Custom hardware interface type

Question

I would like to write a controller that needs all joint states to update a single joint.

My idea was to create a class MyStateInterface which inherits from hardware_interface::StateInterface and stores all information for each joint. Then, I would like to export this class inside the hardware interface to pass the joint information to the controller.

To make it clear, I modify this example:

std::vector<double> hw_states_;

CallbackReturn MyRobotHardware::on_init(const hardware_interface::HardwareInfo & info) {
  // set some default values when starting the first time
  hw_states_.resize(info_.joints.size(), 0.0);
  return CallbackReturn::SUCCESS;
}

std::vector<hardware_interface::StateInterface>
MyRobotHardware::export_state_interfaces()
{
  std::vector<hardware_interface::StateInterface> state_interfaces;

  for (uint i = 0; i < info_.joints.size(); i++)
  {
    state_interfaces.emplace_back(hardware_interface::StateInterface(
      info_.joints[i].name,                  // joint name from controller.yaml
      hardware_interface::HW_IF_POSITION,    // "position"
      &hw_states_[i]                         // the joint value
    ));
  }

  return state_interfaces;
}

To something like this:

std::vector<MyStateHandle> hw_states_;

CallbackReturn MyRobotHardware::on_init(const hardware_interface::HardwareInfo & info) {
  // set some default object when starting the first time
  hw_states_.resize(info_.joints.size(), MyStateHandle());
  return CallbackReturn::SUCCESS;
}

std::vector<hardware_interface::StateInterface>
MyRobotHardware::export_state_interfaces()
{
  std::vector<hardware_interface::StateInterface> state_interfaces;

  for (uint i = 0; i < info_.joints.size(); i++)
  {
    state_interfaces.emplace_back(hardware_interface::StateInterface(
      info_.joints[i].name,      // joint name from controller.yaml
      "my_state_handle",         // a made up name
      &hw_states_[i]             // information for controlling the joint
    ));
  }

  return states_interfaces;
}

This didn't work because there is no matching function for the call hardware_interface::StateInterface(const std::string &name, const std::string &interface_name, MyStateHandle *value_ptr=nullptr) because there is only the function hardware_interface::StateInterface(const std::string &name, const std::string &interface_name, double *value_ptr=nullptr)

I want to know if there is a way to pass a class full of control data from the hardware interface to the controller, or am I on a completely wrong track?

Answer 1

No this is not possible yet. But we are working on that feature, see this PR here. This feature might come with Jazzy.