ROS 2 adapters

Most people run the bridge node and never see these. Reach for them when you want a ROS 2 node of your own shape.

from videosdk_teleop.adapters.ros2 import ROS2FollowerAdapter, ROS2LeaderAdapter

Neither imports rclpy. You hand them a function to publish through and an object to read from, and they take care of the session, safety and correlation.

ROS2FollowerAdapter

Runs on the machine with the robot.

ROS2FollowerAdapter(meeting_id=None, *, ranges, sink, latest=None,
                    robot_id="ros2", state_timeout_s=0.5, control_hz=100, **kw)

JointRanges

required

How far each joint travels, in your topic’s own units. See below.

callable

required

Called with {joint: value} whenever a command is applied. Publish from it.

object

Where the adapter reads the arm’s current position. Your subscription fills it. Leave it out to run without feedback.

float

default:"0.5"

How old a reading may be before it counts as stale.

int

default:"100"

The loop rate, and the rate announced to the leader.

str

default:"ros2"

A name for this machine, used in logs and recordings.

any

Everything from Follower: token, safety, record and the rest.

ROS2LeaderAdapter

Runs on the machine with the controller. Same ranges and latest, with no sink, since a leader never writes.

ROS2LeaderAdapter(meeting_id=None, *, ranges, latest=None, robot_id="ros2",
                  state_timeout_s=0.5, deadband=0.0, **kw)

float

default:"0.0"

Ignore movements smaller than this, so a controller sitting still does not send noise.

any

Everything from Leader: sync_buffer_ms, max_misalignment and the rest.

Joint ranges

How far each joint travels, in whatever units your topics already carry. This is what turns your values into something the other machine can read, and back.

from videosdk_teleop.adapters.ros2 import JointRanges

ranges = JointRanges.from_lists(
    ("shoulder_pan", "shoulder_lift", "elbow_flex",
     "wrist_flex", "wrist_roll", "gripper"),
    mins=[-1.92, -1.75, -1.69, -1.66, -2.79, -0.17],   # radians
    maxs=[1.92, 1.75, 1.69, 1.66, 2.79, 1.75])

Each machine uses its own arm’s travel, never the other’s, which is what lets two arms of slightly different size drive each other correctly.

On an SO-101 you can read these from the calibration instead of typing them. See SO-101.

Example

A follower node in full. Your subscription hands the arm’s position to the adapter, and the adapter hands commands back to your publisher.

from videosdk_teleop.adapters.ros2 import JointRanges, ROS2FollowerAdapter


class ArmBridge(Node):
    def __init__(self):
        super().__init__("arm_bridge")

        self.latest = Latest()
        self.pub = self.create_publisher(
            JointState, "/follower/joint_commands", 10)
        self.create_subscription(
            JointState, "/follower/joint_states", self.on_state, 10)

        self.adapter = ROS2FollowerAdapter(
            MEETING_ID, ranges=RANGES, latest=self.latest,
            sink=self.send, control_hz=100)

        self.adapter.start()
        self.create_timer(1 / 100, self.adapter.tick)

    def on_state(self, msg):
        """Your driver's feedback, on its way to the adapter."""
        self.latest.put(dict(zip(msg.name, msg.position)))

    def send(self, joints):
        """The adapter's command, on its way to your driver."""
        msg = JointState()
        msg.name = list(joints)
        msg.position = [float(v) for v in joints.values()]
        self.pub.publish(msg)

Your timer drives the loop, so there is no run() here. Latest is a small object of your own with two methods, put(values) and get() -> (values, age_seconds). The runnable example below has one you can copy.

Runnable example

This node in full, about a hundred lines, ready to run.

read_joints() never raises. If the topic goes quiet it falls back to the last value it wrote, so a silent driver cannot take your node down.

Follower

The base class these subclass, and everything they inherit.

ROS 2

The bridge node these two feed, and every parameter it takes.

Python SDK

Adapters

Classes

ROS2FollowerAdapter

ROS2LeaderAdapter

Joint ranges

Example

Runnable example

Follower

ROS 2

​ROS2FollowerAdapter

​ROS2LeaderAdapter

​Joint ranges

​Example

Runnable example

​Related

Follower

ROS 2

ROS2FollowerAdapter

ROS2LeaderAdapter

Joint ranges

Example

Related