# Autonomous flight¶

One of the core functionalities of the ROSflight autopilot is to allow the onboard computer to send control setpoints to the embedded flight controller. These setpoints would typically be computed by a controller running as a ROS node, normally on the onboard computer.

## Provide control from an onboard computer¶

Control setpoints are sent to the autopilot by publishing to the /command topic that is advertised by the rosflight_io node. This topic accepts message of type rosflight_msgs/Command, which have the following structure:

std_msgs/Header header
uint8 mode
uint8 ignore
float32 x
float32 y
float32 z
float32 F


The header field is a standard ROS message header. The x, y, z, and F fields are the control setpoint values, which are interpreted according to the mode and ignore fields.

The following table describes the different values that the mode field can take, as well as how the setpoint values are interpreted for each of these modes:

Value Enum x y z F
0 MODE_PASS_THROUGH aileron deflection (-1 to 1) elevator deflection (-1 to 1) rudder deflection (-1 to 1) throttle (0 to 1)
1 MODE_ROLLRATE_PITCHRATE_YAWRATE_THROTTLE roll rate (rad/s) pitch rate (rad/s) yaw rate (rad/s) throttle (0 to 1)
2 MODE_ROLL_PITCH_YAWRATE_THROTTLE roll angle (rad) pitch angle (rad) yaw rate (rad/s) throttle (0 to 1)

The MODE_PASS_THROUGH mode is used for fixed-wing vehicles to directly specify the control surface deflections and throttle, while the MODE_ROLLRATE_PITCHRATE_YAWRATE_THROTTLE and MODE_ROLL_PITCH_YAWRATE_THROTTLE modes are used for multirotor vehicles to specify the attitude rates or angles respectively.

The ignore field is used if you want to specify control setpoints for some, but not all, of the axes. For example, I may want to specify a throttle setpoint to perform altitude hold, but still let the RC pilot specify the attitude setpoints. The ignore field is a bitmask that can be populated by combining the following values:

Value Enum Result
0 IGNORE_NONE Ignore none of the fields (default)
1 IGNORE_X Ignore the x field
2 IGNORE_Y Ignore the y field
4 IGNORE_Z Ignore the z field
8 IGNORE_F Ignore the F field

For the previous example, I would set the ignore field to a value of

ignore = IGNORE_X | IGNORE_Y | IGNORE_Z


The best practice is to use enum names rather than the actual numeric values for the mode and ignore fields. For example, to specify a multirotor attitude angle command in C++ I might have

#include <ros/ros.h>
#include <rosflight_msgs/Command.h>

rosflight_msgs::Command msg;
msg.mode = rosflight_msgs::Command::MODE_ROLL_PITCH_YAWRATE_THROTTLE;
msg.ignore = rosflight_msgs::Command::IGNORE_NONE;
msg.x = 0.0;
msg.y = 0.0;
msg.z = 0.0;
msg.F = 0.6;

and in Python I might have
import rospy
from rosflight_msgs.msg import Command

msg = Command()
msg.mode = Command.MODE_ROLL_PITCH_YAWRATE_THROTTLE
msg.ignore = Command.IGNORE_NONE
msg.x = 0.0
msg.y = 0.0
msg.z = 0.0
msg.F = 0.6

I would then publish this message to the /command topic to forward it to the embedded flight controller.

## Fly waypoints with ros_plane or ros_copter¶

Waypoint following is not supported natively by the ROSflight stack. However, the ROSplane and ROScopter projects are good example implementations of how to achieve this using ROSflight. They also provide good examples of how you might go about integrating your own guidance or control algorithms with the ROSflight stack.