ROS 2 examples: a Twist → Zenoh gateway and a turtlesim driven by goals over MCP #421

Context

The Zenoh connector ships the ros2_talker and ros2_listener examples, which the interop test uses. Its README shows how plain Zenoh and ROS 2 can share one session. Two runnable examples should show what AimDB adds next to a ROS 2 system:

1. Observe: a gateway that reads a robot's topic, keeps it as a typed record and republishes it for non-ROS consumers.
2. Command: an LLM, through aimdb-mcp, sets goals; an AimDB controller turns goal + pose into velocity commands. The model says what to do, the controller decides how to move, and ROS 2 actuates.

The second example is the basis for a walkthrough and a blog post.

Part 1: ros2_gateway (Twist → JSON)

• Topic type: geometry_msgs/msg/Twist on /cmd_vel. It is a standard type with nested messages (Vector3) but no header or sequences, so the derive and CDR path carry it today. Type hash (Jazzy and Lyrical): RIHS01_9c45bf16fe0983d80e3cfe750d6835843d265a9a6c46bd2e609fcddde6fb8d2a.
• Flow: ros2://cmd_vel → record robot.cmd_vel → zenoh://telemetry/cmd_vel as JSON, on one Zenoh session. Read-only AimX on a Unix socket for aimdb watch.
• Location: aimdb-zenoh-connector/examples/ros2_gateway.rs, with a small zenoh_sub example so the payload can be read without the Zenoh tools.

Part 2: turtlesim_mcp (goals over MCP)

Claude ──set_record──▶ turtle.goal   {"GoTo": {"x": 8.0, "y": 8.0}} | "Stop"
turtlesim ──/turtle1/pose──▶ turtle.pose
turtle.goal + turtle.pose ──transform_join──▶ turtle.cmd_vel ──▶ /turtle1/cmd_vel

• Records:
  • turtle.goal is an enum with GoTo { x, y } and Stop. It is the only record writable over AimX.
  • turtle.pose is turtlesim's pose, read-only. turtlesim's messages moved packages after Jazzy, so the type name and hash depend on the distro:
    • Jazzy: turtlesim/msg/Pose (RIHS01_739beba26bcba6920404ba722b7b8321348512f92ea5be235c47251940dd8aa9)
    • Lyrical: turtlesim_msgs/msg/Pose (RIHS01_37b07ace09a0ed2c5b774b1410dec972dfd1d292de5656ebc2b075ac646e09c8)
  • turtle.cmd_vel is a Twist produced by the controller, so remote writes to it are refused.
• Controller: a transform_join over goal and pose that runs on every pose. It turns toward the target, drives, and stops within a tolerance. Speeds are clamped in the controller, not trusted from the caller.
• Location: aimdb-zenoh-connector/examples/turtlesim_mcp.rs.

Acceptance criteria

• ros2_gateway: subscribes to Twist over ros2://, stores it as a typed record, and republishes JSON on zenoh://. Both links share one session, and AimX serves the record for aimdb watch.
• turtlesim_mcp: GoTo and Stop set over AimX (aimdb-mcp set_record, or the CLI) move the turtle to the target and stop it there. turtle.cmd_vel and turtle.pose are readable but not writable.
• A walkthrough with a supported ROS 2 distro and rmw_zenoh_cpp. It covers:
  • starting the router,
  • ROS_DOMAIN_ID and ZENOH_ENDPOINT,
  • ros2 topic pub with the expected aimdb watch output and Zenoh JSON payload,
  • turtlesim with aimdb-mcp configured in Claude.
• tests/interop/ros2_interop.sh and its Dockerfile run both examples against real ROS 2, so the walkthrough can't drift:
  • the gateway's republished JSON and its aimdb watch output,
  • a GoTo reaching its target in turtlesim within a tolerance,
  • a refused write to turtle.cmd_vel.
• Both examples are linked from the connector README.

Not in scope

Services and actions (for example turtlesim's RotateAbsolute), path planning, and hardcoded maneuvers. A square is four GoTos sequenced by the caller.

Shared-session setup · Existing talker example · Existing interop test