Search found 85 matches

by DannyChapman
Fri May 13, 2011 8:37 am
Forum: General Bullet Physics Support and Feedback
Topic: Set friction doesn't change anything.
Replies: 4
Views: 7417

Re: Set friction doesn't change anything.

The behaviour of rigid bodies _should_ be independent of the overall mass scaling (so if you multiply the masses of all objects by some constant, it shouldn't change the behaviour). Physics engines will probably not be that perfect, but I would have thought would be OK for what you describe (can't b...
by DannyChapman
Thu May 12, 2011 1:13 pm
Forum: General Bullet Physics Support and Feedback
Topic: Box on an inclined plane... friction?
Replies: 2
Views: 2445

Re: Box on an inclined plane... friction?

I have a box on an plane. The plane is inclined by an angle phi. The friction parameter "mu" is set to 0.35 on both of them. Normally the friction coefficient in physics engines is calculated either by a lookup table, or by multiplying a friction parameter on each surface. So, assuming the latter i...
by DannyChapman
Thu Sep 23, 2010 10:36 am
Forum: Applications, Games, Demos or Movies using Bullet
Topic: studioNEST Momentum
Replies: 2
Views: 3003

Re: studioNEST Momentum

Looks like a great integration to me! Hope lots of people find it useful.
by DannyChapman
Thu Aug 12, 2010 10:34 am
Forum: Links, Papers, Libraries, Demos, Movies, Comparisons
Topic: TriplVing's Bullet Vs PhysX Vs ODE performance comparison
Replies: 12
Views: 14250

Re: Bullet Vs PhysX Vs ODE Restitution question

I'm not sure that this is a very fair performance test for the engines! Engines will be optimised for more than one body, and also probably for bodies in contact rather than unconstrained. For example, when I run the PhysX test case I get timings of around 0.07ms, for one sphere falling. However, th...
by DannyChapman
Thu Apr 22, 2010 9:02 am
Forum: General Bullet Physics Support and Feedback
Topic: Low Torque on edge
Replies: 9
Views: 2494

Re: Low Torque on edge

I set gravity 20 instead of 10. Slightly better but still not realistic. If you want to do a direct comparison with your cell phone then you would need to set gravity to around 500. This should result in relative motions being the same (i.e. the same amount of world time to rotate one revolution, o...
by DannyChapman
Tue Mar 16, 2010 10:14 am
Forum: General Bullet Physics Support and Feedback
Topic: Simple newtonian simulations giving wrong results
Replies: 4
Views: 1386

Re: Simple newtonian simulations giving wrong results

Most physics engines optionally add some simple damping to aid stability. I've not checked, but it may be that Bullet has this non-zero by default.
by DannyChapman
Fri Jul 31, 2009 2:29 pm
Forum: General Bullet Physics Support and Feedback
Topic: strange capsule behaviour
Replies: 13
Views: 2876

Re: strange capsule behaviour

It's behaving like this because when a capsule is rolling on its end like in your video, it spins much faster than a cylinder would for the same linear velocity, so it behaves strongly as a gyroscope. Rather than the non-contacting end falling down, the capsule rolls in a circle (to the left in your...
by DannyChapman
Tue Jul 28, 2009 12:06 pm
Forum: General Bullet Physics Support and Feedback
Topic: Jumpy kinematic->dynamic collisions at small timesteps
Replies: 17
Views: 9473

Re: Jumpy kinematic->dynamic collisions at small timesteps

This is a stab in the dark, since I don't use Bullet... but if the solver is aiming to eliminate the penetration error (or some fraction of it) over a fixed number of updates using Baumgarte stabilisation, then a very small timestep will result in large error-correcting velocities because they'll be...
by DannyChapman
Mon May 18, 2009 10:42 am
Forum: General Bullet Physics Support and Feedback
Topic: Doing a 'sphere cast'
Replies: 7
Views: 2751

Re: Doing a 'sphere cast'

If you don't detect overlap between the sphere and the mesh, you want to check if that's because the sphere centre is completely inside the mesh. If your mesh is closed, then you can tell if a point (i.e. the sphere centre) is inside it by doing a ray test in some arbitrary direction. If the number ...
by DannyChapman
Mon May 18, 2009 10:27 am
Forum: General Bullet Physics Support and Feedback
Topic: energy spent for joint motor, difficulty 2.73 --> 2.74
Replies: 5
Views: 2127

Re: energy spent for joint motor, difficulty 2.73 --> 2.74

Can't help with the Bullet-specific stuff, but

Units of impulse = mass * distance / time

Units of energy = mass * distance^2 / time^2

so your calculation (energy = impulse * impulse) must be wrong anyway...
by DannyChapman
Tue Feb 03, 2009 2:15 pm
Forum: General Bullet Physics Support and Feedback
Topic: Problems with bullet 2.73, SSE and std::vector
Replies: 12
Views: 4234

Re: Problems with bullet 2.73, SSE and std::vector

STLport sounds like a good option, though I somehow doubt that it has the same debugging support in Visual Studio as MS STL has, esp. being able to see the size and any entry in a std::vector. You can customise the way types are displayed in Visual Studio by editing: Common7\Packages\Debugger\autoe...
by DannyChapman
Fri Sep 19, 2008 8:55 am
Forum: Applications, Games, Demos or Movies using Bullet
Topic: Natural Motion
Replies: 9
Views: 8487

Re: Natural Motion

Same error as before...
by DannyChapman
Fri Aug 22, 2008 9:04 am
Forum: General Bullet Physics Support and Feedback
Topic: why Bullet demos feel like happening on the moon?
Replies: 16
Views: 5702

Re: why Bullet demos feel like happening on the moon?

i disagree passionately, i mean, if its not VERY, VERY obvious what "visual errors" im talking about then i must assume something is wrong with my computer... 1. It is possible that your computer returns weird timing results (I saw this very occasionally a while back with one or two people having m...
by DannyChapman
Tue Jul 08, 2008 2:22 pm
Forum: General Bullet Physics Support and Feedback
Topic: Force/Impulse timebase
Replies: 29
Views: 27552

Re: Force/Impulse timebase

Other physics SDKs, like Havok and Ageia also clear out the force after the simulation step I think, but I need to verify. Whatever other SDKs do... the idea of clearing the force after each simulation step has never made sense to me for two reasons: 1. The force is quite clearly "owned" by the cli...
by DannyChapman
Wed Jun 25, 2008 10:16 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Flutter and Tumble: The Physics of Falling Paper
Replies: 6
Views: 5372

Re: Flutter and Tumble: The Physics of Falling Paper

One of the soft body demos in Bullet already simulates this, and it's pretty cool.