Autonomous Flight¶
One of the core functionalities of the ROSflight autopilot is to allow the companion 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 companion computer.
Provide Control from a Companion Computer¶
Control setpoints are sent to the flight controller by publishing to the /command topic that is advertised by the rosflight_io node. This topic accepts messages 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 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 throttle setpoints to perform altitude hold, while still letting 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.header.stamp = ros::Time::now();
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;
In Python I might have:
import rospy
from rosflight_msgs.msg import Command
msg = Command()
msg.header.stamp = rospy.Time.now()
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
/command topic to forward it to the embedded flight controller.
Note
If the flight controller does not receive a new command for a defined period of time, it will ignore the old commands and revert to RC control. The length of this timeout period is set by the OFFBOARD_TIMEOUT parameter.
Fly Waypoints with ROSplane or ROScopter¶
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.