Basic Info

Description of contribution in a few bullet points

As discussed in #6032 I added motion models for the mppi controller as plugins instead of hardcoded modes.
In this way it is possible for an user to add its own motion model and constraints.

Custom plugins can be added in another package and used with:

      motion_model: "my_motion_model" 
      my_motion_model:
        plugin: "my_pkg::MyMotionModel"
        random_parameter: 0.1 # a parameter to do something

Description of documentation updates required from your changes

plugin needs to be specified with parameters. For example, instead of:

motion_model: "Ackermann"
AckermannConstraints:
    min_turning_r: 0.2

Now is:

      motion_model: "ackermann" 
      ackermann:
        plugin: "mppi::AckermannMotionModel"
        min_turning_r: 0.4  # Minimum turning radius in metres

Implementation notes

I tried to keep the modifications at minimum, some notable changes are:

• Check for motion model type is no more done using a static cast but uses hasConstrainedTurningRadius and isHolonomic().
• motionModel.initialize() has been renamed setConstraints(). A new initialize() method is used to retrieve the plugin specific parameter since constructors must be without arguments now that the motion model is a plugin.

Description of how this change was tested

First I ensured that the package nav2_mppi_controller compiles correctly and I run the tests of the nav2_mppi_controller package (colcon test ...) to see if they passed.

I created some node to test the correct behavior with a dummy empty global costmap, a local costmap containing some obstacles and a node that emualtes actuation by converting velocity commands into TF publishing.
I verified that the existing motion models works correctly:

• with mppi::DiffDriveMotionModel motion model only vx and wz is used
• with mppi::OmniMotionModel motion model also vy is used
• with mppi::AckermannMotionModel motion model the velocity uses the minimum turning radius

I also created a new motion model StraightOnlyMotionModel that can only go straight and it works.

Future work that may be required in bullet points

• I created a new file (motion_models.cpp) and had to put a copyright notice on it to pass the checks, i used "// Copyright (c) 2026 Open Navigation LLC", don't know if it is ok
• Don't know if using the mppi:: namespace for the motion models is ok

For Maintainers:

• Check that any new parameters added are updated in docs.nav2.org
• Check that any significant change is added to the migration guide
• Check that any new features OR changes to existing behaviors are reflected in the tuning guide
• Check that any new functions have Doxygen added
• Check that any new features have test coverage
• Check that any new plugins is added to the plugins page
• If BT Node, Additionally: add to BT's XML index of nodes for groot, BT package's readme table, and BT library lists
• Should this be backported to current distributions? If so, tag with backport-*.