Rotation Shim Controller

Source code on Github.

The nav2_rotation_shim_controller will check the rough heading difference with respect to the robot and a newly received path. If within a threshold, it will pass the request onto the primary_controller to execute the task. If it is outside of the threshold, this controller will rotate the robot in place towards that path heading. Once it is within the tolerance, it will then pass off control-execution from this rotation shim controller onto the primary controller plugin. At this point, the robot’s main plugin will take control for a smooth hand off into the task.

The RotationShimController is most suitable for:

  • Robots that can rotate in place, such as differential and omnidirectional robots.

  • Preference to rotate in place when starting to track a new path that is at a significantly different heading than the robot’s current heading – or when tuning your controller for its task makes tight rotations difficult.

  • Using planners that are non-kinematically feasible, such as NavFn, Theta*, or Smac 2D (Feasible planners such as Smac Hybrid-A* and State Lattice will start search from the robot’s actual starting heading, requiring no rotation since their paths are guaranteed drivable by physical constraints).

See the package’s README for more complete information.

Rotation Shim Controller Parameters

angular_dist_threshold

Type

Default

double

0.785

Description

Maximum angular distance, in radians, away from the path heading to trigger rotation until within.

forward_sampling_distance

Type

Default

double

0.5

Description

Forward distance, in meters, along path to select a sampling point to use to approximate path heading

rotate_to_heading_angular_vel

Type

Default

double

1.8

Description

Angular rotational velocity, in rad/s, to rotate to the path heading

primary_controller

Type

Default

string

N/A

Description

Internal controller plugin to use for actual control behavior after rotating to heading

max_angular_accel

Type

Default

double

3.2

Description

Maximum angular acceleration for rotation to heading (rad/s/s)

simulate_ahead_time

Type

Default

double

1.0

Description

Time in seconds to forward simulate a rotation command to check for collisions. If a collision is found, forwards control back to the primary controller plugin.

Example

controller_server:
  ros__parameters:
    use_sim_time: True
    controller_frequency: 20.0
    min_x_velocity_threshold: 0.001
    min_y_velocity_threshold: 0.5
    min_theta_velocity_threshold: 0.001
    progress_checker_plugin: "progress_checker"
    goal_checker_plugins: "goal_checker"
    controller_plugins: ["FollowPath"]

    progress_checker:
      plugin: "nav2_controller::SimpleProgressChecker"
      required_movement_radius: 0.5
      movement_time_allowance: 10.0
    goal_checker:
      plugin: "nav2_controller::SimpleGoalChecker"
      xy_goal_tolerance: 0.25
      yaw_goal_tolerance: 0.25
      stateful: True
    FollowPath:
      plugin: "nav2_rotation_shim_controller::RotationShimController"
      primary_controller: "nav2_regulated_pure_pursuit_controller::RegulatedPurePursuitController"
      angular_dist_threshold: 0.785
      forward_sampling_distance: 0.5
      rotate_to_heading_angular_vel: 1.8
      max_angular_accel: 3.2
      simulate_ahead_time: 1.0

      # Primary controller params can be placed here below
      # ...