Real-Time Physics Simulation Forum

Hi Basroil,

Thanks for your reply. Could you elaborate a bit on the cases under which it might be unstable?

Cheers

I'm experimenting a bit with the multibody and Featherstone solver. Because it is not (afaik) possible yet to apply the btGeneric6DofSpring2Constraint to links, I was wondering if I could emulate spring dampers by simply applying the relevant torque at each timestep. The torque would be proportional...

Hi, I came across this recent paper, which might be interesting for the Bullet community. http://homes.cs.washington.edu/~todorov/papers/ErezICRA15.pdf Simulation Tools for Model-Based Robotics: Comparison of Bullet, Havok, MuJoCo, ODE and PhysX Tom Erez, Yuval Tassa and Emanuel Todorov Abstract— Th...

Hi, I thought this might be helpful for some. Derive from WASDDemoApplication instead of PlatformDemoApplication and WASD keys/arrow keys will allow you to fly through a scene. WASDDemoApplication.h: #ifndef WASD_DEMO_APPLICATION #define WASD_DEMO_APPLICATION #ifdef _WINDOWS #include "Win32Demo...

If width = height = 11, shouldn't your data array contain 11x11 = 121 elements instead of 11?

Hi Erwin,

Thanks for taking the time to look into this. The mass of the kinematic object was set to zero, so that wasn't the source of the problem. The code I posted solved the problem for me.

Looks like the following sequence of code for performing the kinematic update (just before the call to btDynamicsWorld.stepSimulation()) works: m_dynamicsWorld->removeRigidBody(rb); btTransform tr; rb->getMotionState()->getWorldTransform(tr); tr.setRotation(btQuaternion(btVector3(0.f, 0.f, 1.f), btS...

forgot to mention, also played with CFM and ERP, had only a very minor effect on when exactly the instabilities occurred. Also tried calling btGeneric6DofSpring2Constraint->calculateTransforms() after each kinematic move step, no success.

hey, There seems to be an issue with btGeneric6DofSpring2Constraint in combination with rotating one of the bodies to which it is attached. Everything goes well until a certain point, where the non-kinematic sphere starts twitching and then experiences a violent jump. So it seems as if the constrain...

You can also look into btGeneric6DofSpring2Constraint (notice the 2), it uses a completely different implementation of the physics.

thanks for your detailed reply. Unfortunately, the pendulum does not scale right with the given factors: it is much too sluggish. // physical parameters // N.B. [N] = [kg·m/s^2] const float pendulum_length = 5E-3; // [m] const float mass = 1E-3f; // [kg] const float spring_constant = 75E-3; // [N·m/...

Hello all, Some time ago, I implemented a simple damped pendulum simulation to check the physical accuracy of Bullet. The thread is here: http://www.bulletphysics.org/Bullet/phpBB3/viewtopic.php?f=9&t=10184 After making the adjustments mentioned in the thread, accuracy was very good with MKS uni...

Please see this thread for my simulation of a damped pendulum: http://www.bulletphysics.org/Bullet/phpBB3/viewtopic.php?f=9&t=10184 Accuracy was very good in the end, with MKS units. However, world scaling is not yet working (e.g. simulating a very tiny pendulum), am about to launch another thre...

Could angular inertia be the culprit? In the Python case, the pendulum is ideal, with a point mass. In Bullet, the mass is distributed over a rigid body of nonzero size (i.e. the swinging body of the pendulum). For a long enough pendulum and a low enough mass (L = 10 m, m = .1 kg) the results overla...

Sorry, forgot to mention. Basroil, thanks for your suggestions. D6_LIMIT_ERROR_THRESHOLD_FOR_ROTATION makes no apparent difference. I also recompiled everything with double precision floats. Again no evident change.