chenlin/Mujoco_WASM
1
0
Fork 0
Code Issues Pull Requests Actions 10 Packages Projects Releases Wiki Activity

Add geom adhesion: contacts that pull, via translated friction cones.

Browse Source 
https://youtu.be/GioWwB36XHI

The new geom attribute adhesion (units of force, signed; pair-level
override) translates the contact friction cone along its normal so
that the force origin lies strictly inside it. Consequences: each
contact can pull with up to the given force before breaking, and the
tangential friction budget becomes mu*(f_N + adhesion) -- the
Mohr-Coulomb yield condition with cohesion c = mu*adhesion -- so
lightly-squeezed grasps retain a guaranteed friction floor.

A translated cone factors exactly into {constant attractive force}
+ {original cone}, so no solver kernels change. The implementation is
this factorization: a constant attraction along contact normals
accumulated into the new mjData.qfrc_adhesion (summed into
qfrc_passive), plus a bias of adhesive contact rows' reference
acceleration (aref += R*adhesion), which makes resting penetration
exactly independent of adhesion. Contacts of adhesive pairs remain
active throughout the gap zone, producing rows with positive violation
whose reference acceleration pulls: a tether that resists pull-off
smoothly, captures objects released within the band into steady
contact, and detaches at the specified force. Adhesion values of the
two geoms combine by sum; explicit pairs override.

mj_contactForce reports the net interface force (cone force minus the
adhesive pull), whose normal component can now be negative. Negative
adhesion is allowed and produces a repulsive offset (air hockey).

PiperOrigin-RevId: 950858148
Change-Id: I879c08eba7ae501e5c0f8c2f807167344da4c2bc
This commit is contained in:
Yuval Tassa
2026-07-20 08:35:17 -07:00
committed by Copybara-Service
parent b942c9f922
commit a264d0bc8b
28 changed files with 784 additions and 50 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/engine/engine_setconst.c
+15
View File
@@ -223,6 +223,21 @@ static void setFixed(mjModel* m, mjData* d) {
}
m->flg_surfacevel = flg_surfacevel;
// compute flg_adhesion: whether any geom or pair has nonzero adhesion
mjtBool flg_adhesion = 0;
for (int i=0; i < m->ngeom; i++) {
if (m->geom_adhesion[i]) {
flg_adhesion = 1;
break;
}
}
for (int i=0; i < m->npair && !flg_adhesion; i++) {
if (m->pair_adhesion[i]) {
flg_adhesion = 1;
}
}
m->flg_adhesion = flg_adhesion;
// set jnt_actuatorid and tendon_actuatorid
mju_fillInt(m->jnt_actuatorid, -1, m->njnt);
mju_fillInt(m->tendon_actuatorid, -1, m->ntendon);