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I followed ros2_control diff_drive_example https://github.com/ros-controls/ros2_control_demos/tree/master/example_2 to bring my ROS1 robot to ROS2.

I notice there is a PID controller (pid.cpp and pid.hpp files) in ros2_control and I wonder if I have to implement/use it in my hardware_interface by my own or if it will already be used by diff_drive_controller itself?

In my previous code for ROS1, there was a class PID which inherited from control_toolbox::PID https://github.com/hoverboard-robotics/hoverboard-driver/blob/master/include/hoverboard_driver/pid.h and which acts as an interface between dynamic reconfigure and control_toolbox::Pid. Inside the Hardware_interface itself, there was an instance of control_toolbox:Pid (actually of the new pid class which inherits from control_toolbox::Pid) for each wheel like this

    // Init PID controller
pids[0].init(nh_left, 1.0, 0.0, 0.0, 0.01, 1.5, -1.5, true, max_velocity, -max_velocity);
pids[0].setOutputLimits(-max_velocity, max_velocity);
pids[1].init(nh_right, 1.0, 0.0, 0.0, 0.01, 1.5, -1.5, true, max_velocity, -max_velocity);
pids[1].setOutputLimits(-max_velocity, max_velocity);

and this was just used before sending commands to Hardware by serial like this

    double pid_outputs[2];
pid_outputs[0] = pids[0](joints[0].vel.data, joints[0].cmd.data, period);
pid_outputs[1] = pids[1](joints[1].vel.data, joints[1].cmd.data, period);

// Convert PID outputs in RAD/S to RPM
double set_speed[2] = {
    pid_outputs[0] / 0.10472,
    pid_outputs[1] / 0.10472
};

Now I wonder if I still need to implement PID to Hardware_interface by myself or if the controller will already handle this for me.

I couldn't find an example for diff drive together with PID which makes me curious if it is needed or not

Patrick

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1 Answer 1

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Unfortunately, we don't have a released PID controller yet. But there is one PR for it, I hope it gets attention again after ROSCon.

ros2_control supports controller chaining, but diff_drive_controller needs an update to support chaining with the PID controller above.

control_toolbox::PID is also released for ROS 2, I fear that you have to implement that in the hardware component as you are suggesting.

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  • $\begingroup$ Thanks for your quick answer. In this case, I'll implement in the way it has been done before, no issue. I just wanted to ensure that I'm doing it the "right" way. $\endgroup$ Oct 11, 2023 at 11:03

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