Bus

Share data with the rest of the robot through the Robot Bus: publish messages on topics and read them back, call services that robot skills, ARCx and other programs provide, look up where one frame (a camera, the robot's body) is from another, and record topics to play back later. Messages are JSON, so a script publishes dicts and lists and gets dicts and lists back. The same topics and services are open to robot skills, AI assistants and programs outside ARCx (Python, JavaScript, ROS nodes through the ROS Connector), which connect to the robot's Robot Bus address when it is turned on in Options → Preferences → Robot Bus. Views → Robot Bus shows everything on the bus, live.

Bus.Publish("/my_robot/status", {"state": "patrolling", "lap": 3})

pose = Bus.GetLatest("/arcx/nms/pose")

if pose is not None:
  print("At", pose["x"], pose["y"])

heard = Bus.WaitForMessage("/arcx/speech/recognized", 10000)

if heard is not None:
  Bus.Call("/arcx/speech/say", {"text": "You said " + heard["text"]})

camera = Bus.LookupTransform("base_link", "camera")   # [x, y, z, roll, pitch, yaw]

Where to find it: type Bus. in a Python script, or open the ARCx API view of the script editor and expand Bus

Commands

Details

Bus.Call

Calls a service and waits for its answer. Throws when the call fails or the time runs out, so the reason shows in the script console; wrap it in try and except to carry on instead.

Bus.Call(service)
Bus.Call(service, args)
Bus.Call(service, args, timeoutMs)

Gives back: object. What the service returned.

Bus.Exists

Checks whether a topic exists.

Bus.Exists(topic)

Gives back: bool. Whether anyone has published or advertised it.

Bus.GetAge

Gets how many seconds ago the latest message on a topic was published.

Bus.GetAge(topic)

Gives back: float. The age in seconds, or -1 when nothing has been published on the topic.

Bus.GetField

Gets one field of the latest message on a topic by its path, such as x or pose.yaw or objects.0.name.

Bus.GetField(topic, path)

Gives back: object. The field's value, or None when the topic or field does not exist.

Bus.GetFrames

Lists every frame name in the transform tree, sorted.

Bus.GetFrames()

Gives back: list[str]. The frame names.

Bus.GetLatest

Gets the latest message published on a topic, as a dict.

Bus.GetLatest(topic)

Gives back: object. The message data, or None when nothing has been published on the topic.

Bus.GetRate

Gets how many messages per second a topic is receiving right now.

Bus.GetRate(topic)

Gives back: float. The rate in messages per second, or 0 when it is quiet or does not exist.

Bus.GetServices

Lists the names of every service on the bus, sorted, or only those a pattern matches, such as /arcx/recorder/* .

Bus.GetServices()
Bus.GetServices(pattern)

Gives back: list[str]. The service names.

Bus.GetTopics

Lists the names of every topic on the bus, sorted, or only those a pattern matches, such as /arcx/** .

Bus.GetTopics()
Bus.GetTopics(pattern)

Gives back: list[str]. The topic names.

Bus.LookupTransform

Gets where one frame is as seen from another, as [x, y, z, roll, pitch, yaw] in metres and radians. Throws when the frames are not connected.

Bus.LookupTransform(target, sourceFrame)

Gives back: list[float]. The position and rotation of sourceFrame in target.

Bus.Publish

Publishes a message on a topic. Every robot skill, script and external program subscribed to the topic receives it, and it becomes the topic's latest message. Naming the type tells others what fields to expect.

Bus.Publish(topic, data)
Bus.Publish(topic, data, type)

Bus.SetTransform

Sets where a frame is relative to its parent, such as a camera on the robot, and optionally whether it is fixed (bolted down) or moving. Metres and radians, +X forward, +Y left, +Z up.

Bus.SetTransform(parent, child, x, y, z, roll, pitch, yaw)
Bus.SetTransform(parent, child, x, y, z, roll, pitch, yaw, isStatic)

Bus.StartPlayback

Plays a recording back onto the bus with its original timing, or faster or slower.

Bus.StartPlayback(name)
Bus.StartPlayback(name, speed)

Bus.StartRecording

Starts recording topics to a file in ARCx Data\Recordings. Use ** to record everything.

Bus.StartRecording(topics)

Gives back: str. The recording's name.

Bus.StopPlayback

Stops the playback, if one is running.

Bus.StopPlayback()

Bus.StopRecording

Stops the recording being made.

Bus.StopRecording()

Gives back: float. How many messages were recorded, or 0 when nothing was recording.

Bus.TransformPoint

Converts a point from one frame to another, such as an object the camera sees into the robot's frame. Throws when the frames are not connected.

Bus.TransformPoint(target, sourceFrame, x, y, z)

Gives back: list[float]. The point in the target frame as [x, y, z].

Bus.WaitForMessage

Waits for the next message on a topic, with no time limit or until the time limit passes.

Bus.WaitForMessage(topic)
Bus.WaitForMessage(topic, timeoutMs)

Gives back: object. The message data, or None when the time ran out.