Sixth、 External Control and Trajectory Planning
Developers of unmanned systems can generally be divided into two categories, bottom developers and top developers. Bottom developers need to directly contact the vehicle's sensors, actuators and other internal components, development tasks include fuselage structure design, power system selection, controller design, etc., more attention to the vehicle's own control and mobility performance. On the other hand, the upper level developers directly regard the unmanned vehicle as a whole (agent) or a controlled object, and obtain control instructions by designing the upper level intelligent planning algorithm and send them to the bottom level vehicle system to complete the expected task, paying more attention to the ability of intelligent perception and decision-making.
Remote control mode is a kind of control mode for human operation of UAV, which has a good effect in some UAV stunt performances. The remote control used in this section is the operation mode of "American hand", that is, the throttle and yaw control quantity corresponding to the left rocker, while the right rocker corresponds to roll and pitch. The RflySim platform supports conventional UAV remote control platforms currently on the market, and can achieve HITL and real flight experiments in this platform.
Mavlink is a communication protocol for small unmanned vehicles. The protocol is widely used in communication between Ground Control stations (GCS) and Unmanned vehicles, as well as in internal communication between the onboard computer and Pixhawk. The protocol defines the rules for parameter transmission in the form of a message library. The RflySim platform integrates the MAVLink protocol, which you can call directly in SITL, HITL, and real flight.
At the same time, Offboard mode is a control mode of UAV, which usually gives the on-board computer or the ground computer (upper computer) real-time control of the aircraft's speed, position, attitude, etc., and can treat the aircraft as a whole object, focusing on the top-level vision and cluster algorithm development.
CopterSim can communicate with PX4 in the following way. Whether it is UDP/TCP/ serial port, the packets sent follow the MAVLink protocol. For PX4 SITL mode, CopterSim can use UDP port to receive/send messages, but the number of vehicles in this mode is limited to 50; The PX4_SITL_RFLY provided by the RflySim platform can support large-scale clusters, up to 1000 vehicles without port conflicts. In HITL CopterSim will communicate with PX4 via serial port.
6.3. Frequently Asked Questions in this chapter
Issue 5: External control and trajectory planning (Part 1）
Issue 5: External control and trajectory planning (Part 2)
Issue 5: External control and trajectory planning (Part 3)