Offboard Control using ROS2. How to achieve velocity control?

ROS / MAVROS / MicroDDS
1

Goodmorning,
I am trying to achieve velocity control using ROS2. I have been trying to modify the offboard control example (this one: ROS 2 Offboard Control Example | PX4 User Guide, provided in px4_ros_com/src/examples/offboard/offboard_control.cpp), obtaining poor results.

As I have understood, it is possible to control velocity only while reaching the specified position. I don’t have problems in controlling the position.

I tried different approaches, as:

set only msg.velocity to true

void OffboardControl::publish_offboard_control_mode() const {
OffboardControlMode msg{};
msg.timestamp = timestamp_.load();
msg.position = false;
msg.velocity = true;
msg.acceleration = false;
msg.attitude = false;
msg.body_rate = false;

offboard_control_mode_publisher_->publish(msg);

}

and then setting

void OffboardControl::publish_trajectory_setpoint() const {
TrajectorySetpoint msg{};
msg.timestamp = timestamp_.load();
msg.vz = -5.0;

trajectory_setpoint_publisher_->publish(msg);

}

However the quadcopter stops rising at a certain altitude, and I don’t understand why. Can someone help me? Thanks in advance.

2

In the end I solved the problem by setting msg.x, msg.y of TrajectorySetpoint equal to NaN, in this way I was able to control in speed.

3 Likes
4

can you share your complete example? i am trying to have both position and velocity control at teh same time, but cant seem to get it to work.

5

Have you found out how to do this? I’m trying right now to implement this on my project.

6

I would also like to see the example because I’m also trying this for some time.

7

How did you set NaN in the message?

8

Hi, for people that come across this question and don’t know how, you can set a value to NaN by using the C++ nan constant, or in Python using float("nan") (source).