Real-Time Physics Simulation Forum

Hi ! When combining a revolute joint and an angle constraint to form the 2x2 block K matrix consisting of four 3x3 matrices below for an elbow joint with restricted angular movement, how do I invert this matrix to solve for lambda, which seems like another matrix of two 3x1 vectors as follows: A*lam...

Never mind, was a stupid mistake not to use two anchors. Works perfect now with drift correction.

Hi, I have coded the following distance constraint but am having problems with the bias, since the relative position can sometimes be zero, here is the code, please help ! I have tested it without the bias and it still behaves like a point-to-point constraint Thanks AMG3DDistanceJoint::AMG3DDistance...

Thanks Dirk ! It works great

Sorry, talkin to myself here ... I have got the following equation for JM^-1JT(lambda) = -J*vi for the point-point constraint: (Ma^-1 + skew(ra)*Ia^-1*skew(ra)T + Mb^-1 + skew(rb)*Ib^-1*skew(rb)T)*lambda = (-vai - skew(ra)wai + vb + skew(rb)*wbi) Where vai, wai etc are the initial linear and angular...

Sorry my bad, I forgot to add the entries in JM^-1JT, so it will be a huge multiplication in 3D. None the less, a good way to confirm both methods.

Thanks anyway

Hi, I have followed this process in deriving the jacobian matrix for a point-point constraint: C(x) = xa + ra - xb - rb = 0 where x is the position of each body and r is the distance vector to the anchor point from each body dC/dt = va + cross(wa, ra) - vb - cross(wb, rb) = 0 where w is the angular ...

Anyone have issues with S-H clipping with the Edge-Face case of an OBB? Sometimes, I get 1 contact instead of two, in the middle of a face. void getEdgeFaceClippedContactData(AMG3DPlane clippingPlanes[4], const AMG3DVector4 vSubjectVertices[2], const AMG3DContactID subjectIDs[2], AMG3DContactData *p...

Thanks all. I have taken out the preStep as the normal and tangent masses are required to be calculated at every impulse iteration when using relative velocity, which changes as opposed to Erin's fixed tangent vector. I am getting stable stacking at 10 impulse iterations, but since I have implemente...

Thanks. I have looked it up in Google code but can't find the function body of btPlaneSpace1. Friction should oppose motion, so technically if the relative velocity is pointing down the y axis and the plane normal is pointing up, then the tangent vector should be zero. However this causes a large an...

Hi, I have implemented contact caching for 3D OBB collisions as in Box2D. With the prestep in Box2D, the relative velocity is not used to calculate the tangent vector, instead a scalar is crossed with the contact normal. How do I compute the tangent vector in 3D to put in the prestep function of Box...

Ah yes, my bad, gravity will always act on it since its player controlled. However, if you do put it to sleep and wake it up when you manually apply player forces (with a manual call to a setAwake function), thats 1 idea. Or apply impulses over several iterations if you're using those to resolve col...

How are you making it sleep, are you updating sleep state after updating the position? Perhaps you can play around with the sleep epsilon value if the body keeps moving with low kinetic energy.

Is it necessary to learn this topic to model constraints? I have successfully modelled joints from Erin Catto's presentation (2006). Also, why would you model a penetration/friction constraint when I simply used SAT and normal/tangential impulses with sleeping rigid body state to model stacked boxes...