Controller
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The Controller module is responsible for execution of planned trajectories on the robot. It does this by tracking the trajectory, and thus is sometimes referred to as a trajectory tracker.

Overview

The Controller module receives a time series of robot states, then interpolates to find the desired state to achieve. It generates a control command to achieve this state using the algorithms described below. It is configured to run as fast as or faster than the odometry rate, which is typically set to 50-100Hz.

Currently, the following drive trains are supported:

  • Differential drive

Inputs

  • PoseTree: The library providing the pose frame transform queries

  • Trajectory: The input trajectory to track

  • State: The state estimate to indicate the robot’s current pose

  • Robot remote control: An optional link to the remote controller, so as to only send commands when in Autonomy mode. The robot can operate in three modes: Autonomy, Manual, and Teleoperation.

The controller codelet additionally has algorithmic parameters, which are detailed in the API documentation.

Outputs

  • Command: A tuple of linear and rotational (angular) velocities to drive the robot

Control Algorithms

Currently, the Controller module supports two algorithms: Backstepping Controller and PID Controller.

Backstepping Controller

This is the default controller, which computes errors in the state variables (position, heading) and uses the errors to select commands to drive the robot.

PID Controller

When the use_pid_controller parameter is set to True, the PID controller is enabled and used to track the trajectory while controlling for drift and error.

API Documentation

NvIsaacControllerExtension

Extension containing control operators.

nvidia::isaac::AckermannControlOperator

Generates control messages for an Ackermann base from a trajectory

Parameters:

name

Atlas
lookup_name

atlas
description

Link to ATLAS
flags

GXF_PARAMETER_FLAGS_NONE
type

GXF_PARAMETER_TYPE_HANDLE
default

N/A
name

Allocator
lookup_name

allocator
description

Memory allocator for tensor
flags

GXF_PARAMETER_FLAGS_NONE
type

GXF_PARAMETER_TYPE_HANDLE
default

N/A
name

Command
lookup_name

command
description

Calculated Ackermann base command
flags

GXF_PARAMETER_FLAGS_NONE
type

GXF_PARAMETER_TYPE_HANDLE
default

N/A
name

State
lookup_name

state
description

Robot state from Odometry
flags

GXF_PARAMETER_FLAGS_NONE
type

GXF_PARAMETER_TYPE_HANDLE
default

N/A
name

Trajectory
lookup_name

trajectory
description

Timeseries of Ackermann base states
flags

GXF_PARAMETER_FLAGS_NONE
type

GXF_PARAMETER_TYPE_HANDLE
default

N/A
name

Use PID Controller
lookup_name

use_pid_controller
description

Whether to use the Ackermann PID controller
flags

GXF_PARAMETER_FLAGS_NONE
type

GXF_PARAMETER_TYPE_BOOL
default

N/A
name

PID Controller Baseline
lookup_name

pid_controller_baseline
description

Baseline in meters of the robot, for use in the PID controller
flags

GXF_PARAMETER_FLAGS_NONE
type

GXF_PARAMETER_TYPE_FLOAT64
default

0.5
name

Time Offset to Compensate for Command Delay
lookup_name

command_delay
description

A look-ahead time (in seconds) to get the current command from the received plan in order to compensate delay in execution of the command. Control at current_time + command_delay is sent.
flags

GXF_PARAMETER_FLAGS_NONE
type

GXF_PARAMETER_TYPE_FLOAT64
default

0.0

nvidia::isaac::DifferentialBaseController

Generates control messages for a differential base from a trajectory

Parameters:

name

Sight
lookup_name

sight
description

A sight transmitter handle.
flags

GXF_PARAMETER_FLAGS_OPTIONAL
type

GXF_PARAMETER_TYPE_HANDLE
default

N/A
name

Rebot Remote Control
lookup_name

robot_remote_control
description

Optional link to a RebotRemoteControl, if provided, the controller will only be active if isAutonomyOn is true.
flags

GXF_PARAMETER_FLAGS_OPTIONAL
type

GXF_PARAMETER_TYPE_HANDLE
default

N/A
name

Atlas
lookup_name

atlas
description

Link to ATLAS
flags

GXF_PARAMETER_FLAGS_NONE
type

GXF_PARAMETER_TYPE_HANDLE
default

N/A
name

Allocator
lookup_name

allocator
description

Memory allocator for tensor
flags

GXF_PARAMETER_FLAGS_NONE
type

GXF_PARAMETER_TYPE_HANDLE
default

N/A
name

Output Command
lookup_name

tx_command
description

The command to be executed to follow the trajectory
flags

GXF_PARAMETER_FLAGS_NONE
type

GXF_PARAMETER_TYPE_HANDLE
default

N/A
name

Input State
lookup_name

rx_state
description

Current state of the robot.
flags

GXF_PARAMETER_FLAGS_NONE
type

GXF_PARAMETER_TYPE_HANDLE
default

N/A
name

Input Trajectory
lookup_name

rx_trajectory
description

The trajectory we aim to follow.
flags

GXF_PARAMETER_FLAGS_NONE
type

GXF_PARAMETER_TYPE_HANDLE
default

N/A
name

Estimate Delay
lookup_name

estimate_delay
description

Estimate the delay between the command and its execution automatically. If false the command_delay will be used instead.
flags

GXF_PARAMETER_FLAGS_DYNAMIC
type

GXF_PARAMETER_TYPE_BOOL
default

True
name

Delay Estimation Half Period
lookup_name

delay_estimation_half_period
description

Amount of time accounting for half of the current average.
flags

GXF_PARAMETER_FLAGS_DYNAMIC
type

GXF_PARAMETER_TYPE_FLOAT64
default

1.0
name

Delay Estimation Minimum Score
lookup_name

delay_estimation_minimum_score
description

Minimum score to accept the estimated delay.
flags

GXF_PARAMETER_FLAGS_DYNAMIC
type

GXF_PARAMETER_TYPE_FLOAT64
default

0.98
name

Forward Command
lookup_name

forward_command
description

Simply forward the command from the trajectory
flags

GXF_PARAMETER_FLAGS_DYNAMIC
type

GXF_PARAMETER_TYPE_BOOL
default

True
name

Use PID Controller
lookup_name

use_pid_controller
description

Whether to use the Differential PID controller
flags

GXF_PARAMETER_FLAGS_DYNAMIC
type

GXF_PARAMETER_TYPE_BOOL
default

False
name

Controller Epsilon Gain
lookup_name

controller_epsilon_gain
description

Gain used to compute the forward gain.
flags

GXF_PARAMETER_FLAGS_DYNAMIC
type

GXF_PARAMETER_TYPE_FLOAT64
default

1.0
name

Controller B Gain
lookup_name

controller_b_gain
description

Gain used to compute the heading gain.
flags

GXF_PARAMETER_FLAGS_DYNAMIC
type

GXF_PARAMETER_TYPE_FLOAT64
default

1.0
name

Time Offset to Compensate for Command Delay
lookup_name

command_delay
description

A look-ahead time (in seconds) to get the current command from the received plan in order to compensate delay in execution of the command. Control at current_time + command_delay is sent.
flags

GXF_PARAMETER_FLAGS_DYNAMIC
type

GXF_PARAMETER_TYPE_FLOAT64
default

0.2
name

Forward Error PID parameters
lookup_name

pid_pos_x
description

Parameters of the PID controller for the forward error.
flags

GXF_PARAMETER_FLAGS_DYNAMIC
type

GXF_PARAMETER_TYPE_FLOAT64
default

2.19200247e-316
name

Latteral Error PID parameters
lookup_name

pid_pos_y
description

Parameters of the PID controller for the latteral error.
flags

GXF_PARAMETER_FLAGS_DYNAMIC
type

GXF_PARAMETER_TYPE_FLOAT64
default

3.03143977e-316
name

Heading Error PID parameters
lookup_name

pid_heading
description

Parameters of the PID controller for the heading error.
flags

GXF_PARAMETER_FLAGS_DYNAMIC
type

GXF_PARAMETER_TYPE_FLOAT64
default

2.6381303e-316

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