Glossary

Terms used throughout these docs, explained plainly first, with the technical detail after.

Tendon-driven : A finger design where a motor pulls a string (the "tendon") to curl the finger, instead of a motor sitting inside each joint. Mirrors how your own fingers work: the muscles are in your forearm, and tendons carry the pull down into the finger.

MCP / PIP / DIP joint : Anatomical names for finger joints, used loosely in the code/docs for the tracked landmark points. MCP = knuckle (where finger meets palm), PIP = middle joint, DIP = joint nearest the tip. The thumb only has 2 of these (no true PIP).

Landmark : One tracked (x, y, z) point on the hand, as reported by MediaPipe. 21 per hand: wrist plus 4 per finger.

MediaPipe : Google's machine-learning library used here for hand tracking. Specifically the newer Tasks API (HandLandmarker), not the older mp.solutions.hands API removed in recent versions. See Vision Pipeline.

EMA (exponential moving average) : A simple smoothing technique: each new value is blended with the previous smoothed value by a weight, rather than used raw. Used here to remove frame-to-frame jitter from tracked finger angles before sending them anywhere. See Vision Pipeline.

Serial (protocol) : A simple one-way stream of text over a USB cable, here carrying one line of 5 numbers per video frame from the PC to the Arduino. No acknowledgement, no handshake. See Firmware & Serial Protocol.

Servo (motor) : A small motor that can be commanded to hold a specific angular position (0-180°), rather than just spinning at a speed. Used here, one per finger, to pull the tendon a controlled amount.

Curl fraction : A 0.0-1.0 number representing how curled a finger is (0=straight, 1=fully curled in the simulation's convention), derived from the tracked joint angle. See Vision Pipeline.

URDF / SDF : Text file formats that describe a robot's physical structure: links (rigid parts), joints (how they connect and move), visual meshes, collision shapes, and mass/inertia. URDF is ROS's format; SDF is Gazebo's native format (this project converts URDF → SDF for the hand model).

Mimic joint : A joint constraint that forces one joint to copy another joint's motion (optionally scaled), used here so one motor's commanded position drives all 3 joints of a simulated finger together, matching the real hardware's 1-motor-per-finger design. See Simulation: the mimic-joint gotcha.

Physics engine (dartsim / bullet-featherstone) : The underlying simulator that computes how forces, joints, and collisions actually move objects in Gazebo. Gazebo supports several interchangeable engines; this project uses two different ones for different worlds, because one of them doesn't support a feature (mimic joints) the hand model needs. See Simulation.

Gazebo Transport : Gazebo's internal publish/subscribe messaging system (topics, like ROS topics) used to send joint commands into a running simulation from an external script.

ROS2 (Robot Operating System 2) : A widely-used robotics middleware/framework. This project uses ROS2 Jazzy alongside Gazebo Harmonic, though the hand's own control pipeline (vision → serial/Gazebo bridge) doesn't route through ROS2 topics directly.