Longitudinal motion & tyre grip

The tyre force is bounded by a friction circle: Fₓ,max = √((μN)² − Fy²). Rear steering creates lateral demand; braking and drive forces share the available grip. A small rolling resistance and quadratic aerodynamic drag are included.

Suspension & stability

Four independent spring-damper corners use a terrain bump signal. Live tip threshold uses half-track b = 0.62 m and a load-height-dependent combined centre of mass. Roll is estimated from lateral acceleration and cross-slope; it is a warning model, not a certified rollover predictor.

Named rig hierarchy

forklift_root → chassis → front_axle / rear_axle → wheel_fl, wheel_fr, wheel_rl, wheel_rr; chassis → mast_outer → mast_inner → carriage → fork_tilt_pivot → fork_left / fork_right → pallet → cargo_crates

Honest simplifications

• Rigid chassis, planar tyre contact, no wheel lift or full 6-DOF contact solver.
• Torque curve and hydraulic rates are illustrative; transmission, hydraulic pressure, tyre carcass deformation and thermal effects are not solved.
• Payload is treated as one shifted mass; pallet/crate geometry is visual. No collision damage or human operators.
• Fixed integration step 1/120 s; visual rendering interpolates separately.

Replacement assets · GLB URLs intentionally empty

Analytic self-test: run window.__selfTest() in the browser console. It checks slope acceleration, static tip angle and undamped spring period against closed-form values.