Velocity Smoother

Source code on Github.

The nav2_velocity_smoother is a package containing a lifecycle-component node for smoothing velocities sent by Nav2 to robot controllers. The aim of this package is to implement velocity, acceleration, and deadband smoothing from Nav2 to reduce wear-and-tear on robot motors and hardware controllers by smoothing out the accelerations/jerky movements that might be present with some local trajectory planners’ control efforts. It can also interpolate velocity commands at higher rates than the controller server publishes.

See the package’s README for more information.

Velocity Smoother Parameters

use_realtime_priority

Type

Default

bool

false

Description

Adds soft real-time priorization to the controller server to better ensure resources to time sensitive portions of the codebase. This will set the controller’s execution thread to a higher priority than the rest of the system (90) to meet scheduling deadlines to have less missed loop rates. To use this feature, you use set the following inside of /etc/security/limits.conf to give userspace access to elevated prioritization permissions: <username> soft rtprio 99 <username> hard rtprio 99

smoothing_frequency

Type

Default

double

20.0

Description

Frequency (Hz) to use the last received velocity command to smooth by velocity, acceleration, and deadband constraints. If set approximately to the rate of your local trajectory planner, it should smooth by acceleration constraints velocity commands. If set much higher, it will interpolate and provide a smooth set of commands to the hardware controller.

scale_velocities

Type

Default

bool

false

Description

Whether or not to adjust other components of velocity proportionally to a component’s required changes due to acceleration limits. This will try to adjust all components to follow the same direction, but still enforces acceleration limits to guarantee compliance, even if it means deviating off commanded trajectory slightly.

feedback

Type

Default

string

“OPEN_LOOP”

Description

Type of feedback to use for the current state of the robot’s velocity. In OPEN_LOOP, it will use the last commanded velocity as the next iteration’s current velocity. When acceleration limits are set appropriately, this is a good assumption. In CLOSED_LOOP, it will use the odometry from the odom topic to estimate the robot’s current speed. In closed loop mode, it is important that the odometry is high rate and low latency, relative to the smoothing frequency.

max_velocity

Type

Default

vector<double>

[0.5, 0.0, 2.5]

Description

Maximum velocities (m/s) in [x, y, theta] axes.

min_velocity

Type

Default

vector<double>

[-0.5, 0.0, -2.5]

Description

Minimum velocities (m/s) in [x, y, theta] axes. This is signed and thus must be negative to reverse. Note: rotational velocities negative direction is a right-hand turn, so this should always be negative regardless of reversing preference.

deadband_velocity

Type

Default

vector<double>

[0.0, 0.0, 0.0]

Description

Minimum velocities (m/s) to send to the robot hardware controllers, to prevent small commands from damaging hardware controllers if that speed cannot be achieved due to stall torque.

velocity_timeout

Type

Default

double

1.0

Description

Timeout (s) after which the velocity smoother will send a zero-ed out Twist command and stop publishing.

max_accel

Type

Default

vector<double>

[2.5, 0.0, 3.2]

Description

Maximum acceleration to apply to each axis [x, y, theta].

max_decel

Type

Default

vector<double>

[-2.5, 0.0, -3.2]

Description

Minimum acceleration to apply to each axis [x, y, theta]. This is signed and thus these should generally all be negative.

odom_topic

Type

Default

string

“odom”

Description

Topic to find robot odometry, if in CLOSED_LOOP operational mode.

odom_duration

Type

Default

double

0.1

Description

Time (s) to buffer odometry commands to estimate the robot speed, if in CLOSED_LOOP operational mode.

enable_stamped_cmd_vel

Type

Default

bool

false

Description

Whether to use geometry_msgs::msg::Twist or geometry_msgs::msg::TwistStamped velocity data. True uses TwistStamped, false uses Twist.

bond_heartbeat_period

Type

Default

double

0.1

Description

The lifecycle node bond mechanism publishing period (on the /bond topic). Disabled if inferior or equal to 0.0.

Example

velocity_smoother:
  ros__parameters:
    smoothing_frequency: 20.0
    scale_velocities: false
    feedback: "OPEN_LOOP"
    max_velocity: [0.5, 0.0, 2.5]
    min_velocity: [-0.5, 0.0, -2.5]
    deadband_velocity: [0.0, 0.0, 0.0]
    velocity_timeout: 1.0
    max_accel: [2.5, 0.0, 3.2]
    max_decel: [-2.5, 0.0, -3.2]
    odom_topic: "odom"
    odom_duration: 0.1
    use_realtime_priority: false
    enable_stamped_cmd_vel: false