Search found 698 matches

by drleviathan
Tue Oct 21, 2014 10:54 pm
Forum: General Bullet Physics Support and Feedback
Topic: Simple question regarding gravity...
Replies: 2
Views: 2619

Re: Simple question regarding gravity...

From my experience Bullet's gravity does accelerate over time. If your framerate is good but your objects are reaching a terminal velocity very quickly then I would guess that the friction from general motion is slowing them down (I bet Bullet has a default "air friction" effect). If this ...
by drleviathan
Fri Oct 17, 2014 10:26 pm
Forum: General Bullet Physics Support and Feedback
Topic: Mesh modification in real time
Replies: 4
Views: 3306

Re: Mesh modification in real time

The shape of an object in Bullet is determined by the pointer btCollisionObject::m_collisionShape and btRigidBody derives from btCollisionObject. When you build a btRigidBody you must pass a shape pointer to the constructor, however the base class btCollisionObject provides an API for swapping the o...
by drleviathan
Fri Oct 17, 2014 10:12 pm
Forum: General Bullet Physics Support and Feedback
Topic: Best setup for motor control algorithm tests
Replies: 8
Views: 5656

Re: Best setup for motor control algorithm tests

I've never used SimBody for my own projects but I did play with some of their demos and poked around their source code. There's one called "JaredsDude" that models a humanoid character from the waist down. It appeared stable and physically correct... more or less. The legs don't actually c...
by drleviathan
Fri Oct 17, 2014 3:17 pm
Forum: General Bullet Physics Support and Feedback
Topic: Bullet for kinematic
Replies: 1
Views: 1994

Re: Bullet for kinematic

No probably not. Bullet doesn't have any IK or even FK utilities. You'd have to find them elsewhere or write them yourself. FK should be relatively easy to write but IK is trickier. If you don't want "physics" then it sounds like you just need visualization. Bullet doesn't even come with i...
by drleviathan
Fri Oct 17, 2014 3:05 pm
Forum: General Bullet Physics Support and Feedback
Topic: Best setup for motor control algorithm tests
Replies: 8
Views: 5656

Re: Best setup for motor control algorithm tests

With the callback function. does that apply to a btMultiBodyDynamicsWorld as well? As far as I can tell this world does not have a setInternalTickCallback method. Yes. btMultiBodyDynamicsWorld derives from btDiscreteDynamicsWorld which derives from btDynamicsWorld which implements setInternalTickCa...
by drleviathan
Thu Oct 16, 2014 11:12 pm
Forum: General Bullet Physics Support and Feedback
Topic: Best setup for motor control algorithm tests
Replies: 8
Views: 5656

Re: Best setup for motor control algorithm tests

I've looked at Bullet's Featherstone demo and implementation. I suspect that it would suit your needs. You might also consider using the SimBody engine: https://simtk.org/home/simbody . Supposedly it has a very stable Featherstone implementation. I doubt its performance would be as fast as Bullet bu...
by drleviathan
Wed Oct 15, 2014 6:39 pm
Forum: General Bullet Physics Support and Feedback
Topic: How to convert relative transform to global transform ?
Replies: 2
Views: 2983

Re: How to convert relative transform to global transform ?

I'm experimenting on something similar: a linked collection of btRigidBody's whose pose is dictated by a set of parent-relative transforms. When I have a new set of parent-relative transforms what I have to do is start at the root of the linked tree and work up. So suppose I had some struct called &...
by drleviathan
Wed Oct 15, 2014 5:47 pm
Forum: General Bullet Physics Support and Feedback
Topic: getInvInertiaTensorWorld() == 0 ??!!
Replies: 2
Views: 2951

Re: getInvInertiaTensorWorld() == 0 ??!!

I was having the same problem here -- btRigidBody::getInvInertiaTensorWorld() would return a matrix of all zeros right after I had set the body's mass properties. After looking at the bullet source code I discovered that the world's inverse inertia tensor is only updated internally when needed (this...