A skill you write

The smallest skill that does something you can see: open the gripper, then finish. It lives in the project, the way the arm module did.

Create so106/skills.py:

from solarian.core.action import Action, ActionType
from solarian.core.skill import Skill
from solarian.core.execution import ExecutionMode


class OpenGripperSkill(Skill):
    # Runs on the controller's tick. A process would also work; this skill
    # sends one command, so a process is wasted machinery.
    execution_mode = ExecutionMode.INLINE

    def control_step(self, dt):
        self.finish()
        gripper = self.params["gripper"]
        return Action(
            action_type=ActionType.MODULE_ACTION,
            data={
                gripper: {
                    "action_type": ActionType.MOVE_J,
                    "data": {"gripper": {"value": 85.0}},
                },
            },
        )

params is how the skill learns the module's name. It does not hold the module object. 85 is millimetres, fully open, which is the unit UmiSlimFeetechModule already accepts. finish() marks the skill done on the same step it commands the motion. A skill that returned forever would hold the gripper and refuse to be replaced cleanly.

A skill never imports So106Robot. The name "right_gripper" is the whole address. That is what lets the same class run on the controller or on the robot later.

The controller only starts it

Replace so106/controller.py. The joint-nudge control_step has to go. An override of control_step replaces skill ticking, so a skill you start would never get a turn.

from solarian.core import Controller
from solarian.core.event import Event, EventType, event_handler

from so106.skills import OpenGripperSkill


class So106Controller(Controller):
    skills = (OpenGripperSkill,)

    @event_handler(EventType.KEY_DOWN)
    def on_key_down(self, event: Event):
        if event.data["key"] == "o":
            self.start_skill(OpenGripperSkill(params={"gripper": "right_gripper"}))

skills is the list of classes this controller is willing to run. start_skill builds nothing for you: you construct the skill with the params you want, and it stops whatever else is commanding right_gripper.

There is no control_step. The base implementation ticks the running skills and sends what they return.

Try it

Restart the controller and the robot (simulation is fine). Close the fingers in your mind first: they may already be open. Press o.

The fingers should go to fully open and the skill should exit. Press o again and the same thing happens; it does not toggle shut. A key starts. It does not reverse.

The arm no longer nudges. That is the point of deleting control_step. The next chapter puts motion back, as a pose instead of a key-per-joint.

Next: move to a pose.