Search found 74 matches
- Wed Dec 19, 2012 10:51 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Inverse of a block K matrix
- Replies: 2
- Views: 7156
Inverse of a block K matrix
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...
- Tue Dec 18, 2012 11:43 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Distance constraint
- Replies: 1
- Views: 4292
Re: Distance constraint
Never mind, was a stupid mistake not to use two anchors. Works perfect now with drift correction.
- Mon Dec 17, 2012 11:02 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Distance constraint
- Replies: 1
- Views: 4292
Distance constraint
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...
- Sun Dec 16, 2012 3:16 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Point-point constraint
- Replies: 4
- Views: 7785
Re: Point-point constraint
Thanks Dirk ! It works great
- Sat Dec 15, 2012 9:52 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Point-point constraint
- Replies: 4
- Views: 7785
Re: Point-point constraint
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...
- Fri Dec 14, 2012 8:18 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Point-point constraint
- Replies: 4
- Views: 7785
Re: Point-point constraint
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
Thanks anyway
- Fri Dec 14, 2012 4:10 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Point-point constraint
- Replies: 4
- Views: 7785
Point-point constraint
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 ...
- Wed Dec 12, 2012 2:03 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: S-H clipping
- Replies: 0
- Views: 4458
S-H clipping
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...
- Wed Dec 12, 2012 1:52 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Tangent vector
- Replies: 5
- Views: 10835
Re: Tangent vector
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...
- Mon Dec 10, 2012 11:44 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Tangent vector
- Replies: 5
- Views: 10835
Re: Tangent vector
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...
- Mon Dec 10, 2012 12:37 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Tangent vector
- Replies: 5
- Views: 10835
Tangent vector
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...
- Sun Jul 08, 2012 1:13 pm
- Forum: General Bullet Physics Support and Feedback
- Topic: Rigid body not able to stand still
- Replies: 3
- Views: 3667
Re: Rigid body not able to stand still
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...
- Sun Jul 08, 2012 11:52 am
- Forum: General Bullet Physics Support and Feedback
- Topic: Rigid body not able to stand still
- Replies: 3
- Views: 3667
Re: Rigid body not able to stand still
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.
- Sun Jul 08, 2012 11:48 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Lagrange multipliers
- Replies: 8
- Views: 16074
Lagrange multipliers
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...