensors.
- Hover: altitude stabilization is reinforced by attitude stabilization on the pitch, roll and yaw axis. The latter can be achieved by sensing GNSS coordinates, called alone position hold.
- A feature called by some designers care-free: the aircraft radio control will free the operator from managing the impact of the aircraft heading on the roll and yaw controls.
- Autonomous take-off and landing
- Failsafe: the UAV will land automatically as soon as the control signal is lost.
- Return-to-home
- Follow-me
- GPS waypoint navigation
- Pre-programmed tricks like rolls, loops…
UAV’s degrees of autonomy
- Autonomy degrees : As for general robotics, the amount of independency of the UAV is often referred as degree of autonomy.
- Full degree of autonomy is currently reached for low levels of autonomy akin to simple particular tasks, which can be illustrated with autonomous airborne refueling[54] or ground-based battery switching for example.
- Autonomy levels : Higher-level tasks call for greater computing, sensing and actuating capabilities.