Search found 711 matches

by drleviathan
Tue Mar 09, 2021 10:58 pm
Forum: General Bullet Physics Support and Feedback
Topic: Hinge vehicle balance
Replies: 3
Views: 1805

Re: Hinge vehicle balance

Car race-em games often require very tuned "game physics" (as opposed to "accurate physics") in order to make them fun. The example for this I usually give is: crashes. Accurate car crashes happen quite fast: you're in control when suddenly the vehicle is tumbling faster than you...
by drleviathan
Wed Mar 03, 2021 4:17 pm
Forum: General Bullet Physics Support and Feedback
Topic: [HELP] Explosiveness and stretching of physical object connections
Replies: 3
Views: 1687

Re: [HELP] Explosiveness and stretching of physical object connections

Because of bug, sword when attached to hand was always falling, increasing it's velocity higher and higher so everything it touches would fly away. Sword was separate object that was moving as their own as attachment to hand bone, so it wasn't physical movement. Ah I see: you were slamming the swor...
by drleviathan
Wed Mar 03, 2021 3:02 pm
Forum: General Bullet Physics Support and Feedback
Topic: [HELP] Explosiveness and stretching of physical object connections
Replies: 3
Views: 1687

Re: [HELP] Explosiveness and stretching of physical object connections

I watched the video. I believe what is happening is: the objects get into a state of interpenetration and the penetration resolution logic separates them but does so in a non-physical way. The penetration resolution logic is pretty good at getting the objects out of overlap while not pumping too muc...
by drleviathan
Tue Feb 23, 2021 11:12 pm
Forum: General Bullet Physics Support and Feedback
Topic: rotation format in bullet physics
Replies: 5
Views: 1960

Re: rotation format in bullet physics

is there a way to efficiently integrate the rotation with this vector? Do you mean: "Given some initial rotation Q0 and a non-zero angular velocity W ... is it possible to compute the rotation Q(t) as time progresses forward?" If so then: yes. In fact, that is what Bullet does: RigidBody ...
by drleviathan
Tue Feb 23, 2021 7:03 pm
Forum: General Bullet Physics Support and Feedback
Topic: rotation format in bullet physics
Replies: 5
Views: 1960

Re: rotation format in bullet physics

AngularVelocity is indeed a btVector3, however its units are radians/second. It represents the rate of change of the rotation... not the rotation. Perhaps you had a question about AngularVelocity?
by drleviathan
Tue Feb 23, 2021 4:53 pm
Forum: General Bullet Physics Support and Feedback
Topic: rotation format in bullet physics
Replies: 5
Views: 1960

Re: rotation format in bullet physics

Bullet stores both position and rotation in a btTransform which is a 4x4 matrix under the hood. You can extract just the rotation part into a normalized btQuaternion which is a 4D "vector". The components of a Quaternion are NOT the normalized_axis + angle, however with some practice you c...
by drleviathan
Thu Feb 18, 2021 7:48 pm
Forum: General Bullet Physics Support and Feedback
Topic: Food Simulation
Replies: 7
Views: 2324

Re: Food Simulation

I'm guessing your container walls are thin, and the scoop part of your spoon might also be relatively thin. Thin convex parts of a btCompoundShape could very well penetrate with those of another. A likely simple solution would be to change your container model to have thick walls: at least twice as ...
by drleviathan
Wed Feb 17, 2021 9:04 pm
Forum: General Bullet Physics Support and Feedback
Topic: Food Simulation
Replies: 7
Views: 2324

Re: Food Simulation

I would expect hacd to use btCompoundShape under the hood. Maybe try also using hacd on the container.
by drleviathan
Wed Feb 17, 2021 5:55 am
Forum: General Bullet Physics Support and Feedback
Topic: Food Simulation
Replies: 7
Views: 2324

Re: Food Simulation

Bullet is tuned for meters and seconds. There are hard-coded thresholds in the details of shapes and collisions which makes Bullet not work well for tiny objects. However, you could "pretend" Bullet's units are centimeters instead of meters, and thereby simulate smaller physics. So a 0.01m...
by drleviathan
Tue Feb 16, 2021 6:39 am
Forum: General Bullet Physics Support and Feedback
Topic: Food Simulation
Replies: 7
Views: 2324

Re: Food Simulation

To avoid tunneling of convex grains through a concave container in Bullet you should use btCompoundShape (collection of convex sub-shapes) for the container rather than a convex mesh shape like btBvhTriangleMeshShape . The penetration resolution logic works much better for convex-vs-convex than conv...
by drleviathan
Sun Feb 14, 2021 8:47 pm
Forum: General Bullet Physics Support and Feedback
Topic: Collisions between static object and rigidbody ignored?
Replies: 5
Views: 1954

Re: Collisions between static object and rigidbody ignored?

Dunno quite what is going wrong but: In the first case: (a) World gravity is <0,0,0> (b) Both RigidBodies are dynamic (non-zero mass) (c) It looks to me like you create the two objects in an overlapping state so penetration resolution pushes them apart and one moves up while the other moves down. In...
by drleviathan
Fri Feb 12, 2021 2:55 pm
Forum: General Bullet Physics Support and Feedback
Topic: The wire stretched out very long,how to control it!Help! PLS!!!
Replies: 1
Views: 1373

Re: The wire stretched out very long,how to control it!Help! PLS!!!

To summarize your problem (and correct me if I'm wrong): you have a spring constraint that is not stiff enough for your purposes. Weak springs are easy and stiff springs are hard (they can go unstable). Here's some advice without knowing more about what you're really trying to do: (1) Maybe you want...
by drleviathan
Thu Jan 28, 2021 8:02 pm
Forum: General Bullet Physics Support and Feedback
Topic: [Solved]If I want hard constraints is featherstone and multibody the only effective solution?
Replies: 5
Views: 2786

Re: If I want hard constraints is featherstone and multibody the only effective solution?

Years ago (2014) I tried using FixedConstraints (with dynamic transforms) to drive a ragdoll character. I tried a range of numbers of constraints and body-parts. As I recall: with the mass ratios and timesteps I was using: above 15 constraints it was pseudo unstable and with 9 constraints (and fewer...
by drleviathan
Thu Jan 28, 2021 4:49 pm
Forum: General Bullet Physics Support and Feedback
Topic: Simulate the dynamics in large particle systems on which external forces acts with elastic collisions in real time
Replies: 4
Views: 1905

Re: Simulate the dynamics in large particle systems on which external forces acts with elastic collisions in real time

The initial situation would be that there are already 10^4-10^5 particles in the world. Then only single objects (positive and negative charges that are creating the electrical field) are added one after the other. In total, about 10 objects will be added to the world. Will there also be problems i...
by drleviathan
Wed Jan 27, 2021 4:01 pm
Forum: General Bullet Physics Support and Feedback
Topic: Simulate the dynamics in large particle systems on which external forces acts with elastic collisions in real time
Replies: 4
Views: 1905

Re: Simulate the dynamics in large particle systems on which external forces acts with elastic collisions in real time

On a suitable machine I believe Bullet could handle 1e5 rigid spheres. I haven't tried it but this is based on memories of anecdotes I've heard. Dunno about 1e6. Bullet starts to have a measurable performance problem when adding new objects to the world when the number of objects already in the worl...