Attitude offboard control example?

[brunojnguerreiro]

First, I'd like to thank you for your great work on this repo. I'm trying to have a MWE for an off-board outer loop controller that in each instant receives pose and velocity data from a crazyflie (with lighthouse), and sends a low-level command for rpyt, fullState, or other method. I've played a bit with the examples, in simulation and in real experiments, creating different way to send HL or fullState commands to the CFs. I've also managed to change crazyflies.yaml to get the pose into a ros topic and also create other custom and more efficient messages for higher data rate transfer for off-board use. Nonetheless, I'm struggling on how to access the pose or custom topics in a script such as "crazyflie_examples/crazyflie_examples/cmd_full_state.py". Could you guide me in getting a MWE for this purpose?

[knmcguire]

Hi! I've looked quickly in the crazyflie python class and unfortunately it does not seem that there is a logging functionality in that class, and I'm not sure if this feature will be added anytime soon...

Luckily it shouldn't be too difficult to write a subscriber to those topics in ROS2. Have you tried getting something to work with the help of these ROS2 tutorials? https://docs.ros.org/en/humble/Tutorials/Beginner-Client-Libraries/Writing-A-Simple-Py-Publisher-And-Subscriber.html

[brunojnguerreiro]

Well, I kind of want to do both, depending on the background of the students in each course, but I can manage the conversion myself. I though the "cmd_full_state" was the recommended alternative to the cmd_vel_legacy. As I'm using the cpp backend, does it also support the cmd_vel_legacy, or should I switch to the cflib?

[knmcguire]

Hmmm..... perhaps that is a question for @whoenig... but I'm not sure if that will be possible with just cmd_full_state of just controlling accelerometers.

cpp link should also work as it has cmd_vel_legacy implemented as well

crazyswarm2/crazyflie/src/crazyflie_server.cpp

Lines 593 to 600 in 9f56069

	void cmd_vel_legacy_changed(const geometry_msgs::msg::Twist::SharedPtr msg)
	{
	float roll = msg->linear.y;
	float pitch = - (msg->linear.x);
	float yawrate = msg->angular.z;
	uint16_t thrust = std::min<uint16_t>(std::max<float>(msg->linear.z, 0.0), 60000);
	// RCLCPP_INFO(logger_, "roll: %f, pitch: %f, yaw: %f, thrust: %u", roll, pitch, yawrate, (unsigned int)thrust);
	cf_.sendSetpoint(roll, pitch, yawrate, thrust);

[whoenig]

The idea is to have different cmdtopics for different use-cases. CmdFullState is for trajectory tracking, i.e., if you want to follow desired position, velocity, and acceleration commands. Others are defined in the firmware here: https://github.com/bitcraze/crazyflie-firmware/blob/master/src/modules/src/crtp_commander_generic.c. Not all are implemented in Crazyswarm, but it's pretty easy to add them. The legacy control mode is a bit tricky, because parameters can actually change the behavior (e.g., one can select if the values mean absolute angles or rates), see https://github.com/bitcraze/crazyflie-firmware/blob/master/src/modules/src/crtp_commander_rpyt.c.

[brunojnguerreiro]

Thank you @whoenig and @knmcguire, I now have a better understanding of what I can do. I'm trying to use the legacy_cmd_vel topic with cpp backend. I'm publishing the message yet nothing is happening to the drone, besides stopping the motors if at hover before. Even with a simple message with all zeros but the z linear component at 10000 (above minimum and below maximum values for thrust). Do I need to configure any parameter to be able to control the crazyflie like this?

[knmcguire]

Hi! Make sure that you first send a couple of all zeros to that command first. That is a safety mechanism to not have the crazyflie immediately take off if you connect a controller with wrongly configured sticks. But that might be a bit tricky if you are already in the air though.. 🤔 You can find that explanation for the cflib in here https://www.bitcraze.io/documentation/repository/crazyflie-lib-python/master/user-guides/python_api/#sending-control-setpoints-with-the-commander-framework

Perhaps when it is still on the ground, first send the all zero attitude command while it is starting up? Then takeoff and send the attitude command again?