Real-Time Physics Simulation Forum

Problem solved. The problem was with the contact manifold and this was masked in the small timestep I was using. After drawing the manifold and outputting some data, the simulation is near perfect. I can now use 100 iterations on 6 bodies without slowing my frame rate due to the handling of the fixe...

Thanks Dirk. I didn't use constraints to derive the impulses, but I think I will give that a go now since regular impulses don't seem to be adequate in my varied timestep. I derive the impulse as follows based on the coefficient of restitution equation: e = vba' / vab Rel vel in the direction of the...

Thanks Dirk. I have gone through the Box2D code and I couldn't find where the variable timestep was used, only for profiling. In the manual, it says that it uses a fixed timestep of 60Hz. Box2D lite is also too fast on my PC and this is not realistic when I load a terrain, perform collisions, which ...

Hi, I am trying to support a variable timestep as follows since I am having problems when loading terrains, which slow the frame rate and fixing this to 60Hz is no longer adequate. I fix the timestep to less than 0.005f and the simulation is stable when stacking boxes. When I raise this further, the...

Hi, I have a terrain partitioned into a quadtree and the rendering is fast, but collision detection for physics is slow. I am trying to test an OBB against the terrain as follows: Basically, if the node is in the viewing frustum, and we are at the leaf node, I check if the OBB is above that visible ...

Thanks Dirk. I have the original line constraint working without limits, however I have a question about the behaviour. Say that body 2 is at the anchor point and body 1 is the fixed body that the line moves with. Is the anchor point supposed to move with body 2 and that r2 stays fixed while r1 chan...

Hi all,

What is the best way to impose a limit on a line constraint? Currently, I have a distance constraint running alongside it but don't know if that's the best way. Should I add another Jacobian and combine it with the line joint?

Thanks for your help

Thanks a lot Dirk. I transformed my tangent axes with the frame they vary with and it still works both ways, regardless of our Jacobians being different, it was a good mistake on my part to learn from.

Thanks for the tips on quaternion constraints, you are most helpful.

The way I understood it is, since the impulse is applied almost instantly, there is no need to integrate the force over time and assume it occurs instantaneously, therefore making P=JT*lambda rather than JT*lambda*h. Is this a correct assumption or should I multiply by the timestep regardless? I hav...

Thanks Dirk! That makes alot more sense The way I am following your process is as follows: dC1/dt = u2.w1 dC1/dt = u2.d/dt(w1) + d(u2)/dt.w1 (Product rule) dC1/dt = u2.Cross(omegaB, w1) + Cross(omegaA, u2).w1 (Since w1 varies with frame B and u2 changes wrt to frame A) dC1/dt = omegaB.Cross(w1, u2) ...

Talking to myself here again ... I have managed to implement the hinge joint properly and test it with success. Also, chain of 3 bodies connected with revolute joints works well. I am now trying to test the following and am having erratic velocities: Body1 is anchored to an immovable body3 using a r...

I have built a hinge constraint with a 5x5 K matrix. My problem is when the bodies rotate about a constrained axis, the solver blows up. If I initialise the constraint to allow rotation about the Z axis of body1, it works fine provided that the bodies do not have a velocity about the other two axes....

Hi, I have managed to implement a Gauss-Jordan elimination function and tested it in inverting a 6x6 matrix successfully. It's a lot faster than cofactors (which I wasted time on) and hopefully it'll help anyone who needs it and save you a lot of pain when dealing with 5 and 6 D.O.F constraint block...

Hi, I am having trouble implementing this restricted angle inequality constraint about an arbitrary axis. I am imposing a revolute joint constraint separately to this, to form a hinge constraint The procedure I am following is shown in the code below: 1) Convert the restricted axis to local coords 2...

That's cool, I did it in Matlab and it's a 32MB file, so it's much simpler to just apply two constraints to a point separately.