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.

See the package’s README for more information.

Velocity Smoother Parameters¶

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.

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