Before pixels were tracked by a camera, a rubber ball set two tiny mechanisms in motion.
Model notes
Before a camera tracked the desk, a rubber ball set two small mechanisms in motion. This original reconstruction represents a classic two-button optomechanical PS/2 mouse with a rubber ball. It is not a measured replica of a named retail product. Its mechanical basis is the ball cage, the two orthogonal encoders and the spring-loaded pressure roller documented in patent US5670990A. Patent US7791591B2 also describes the optomechanical quadrature arrangement, and US6396479B2 documents the rubber-coated steel ball.
1 · Surface motion becomes rotation
The 22.8 mm rubber-covered ball rolls without slipping in this idealized simulation. Two perpendicular rollers with a 1.62 mm radius touch the ball, and their shafts turn the slotted disks. A third, freely turning acetal roller is spring-loaded against the ball and keeps it in contact with both sensing rollers. For rightward travel dx and forward travel dy, the ball’s incremental rotation vector in world coordinates is (−dy/R, 0, −dx/R), composed with a normalized quaternion. The sensing shafts turn by dx/r and dy/r, so diagonal motion does not force both rollers to the same speed. The mouse stays centered for inspection while the reference grid moves beneath it.
2 · Two optical channels reveal direction
Each modeled disk has 40 real apertures. The two sampling points are offset by a quarter of the slot pitch. The sequence 00 → 10 → 11 → 01 → 00 produces positive counts; the reverse sequence produces negative counts. Four-edge decoding gives 160 counts per shaft revolution, about 399 counts per inch. These are explicit model parameters, not a manufacturer’s specification. The thin colored paths are explanatory overlays: real infrared light is invisible.
3 · Clicks are independent mechanical inputs
The separate ABS button panels flex downward about their rear roots. A post under each panel presses a switch plunger, which moves a simplified contact spring against a stationary contact. Button events do not rotate the ball or produce tracking counts. Switch bounce, snap-through forces, friction, inertia, dust and signal noise are not simulated. The exploded view is a static inspection state; operation is disabled until the mouse is reassembled.
4 · A round connector, not USB
The cable has continuous geometry, molded strain reliefs, four internal conductors and a six-pin mini-DIN plug with a metal shield and a polarizing key. Standard PS/2 mouse communication uses data, clock, ground and +5 V; the other two contacts are unused in a conventional single-device connection. The report readout illustrates the three-byte movement and button report. It is not an electrical host-interface or timing simulator, and the displayed cable route is shortened for a compact scene.
Material fidelity
Distinct procedural finishes represent etched ivory ABS, dark vulcanized rubber, smooth acetal, nickel-plated steel, phosphor bronze, tinned solder, green solder mask over a fiber-reinforced board, epoxy IC packages and PVC insulation. Board lettering, copper traces, solder fillets, resistor bands, capacitor vents, switch cavities, bearing bores and encoder apertures are modeled geometry, not a painted texture. The finishes are authored physically based approximations, not measured material scans, and the circuit routing is illustrative rather than a verified netlist.
Controls
Click the model to capture input; a notice at the top of the model shows that capture is active, and Escape releases it. Drag to orbit, right-drag to pan, and pinch or use the wheel while captured to zoom (Ctrl or ⌘ with the wheel zooms at any time). To move the mouse, drag the motion pad, hold Shift while dragging the model, use the step buttons, or press the arrow keys while the model or the pad has focus. To click, hold L or R, press a button on the model, or hold the Left and Right buttons. Space runs or pauses the demonstration, keys 1 to 4 select Exterior, X-ray, Open and Exploded, and S saves a rendering. The shared Run and Pause controls also run the demonstration.
Model scope
An original reference-scale reconstruction with no-slip kinematics and idealized electronics. The PCB routing, device markings and displayed cable route are illustrative; the counts, signals and reports follow directly from the modeled geometry.
