linear-feedback-controller

A ros2_control package implementing linear feedback control strategies for robotic systems. It supports both fixed-base and free-flying robot configurations and is designed to integrate with external model predictive controllers.

The public message interface is defined in linear_feedback_controller_msgs.

Both packages are released under the BSD-2 license. Current versions are tracked in their respective package.xml files and must have an associated git tag of the form vX.Y.Z.

Full documentation is available on DeepWiki.

Controllers

The package provides three ros2_control controller plugins:

LinearFeedbackControllerRos

The main controller implements a two-phase control strategy:

1. PD phase — Proportional-derivative control for initial stabilization using configurable per-joint gains (p_gains, d_gains).
2. LF phase — Linear feedback control driven by an external controller (e.g. a whole-body MPC based on Crocoddyl).

The transition between phases is time-based and configurable via pd_to_lf_transition_duration.

The controller publishes sensor data on a ROS 2 topic:

• Base pose and velocity (free-flying robots; identity for fixed-base robots)
• Joint positions, velocities, and efforts

It receives control commands containing:

• A feedback gain matrix
• A feedforward torque term
• The linearization state

JointStateEstimator

Reads hardware state interfaces, applies exponential smoothing to joint velocities, and writes the filtered values to command interfaces. This makes raw sensor data suitable for downstream chainable controllers.

PassthroughController

Forwards and renames reference interfaces to command interfaces. Useful when simulation and hardware use different interface names but share the same parameter file.

Dependencies

Build

With colcon (recommended)

mkdir -p workspace/src
git -C workspace/src clone https://github.com/loco-3d/linear-feedback-controller.git
colcon build

With CMake directly

git clone https://github.com/loco-3d/linear-feedback-controller.git
cd linear-feedback-controller
mkdir _build && cd _build
cmake .. -DCMAKE_INSTALL_PREFIX=/path/to/your/install/folder
make install

With Nix

git clone https://github.com/loco-3d/linear-feedback-controller.git
cd linear-feedback-controller

# Check (build + tests)
nix flake check -L

# Build only
nix build -L

# Enter development shell
nix develop

nix-direnv is also supported for automatic shell activation.

Configuration

An example YAML configuration for the Tiago Pro robot is available at config/tiago_pro_lfc_params.yaml.

Real-world usage can be found in the agimus-demos repository, in particular in the agimus_demos_common package.

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