Application Programming Interface
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We provide open source API for development with the Kerloud Flying Rover series, and candidate API interfaces will support C++, python and other languages. Details will be updated continuously in this part.
The API in ROS (Robot Operating System) is implemented based on the official from the PX4 community.
Our maintained repositories are:
mavros (dev_flyingrover branch):
mavlink (dev_flyingrover branch):
An offboard control example with the ROS C++ API (dev_flyingrover branch):
More programming details will be illustrated in the tutorial section . We present here topics and services that are specifically related with our flying rover case.
This topic can be subscribed to obtain current flying rover state. The message type is , which is extended from the original version. An extra field, namely flyingrover_state, is provided to indicate the flying rover state, shown as follows. The candidate values for this field are those constants defined with the prefix FLYINGROVER_STATE_*.
For clarity, we illustrate the meanings here:
flyingrover_state=0: the flying rover is not initialized yet;
flyingrover_state=1: the flying rover is operating in the rover mode;
flyingrover_state=2: the flying rover is operating in the multicopter mode;
flyingrover_state=3: the flying rover is in transition from the rover to the multicopter mode. The state will turn to the multicopter in manual mode instantaneously, or when the speed is lower than the param FR_V_TH_MC value (0.2m/s by default) in autopilot firmware in the offboard or other auto modes;
flyingrover_state=4: the flying rover is in transition from the multicopter to the rover mode, and it will tend to land manually or autonomously. The state will turn to the rover mode after landing;
To illustrate, if we'd like to switch to the multicopter mode, then the service has to be called with settings below:
To switch to the rover mode reversely,
Similar with the ROS API in C++, ROS python API is implemented on basis of our maintained mavros and mavlink packages as well. The only difference is that all those topics and services mentioned above should be utilized with python.
Our maintained repositories are:
move(x,y,z, BODY_FLU=False): request the vehicle to move to a desired position defined in either FLU frame or ENU frame, applicable in both rover and multicopter modes.
turn(yaw_degree): request the vehicle to turn to a desired yaw angle, applicable in multicopter mode only.
land(): request the vehicle to land in multicopter mode.
hover(): request the vehicle to hover at current position in multicopter mode.
arm(): request to arm the vehicle.
disarm(): request to disarm the vehicle on ground.
transit_to_rover(): request the vehicle to transit to rover mode.
transit_to_mc(): request the vehicle to transit to multicopter mode.
return_home(height): request the vehicle to return home, applicable in multicopter mode only.
This topic is used to publish the position setpoint in the local or global frame for both rover and multicopter modes. Note that the reference frame in the ROS level is the ENU frame, while that for the autopilot is the NED frame. The message type is or respectively.
These two topics are used to publish the velocity setpoint in the local frame for both rover and multicopter modes. The only difference between them is whether the velocity information is with a timestamp or not. The message type is .
These two topics can be utilized to set the attitude setpoint for both rover and multicopter modes, although it's recommended to use in the rover mode only. The message types are and respectively. The attitude thrust is directly fed into the main rotor throttle for the rover, and the yaw angle tracking error will be computed to generate the servo control input for steering.
This service is utilized for mode switching between the rover and multicopter modes in the offboard operation. The message type is . It corresponds to a customized mavlink message (mavlink::common::MAV_CMD::DO_FLYINGROVER_TRANSITION) in .
Note that the mavlink::common::MAV_FLYINGROVER_STATE enumeration is defined and presented below:
mavros:
mavlink:
An offboard control example with the ROS python API:
The code is explained in the tutorial section . For brevity, the low level message communication is handled within the Px4Controller class, and the friendly API for user programming is wrapped within the Commander class, partially listed below: