Presets
Playback
Motion
Automatic raise and lower cycle, or turn auto off and scrub the progress.
Geometry
Where the chain pulls from decides how hard the lift is.
Masses
A tail behind the hinge acts as a counterpoise.
Layers
Model checks
The science
Moment balance about the hinge
With the deck at angle θ the tip is at B = L(cos θ, sin θ), the chain runs to a pulley P and has unit direction u. Quasi-static equilibrium of moments about the hinge: T (B × u) = g cos θ (m c L - Mt Lt), where c L is the centre-of-mass distance and the tail counterpoise Mt at arm Lt helps lift. Hence T = g cos θ (m c L - Mt Lt) / (B × u).
Hinge reaction, winch
R = -(T u + weights). Winch torque is T rdrum; power is T times the chain pay-in speed. The winch work ∫ T dℓ equals the potential-energy gain g sin θ (m c L - Mt Lt), which this page verifies numerically.
Honest simplifications: THORNWARD VI is an original fictional structure; the 3D viewer animates it kinematically and has no physics, so this page supplies a simple rigid-body statics model with plausible masses. One chain stands for the pair, friction, chain weight, wind and inertia are neglected, so the forces are quasi-static estimates. A tail that over-balances makes the tension negative (a chain cannot push): then a brake, not a winch, is needed.
What to try
- Lower the pulley height and watch the tension at a lowered deck explode: the chain pulls almost along the deck.
- Add a tail counterpoise and compare the winch power.
- Pick Overbalanced tail: the tension graph goes below zero.