Glossary

Actuator

A physical device that produces motion. In this course, the Dynamixel AX-12A rotates the lamp head. Referenced as an abstraction, not a register bank.

Capability

A semantic operation a consumer can request (for example nod), independent of how it is realized. Consumers request capabilities; implementations choose the realization.

Digital twin

A Pico-based representation of the logical actuator and its state — distinct from merely mirroring a hardware register. Holds desired state and observed state.

Desired state

What the system has been asked to be (for example desiredPosition).

Observed state

What the system reports it currently is (for example actualPosition).

Edge adapter

Hardware/software that sits at the boundary between Open Engineering semantics and a device protocol. The ESP32 is the edge adapter in this course: it speaks actuator-level commands to the AX-12A and never character meaning.

Home Assistant

A home automation platform used here strictly as a human control surface. It requests capabilities (nod, center, stop); it does not own the actuator behavior or implement a servo trajectory.

Control surface

The Open Engineering term for an interface that lets a human (or another actor) express intent, without becoming the runtime or the ontology owner.

Pico

The Open Engineering abstraction for a declarative, composable digital entity described by Rules and produced by a Parser and a Composer. In this course a Pico represents the logical head-pitch actuator.

Manifold

The Pico runtime execution environment: a Kubernetes-hosted RuntimeEnvironment that hosts a Pico Element and executes its rules when events arrive.

Crossplane

Declarative composition for the control plane. In this course it composes the resources needed to realize the requested actuator capability — what should exist.

Open Engineering event

A semantic message that represents something happening in the system, carried below the semantic layer by a transport (for example MQTT). A nod request becomes an event such as pixstars.head.nod.requested.

Correlation identifier

A unique identifier attached to every request so one nod can be followed through Home Assistant → event → Pico → rule → command → edge → servo → completion → telemetry.

Nod

The first, mandatory gesture. A deterministic motion sequence: center → slightly down → slightly up → return to center. Exact safe servo positions are configurable and calibrated, never hard-coded into generic definitions.

Simulation-before-physics

The principle that every capability should be testable without hardware. The SimulatedActuator and DynamixelAX12AActuator implement the same contract.

Safe limits

Configurable minimum/maximum positions, movement speed, timeout, emergency stop, and safe startup/shutdown states within which all physical movement must operate.