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MotionAtelier

Bounce

Bounce makes a value fall onto its target and rebound a set number of times, each rebound lower and shorter than the last, until it comes to rest.

Bounce with default parametersThe value accelerates from 0 to 1, then dips back three times, each dip lower and shorter, before resting at 1.
Bounce, default parameters (Bounces 3, Elasticity 0.50). The dot on the right moves the way the committed channel will. Plotted from MotionAtelier 0.4.2's own curve code, outside Houdini. An illustration of the curve, not a screen capture.

Use it

Section titled “Use it”
  1. Set SHAPE ▸ Bounce.
  2. In the Motion Stack tab, set Bounces and Elasticity. The graph updates as you drag.
  3. Preview it, select the keys in Houdini, and press Commit Keys.

The curve runs from the first key’s value (0) to the second key’s value (1), and every contact lands exactly on the second key’s value. For a drop onto a floor, key the floor height as the second key.

Parameters

Section titled “Parameters”
ControlRangeDefaultWhat it changes
Bounces0 to 123Rebounds after the first contact. 0 gives a single accelerating fall with no rebound.
Elasticity0.05 to 0.950.50Share of impact speed kept by each rebound (coefficient of restitution). Each rebound reaches Elasticity² of the previous height: 0.50 → 25 %, 0.80 → 64 %. Higher values bounce longer.
Bounce with three Elasticity valuesWith Elasticity 0.3 the rebounds are tiny and over quickly; at 0.5 they are moderate; at 0.8 they are tall and take most of the duration.
  • Elasticity 0.30
  • Elasticity 0.50
  • Elasticity 0.80
Bounces 3, with Elasticity 0.30, 0.50 and 0.80. The whole bounce always fills the interval, so livelier bounces make the first fall shorter. Plotted from MotionAtelier 0.4.2's own curve code, outside Houdini. An illustration of the curve, not a screen capture.
Bounce with one and with six reboundsOne rebound gives a single dip after the first contact; six rebounds give a series of shrinking dips.
  • Bounces 1
  • Bounces 6
Elasticity 0.50, with Bounces 1 and 6. Plotted from MotionAtelier 0.4.2's own curve code, outside Houdini. An illustration of the curve, not a screen capture.

Behaviour

Section titled “Behaviour”
  • Physics. The curve is free fall under constant gravity: each flight is a parabola, and Elasticity is the coefficient of restitution. The whole motion is scaled to fit the interval.
  • Exact and sparse. Each half-flight is represented exactly by one Bezier segment, so the committed keys reproduce the physics with no approximation. A bounce uses 2 + 2 × rebounds keys per interval (8 with the defaults).
  • Contacts are broken knots: the velocity reverses instantly. Apexes are smooth with zero slope.
  • Invisible rebounds are left out. A rebound whose peak would be under 0.1 % of the drop height is omitted, and the status line reports … rebounds below visibility: too small to see, left out. Raise Elasticity or lower Bounces to avoid it.
  • Changing a parameter is a local undo step; the scene changes only when you commit.

Factory recipes

Section titled “Factory recipes”
Recipe Bounces Elasticity
Heavy Drop 1 0.30
Soft Landing 3 0.45
Rubber Ball 6 0.65
Long Settle 12 0.80
Section titled “Related”
  • Elastic: overshoot and settle instead of rebound.
  • Motion Stack: add Noise or Lag on top of a bounce.
  • Apply To: one bounce per interval, or one across the whole selection.