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Universal Robots e-Series and UR-Series

A UR arm streams joint setpoints over RTDE: the two gates every write passes, how a rollout runs.

Here a UR arm streams joint setpoints from Robot("ur5e", mode="real") over RTDE; you learn the two gates every write passes and how a policy rollout runs on it.

This needs the arm's controller reachable on the network, Remote Control enabled on the pendant, and the [ur] extra:

pip install 'strands-robots[ur]'          # ur-rtde: rtde_control + rtde_receive

from strands_robots import Robot

arm = Robot("ur5e", mode="real", driver="strands", port="192.168.1.10")   # URDriver, RTDE on port 30004; a bare call resolves to lerobot
print(arm.connect_eagerly())
print(arm.state())                                        # q, qd, TCP pose, TCP wrench in one round trip
arm.send_action({"shoulder_pan_joint": 0.0, "wrist_3_joint": 1.57})   # radians, servoJ

Joint names and units

Radians, in the order the wire and the MuJoCo assets share: shoulder_pan_joint, shoulder_lift_joint, elbow_joint, wrist_1_joint, wrist_2_joint, wrist_3_joint. A recorded sim action indexes onto the wire unchanged. Every joint travels plus or minus 2 pi (JOINT_LIMIT_RAD).

Two gates on every write

A UR controller does not refuse the way a servo bus does: it accepts the register write and does nothing. So the driver checks before it writes:

  1. Controller mode. connect_eagerly opens the receive interface first because it answers whether commanding is possible. A controller in PROTECTIVE_STOP accepts an RTDE connection and moves nothing, so the driver refuses there and names the mode.
  2. Step size. The commanded step is checked against the model's per-joint maximum speed at control_frequency (default 125 Hz). A step the arm cannot make in one period is refused, not queued.

send_action uses servoJ (speed 0.5, acceleration 0.5, lookahead 0.1 s, gain 300) rather than moveJ, because a policy streams setpoints and a stream of planned trajectories fights itself.

Rollouts

run_policy(policy) rolls a caller-built policy at control_frequency; start_task(instruction, policy_provider=...), which built one in the driver, leaves in 0.8. get_task_status() reports the live snapshot, stop_task() halts the loop; both share the Feetech driver's rollout class.

Deliberately absent

absent why
inverse kinematics, servoL, moveL the action space is joint space, the space the policies here emit
a gripper a UR ships without one; robotiq_2f85 is its own registry entry and driver (Modbus TCP, Robot("robotiq_2f85", mode="real", port="192.168.1.11")), paired by composition
freedrive, URScript upload both take the arm out of the RTDE control mode the driver holds

Simulation

The driver serves ur3e, ur5e, ur7e, ur10e, ur12e, ur16e, ur8long, ur15, ur18, ur20, ur30 (not CB3), each with a MuJoCo twin. Develop action dicts there; drivers explains the shared contract.

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