Controllers

All three controllers share kontrolem_controllers_base: the artifact loader, the deviation-state assembly, the validity guard, the chainable plumbing, and the two numeric cores. A controller package is thin — it pins the accepted artifact controller_type and picks the flavor (static gain vs dynamic compensator).

• lqr_controller
• lqg_controller
• hinf_controller

Shared architecture

• State. On every update the base reads joint positions (and velocities, when the law needs them), forms x = [q − q_eq, q̇], and runs the validity guard before computing a command.

• Cores. StateFeedbackController uses the static-gain core (u = u_eq − K·x); OutputFeedbackController uses the dynamic-compensator core (ξ̇ = ctrl_A·ξ + ctrl_B·y, u = u_eq + ctrl_C·ξ + ctrl_D·y), Tustin-discretized once in on_configure().

• Realtime. The per-cycle path is allocation- and lock-free: preallocated Eigen, .noalias() products, a lock-free buffer for the reference topic. An instrumented test asserts zero heap traffic across many cycles.

Chaining

Because each controller is a ChainableControllerInterface, an upstream controller can drive its setpoint by claiming its exported reference interfaces. Example cascade (lqr_controller’s config/lqr_chained_controllers.yaml): a stock forward_command_controller writes the LQR controller’s position references.

controller_manager:
  ros__parameters:
    lqr_controller:
      type: lqr_controller/LqrController
    reference_generator:
      type: forward_command_controller/ForwardCommandController

reference_generator:
  ros__parameters:
    joints:
      - lqr_controller/cart_joint   # <downstream>/<joint>
      - lqr_controller/joint1
      - lqr_controller/joint2
    interface_name: position

When the upstream activates and claims lqr_controller/<joint>/position, the controller manager puts lqr_controller into chained mode: it then reads its setpoint from those reference interfaces instead of the ~/reference topic. The whole cascade is YAML — no custom upstream code.