Robotic Systems · Lecture 12

Unilateral contact, friction, and compliant models

Simeon Nedelchev

Ideal unilateral contact

\phi\ge0,\quad f_n\ge0,\quad\phi f_n=0

A nonadhesive contact pushes without pulling.

Force: N

Impulse: N s

Impact and sustained contact require different interpretations.

\|f_t\|\le\mu f_n

Sliding friction opposes slip.

Sticking permits an interior tangential force.

$v_0=1$ m/s, $\mu=0.2$

d_{\rm stop}=\frac{v_0^2}{2\mu g}\approx0.255\ {\rm m}

The model excludes rolling.

MuJoCo regularizes contact.

Hydroelastic contact uses a distributed pressure model.

Their parameters do not map one-to-one.

Measure penetration, support force, and stopping distance.