Syplheed-Reborn/docs/re/flight-speed-law.md

The throttle is a TARGET-SPEED selector — measured against the definition (2026-08-13)

Status: ✅ for the shape of the law, 🟡 for the unit scale.

The unit definition gives MinimumVelocity 100, CruisingVelocity 350, MaximumVelocity 1200, Acceleration 600 and Deceleration 500 for UN_f001_TCAF_DeltaSaber_T_Player (values), but not how the game applies them. This measures it.

Method — tools/re-capture/speed_law.py: lock onto the player entity once, then sample its own position triple in guest RAM while holding each throttle input in turn (8 s per phase, 20 Hz). Speed is differentiated over 1-second windows, never per sample.

Result

phase	measured speed (1 s windows)	settles to	definition field
no throttle	367 403 471 365 463 463 365	~420	CruisingVelocity 350
RT held	1041 1376 1551 1379 1596 1510 1620	~1 530	MaximumVelocity 1200
release	1314 672 432 452 432 450 408	back to ~440	—
LT held	203 121 135 121 115 146 122	~125	MinimumVelocity 100
release	369 451 427 425 445 390 465	back to ~430	—

So the throttle selects a target speed — minimum / cruise / maximum — and the craft converges to it; releasing either trigger returns it to cruise. It is not a force model with the throttle adding thrust, which is what a reimplementation would most likely have assumed from Acceleration/Deceleration alone. Those two fields govern the convergence rate: the release phase falls ~1 314 → ~432 in about two seconds (~440 units/s², against Deceleration 500) and the RT phase climbs ~420 → ~1 550 in two to three seconds (~470–560 units/s², against Acceleration 600).

🟡 The unit scale

Measured world-space speeds run ≈1.2–1.3× the definition numbers in all three regimes (cruise 1.21, maximum 1.28, minimum 1.32). The HUD, meanwhile, reads 350 at cruise — the definition value exactly. So the definition's velocity unit is the HUD's, and entity world coordinates are a constant multiple of it, close to 1.25. The spread across regimes is larger than the constant itself is precise, because the craft is manoeuvring under fire while sampled (straight-line displacement per window under-reads a curving path), so this is recorded as a measured range rather than a pinned constant.

Traps

• RT/LT are analogue triggers, so vgamepad trig RT 1.0 holds the throttle; the button verb hold RT is a silent no-op. The first run of this probe measured the drift of a craft nobody was flying.
• Do not differentiate per sample. The guest updates the position slower than 20 Hz, so per-sample differences alternate between 0 and a double step — 0, 1519, 1985, 0, 2681… for a craft flying smoothly.
• Bind late, measure fast. The player entity is not in the typed-entity scan for the first ~15 s of a mission, and the craft dies within a few minutes if nobody is flying it — one earlier attempt ended at GAME OVER mid-probe.

Raw samples: captures/speed-law-throttle-phases.csv.