A black-and-white square pattern a camera can recognise and decode into an ID,
and from which it can work out the pattern's position and orientation. Used in
Module 10.
Base frame
The coordinate system fixed to the arm's base. "Move to X 200, Y 0, Z 150"
usually means in this frame.
Bus
The single two-wire line that links the controller board to every servo in
turn, carrying both power and data. One break silences everything downstream.
A circular move — the tool follows an arc. One of the three motion types in
Module 6.
Degree of freedom (DOF)
One independent way the arm can move. The SO-ARM101 has five, plus the
gripper.
Encoder
The sensor inside a servo that reports its shaft angle. The STS3215's is
12-bit: 4096 counts per revolution, about 0.088° each.
End effector
Whatever is on the end of the arm doing the work — here, the gripper, or a
pencil clamped in it.
Forward kinematics
Joint angles in, tool position out.
Gripper force
How hard the gripper squeezes. Module 5 has you find the band between dropping
the object and crushing it.
HOME pose
The reference posture the arm is put into before calibrating zero positions.
Getting it right is the whole of that calibration.
HSV
Hue, saturation, value — a way of describing colour that separates "which
colour" from "how vivid" and "how bright", which is why colour thresholding is
done in HSV rather than RGB. Module 7.
Inverse kinematics (IK)
Tool position in, joint angles out. Harder than forward kinematics, and what
lets Module 10 aim at a marker.
Joint
One powered axis. Numbered J1 to J6 along the arm.
LIN
A linear move — the tool travels in a straight line, whatever the joints have
to do to achieve it.
Morphology
Erosion and dilation, applied to a binary mask to remove speckle and close
holes. Order matters; Module 7 makes you find out why.
PID
Proportional-integral-derivative control. Three gains that turn "how far off
am I" into "how hard do I correct". Tuned by hand in Module 8.
PTP
Point-to-point — the fastest move from A to B, with no promise about the path
in between.
Repeatability
How closely the arm returns to the same place on repeated attempts. Distinct
from accuracy, which is how close it gets to the place you asked for. Measured
in Module 3.
Servo
A motor with a gearbox, an encoder and a controller in one package, which
takes a target position and holds it.
STS3215
The Feetech bus servo used throughout both supported arms.
Teleoperation
Driving the arm directly — from the keyboard here, or by moving a leader arm
that a follower mirrors.
Tool frame
The coordinate system attached to the end effector. The four-point calibration
in Module 6 is what tells the software where the pencil tip is in it.
Torque enable
Whether a servo is actively holding position. With it off the arm is limp and
can be posed by hand — which is what the Lab does right after connecting.
URDF
Unified Robot Description Format: the file describing the arm's links, joints
and limits. It is what the 3D view renders and what the IK solves against.
Virtual arm
A simulated robot with the same joints and limits as the real one, used when
no hardware is attached.
Web Bluetooth / Web Serial
The browser APIs that let a web page talk to a device. Only Chromium browsers
have them, which is why the Lab needs Chrome.
Workspace
Everywhere the tool can reach. Module 4 has you map yours, including the parts
that are reachable only awkwardly.
