Server Example: Cloth on a Slope

Overview

A 1 kg box stands on a cloth on each of two ramps, with a friction coefficient of 0.5 everywhere. The ground holds the cloth under the box with the friction of the box's weight, so on the 18 degree ramp, below the friction angle (tan 18° = 0.32 < 0.5), the cloth and the box stay where they landed. On the 30 degree ramp (tan 30° = 0.58) they slide down together. The cloth is solved together with the box and the ramps (World::setMonolithicDeformables()). Every four seconds the world starts over, and the example prints how far each box moved between 0.5 s and 1.5 s.

Ramp	Default coupling	Solved together
18 degrees: box travel	74 mm	0.001 mm
30 degrees: box travel (Coulomb friction: 0.66 m)	1.26 m	1.12 m

In the default coupling the ground holds each particle with the friction of its own weight only, so the box drags the cloth down the gentle ramp.

Target

CMake target: cloth_on_slope.

Run

./build-examples/examples/cloth_on_slope

Connect rayrai_tcp_viewer to port 8080. On Windows, run build-examples/bin/cloth_on_slope.exe.

Details

• The ramps are static boxes tilted about the y axis; each cloth is a 0.48 m square of 25 x 25 particles weighing 0.15 kg, laid on the upper part of its ramp, with the box on its middle.
• On the steep ramp the box and the cloth slide faster than Coulomb friction allows; see the known limitations in Deformable Objects.
• The scene lives in include/cloth_on_slope.hpp.