Robot arms

A fixed-base robot is kind: "manipulator", with one arm part per arm. Its part poses are in the robot base frame, and it has no body pose.

A single arm

A Franka Panda with an external and a wrist camera is the end-to-end example in Writing a converter. Its body is one part:

"platform": {
  "kind": "manipulator",
  "embodiment": "franka_panda",
  "parts": [{
    "name": "arm", "type": "arm",
    "joints":   {"signal": "arm_joints", "names": ["j1", "j2", "j3", "j4", "j5", "j6", "j7"]},
    "end_pose": {"channel": "/arm/ee_pose"},
    "grip":     {"signal": "gripper_opening"}
  }]
}

A bimanual station

Two 6-DoF arms with parallel grippers and a force-torque sensor at each wrist, plus three cameras.

overlay.json

{
  "spec_version": "1.1",
  "recording": {
    "id": "station-2-episode-004211",
    "clock": "log_time",
    "t0_ns": 1760000000000000000,
    "task": {
      "instruction": "Fold the shirt in half and place it in the bin.",
      "scene": "A flat shirt on the table, an empty bin to the right."
    },
    "platform": {
      "kind": "manipulator",
      "embodiment": "my_bimanual_station",
      "parts": [
        {"name": "left_arm", "type": "arm", "side": "left",
         "joints":   {"signal": "left_arm_joints", "names": ["j1", "j2", "j3", "j4", "j5", "j6"]},
         "end_pose": {"channel": "/left_arm/ee_pose"},
         "grip":     {"signal": "left_gripper"},
         "force":    {"signal": "left_wrist_wrench"}},
        {"name": "right_arm", "type": "arm", "side": "right",
         "joints":   {"signal": "right_arm_joints", "names": ["j1", "j2", "j3", "j4", "j5", "j6"]},
         "end_pose": {"channel": "/right_arm/ee_pose"},
         "grip":     {"signal": "right_gripper"},
         "force":    {"signal": "right_wrist_wrench"}}
      ]
    }
  },
  "primary_view": "/cam/top",
  "views": [
    {"channel": "/cam/top",         "role": "top",         "label": "Overhead"},
    {"channel": "/cam/left_wrist",  "role": "wrist_left",  "label": "Left wrist"},
    {"channel": "/cam/right_wrist", "role": "wrist_right", "label": "Right wrist"}
  ],
  "signals": [
    {"channel": "/sig/left_arm_joints", "name": "left_arm_joints", "type": "vector", "dim": 6,
     "components": ["j1", "j2", "j3", "j4", "j5", "j6"], "unit": "rad", "rate_hz": 50},
    {"channel": "/sig/right_arm_joints", "name": "right_arm_joints", "type": "vector", "dim": 6,
     "components": ["j1", "j2", "j3", "j4", "j5", "j6"], "unit": "rad", "rate_hz": 50},
    {"channel": "/sig/left_gripper", "name": "left_gripper", "type": "float", "unit": "1", "rate_hz": 50},
    {"channel": "/sig/right_gripper", "name": "right_gripper", "type": "float", "unit": "1", "rate_hz": 50},
    {"channel": "/sig/left_wrist_wrench", "name": "left_wrist_wrench", "type": "vector", "dim": 6,
     "components": ["fx", "fy", "fz", "tx", "ty", "tz"], "rate_hz": 500, "note": "N and N*m, sensor frame"},
    {"channel": "/sig/right_wrist_wrench", "name": "right_wrist_wrench", "type": "vector", "dim": 6,
     "components": ["fx", "fy", "fz", "tx", "ty", "tz"], "rate_hz": 500, "note": "N and N*m, sensor frame"},
    {"channel": "/sig/left_arm_joints_cmd", "name": "left_arm_joints_cmd", "type": "vector", "dim": 6,
     "components": ["j1", "j2", "j3", "j4", "j5", "j6"], "unit": "rad", "rate_hz": 50, "note": "commanded positions"},
    {"channel": "/sig/right_arm_joints_cmd", "name": "right_arm_joints_cmd", "type": "vector", "dim": 6,
     "components": ["j1", "j2", "j3", "j4", "j5", "j6"], "unit": "rad", "rate_hz": 50, "note": "commanded positions"}
  ]
}

Notes

Gripper. grip is the opening as a fraction: 0 = closed, 1 = fully open. Convert from your gripper’s width (divide by its maximum width) or its command range in your converter.
End-effector pose. end_pose is the tool-centre-point pose in the robot base frame. If you log only the end-effector position, publish it as a PoseInFrame with the identity orientation (0, 0, 0, 1) and say so in source.
Two bases. When each arm has its own base, express both arms’ poses in one shared frame (e.g. the left base, or the table), so the two tracks are comparable.
Commanded and measured. joints is the measured state. Commanded positions, velocities and torques are ordinary signals, as left_arm_joints_cmd is here.

Nomadic MCAP Specification

Examples

A single arm

A bimanual station

Notes

​A single arm

​A bimanual station

​Notes

A single arm

A bimanual station

Notes