Skip to content
Sodero Docs
Sodero Docs Sodero Docs

    Articulation

    The Articulation controller drives an articulated robot joint by joint: legged robots, humanoids, grippers, pan-tilt heads, or any set of joints that receives joint targets. Unlike Motion Studio, it uses no arm kinematics (no DH parameters, no Cartesian motions). It bounds and forwards joint targets from an upper controller, such as the Legged locomotion node that runs a walking policy, and it lets you jog and calibrate the joints by hand.

    Item Value
    Node sodero.amc.NAME
    Document .sdda (Stellar Designer)
    Joints 1 to 64, driven by one actuator gateway
    Units rad, rad/s, N·m 
    flowchart TB
    IMU["IMU gateway"] -- imu --> LL["Legged locomotion<br>walking policy"]
    LL -- "joint targets" --> AC["Articulation"]
    AC -- servo_link --> GW["Actuator gateway"]

    1. The Document

    An .sdda document lists the joints and how the gateway's actuators drive them.

    Per joint Meaning
    Name Joint name
    Position min / max Range of motion; targets outside it are refused
    Velocity max Velocity limit; also the reference for the jog speed
    Torque max Torque limit; the controller clamps its total output to it
    Offset (optional) Joint position at actuator position zero
    Kp, Kd (optional) Stiffness and damping, for PD torque control

    Drive mode. In position mode the controller bounds the joint targets and the drive (or the simulated joint) follows them with its own position control. In pd_torque mode the controller computes a PD torque from Kp and Kd and sends torque commands.

    Actuator mapping. As for manipulators, influence factors connect actuators to joints; one actuator can move several joints and several actuators can move one joint, as long as the mapping is invertible.

    Watchdogs. The controller switches the servo off and latches a stop when the gateway's feedback is older than 100 ms or when no new target arrives for 200 ms (the defaults). Click Clear stop, then Servo on. Reconnecting never switches the servo on by itself.

    2. Open the Articulation UI

    Start the gateway and the Articulation node, then click Articulation in the node's CONTROL section.

    Area Contents
    Left rail Joints (joint monitor), Constraints (configured limits), Set origin
    Top bar Servo on, Servo off, Stop (switches the servo off and latches a stop), Clear stop (releases it while the servo is off), the control mode, and the button that opens the Joint control panel
    Status strip Servo On/Off, Feedback age in milliseconds, Safety (Ready or the reason for a stop)
    Controller The Articulation node this window controls
    Joint monitor Per joint: position, velocity, effort and target

    Stop the upper controller first. Pause or stop Legged locomotion (or any program that sends joint targets) before you jog or calibrate by hand.

    3. Jog Joints

    1. Open the Joint control panel (button at the right of the top bar).
    2. Click Servo on.
    3. Under Joint jog, set the Speed (1–100 % of each joint's velocity limit; 10 % by default).
    4. Hold − or + next to a joint. The joint moves while you hold the button and holds its position when you release it. A jog button also switches the servo on if it is off.

    Leaving the window, switching to another tab or losing the connection switches the servo off.

    4. Send Joint Targets

    Under Joint targets:

    1. Click Use measured positions to copy the current positions into the target fields.
    2. Change the targets of the joints you want to move.
    3. Click Stream targets. The controller follows the targets while the stream runs; Stop target stream ends it and switches the servo off.

    5. Set the Origin

    Set origin assigns an angle to the current position of a joint, for example after an encoder was replaced:

    1. Bring the joint to a known position.
    2. Choose the joint, then click Reset current angle to 0, or enter the true angle (deg or rad) and click Set current angle.

    The servo switches off first; the joint does not move. Afterwards the servo stays off and a stop is latched: check the joint monitor, click Clear stop, then Servo on.

    Some devices only support setting the origin to zero, and robots in simulation do not support it.

    6. Control from Programs

    From How
    A walking robot The Legged locomotion node runs a walking policy and sends joint targets to this node
    The SSH workspace sodero tools call articulation.get_status, articulation.get_joint_state, articulation.servo_on, articulation.uc_pos, articulation.stop (sodero CLI); sodero articulations get shows the joints and actuators
    A module on the Station A module node connected to the Articulation node (Create Custom Modules)