Zen Fountain: Shishi-Odoshi Tipping-Bucket Simulator (2D)

Fountain Controls

Flow rate 1.0

Filling — water drips into the bamboo tube.

Live Readout

Water volume

Cycle count

Torque balance

Cycle period

– s

How it works

A shishi-odoshi ("deer scarer") is a pivoted length of bamboo, closed off-center so one arm — the mouth — is longer than the tail. At rest the tube is empty and tail-heavy, so it sits tilted with the mouth tipped up, catching a thin stream of water from a spout above.

As water collects in the mouth end, it adds weight at the end of the long arm. Because torque is force × distance from the pivot, even a modest amount of water at the far end of the long arm eventually produces more torque than the short, heavier tail — the classic lever/torque-balance problem. Once the water's torque exceeds the tail's restoring torque, the tube rotates past its tipping point.

Fill phase — volume rises roughly linearly with the flow-rate slider, torque balance creeps toward zero.
Tip & dump — once torque crosses the threshold, the mouth swings down under gravity and the accumulated water empties out in a fraction of a second.
Recoil strike — instantly lighter again, the tube's tail-heavy bias snaps it back past its resting angle, and the tail end raps against a rock — the sharp "gonk" the device is prized for — sending out a visible ripple before settling and refilling.

The volume-vs-time graph below the stage traces this as a sawtooth: a slow linear climb (fill), a near-vertical drop (dump), repeating at a period set entirely by the flow rate — this simulator's 3D counterpart shows the same fountain rendered as a full water-surface mesh instead of this 2D side-view lever diagram.

Water in tube Strike ripple