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Contact Joint Summary

There are three DOF in the contact joint. A generic constraint equation is written as

J v = c (1)

The first DOF is in the normal direction. The LHS of Eq. (1) is

where r1 = cp - p1 and r2 = cp - p2. The RHS of Eq. (1) is

c = erp/hâ‹…depth

But c is limited by maxvel, so

if (c > maxvel) c = maxvel

Since cfm is associated with the constraint DOF, a specific cfm can be entered here. There are 3 possible cfm, which are set up by soft_cfm, slip1, and slip2, respectively.

cfm(1) = soft_cfm

The impact has a direct effect on c

pick the larger value between contact and impact

if(c_i > c) c = c_i

The lower and upper bounds are

lo(1) = 0
hi(1) = infinity

The second DOF is the first tangent direction. Let t1 and t2 be the tangent directions to normal n

c = motion1 (so motion1 and motion2 are velocities)
lo(2) = -mu (if mu=0, the friction force is practically set to zero)
hi(2) = mu
cfm(2) = slip1

The LHS of the constraint equation in the second tangent direction is

The RHS of the constraint equation is

c = motion2
lo(3) = -mu2
hi(3) = mu2
cfm(3) = slip2