Search found 96 matches

by ejtttje
Thu Aug 06, 2009 2:30 pm
Forum: General Bullet Physics Support and Feedback
Topic: timesteps
Replies: 3
Views: 5177

Re: timesteps

For objects to settle/balance properly, the simulation needs to move them for the same amount of time in each update cycle ("step"). Otherwise, if you had a variable timestep, if an object is oscillating slightly, it might move further on one side of the oscillation with a larger timestep,...
by ejtttje
Wed Aug 05, 2009 7:27 pm
Forum: General Bullet Physics Support and Feedback
Topic: "Broken" hinge constraint [SOLVED]
Replies: 6
Views: 7177

Re: "Broken" constraint

It's interesting that the sag of each joint only depends on the CoM of the immediately following link, not all attached links on the arm... Actually, I take this back, modifying the weight of the last link affects the sag of all of the links leading up to it. So things seem "sane", it's j...
by ejtttje
Wed Aug 05, 2009 7:12 pm
Forum: General Bullet Physics Support and Feedback
Topic: "Broken" hinge constraint [SOLVED]
Replies: 6
Views: 7177

Re: "Broken" constraint

OK, some more data points: this is directly related to the gravity and center of mass of the immediately following link, but not to the total mass or CoM of subsequent links. So in other words, in the previous screen shots, the CoM of each link was at the hinge, but as I move the CoM out along the l...
by ejtttje
Wed Aug 05, 2009 6:16 pm
Forum: General Bullet Physics Support and Feedback
Topic: servo implementation tips?
Replies: 3
Views: 6143

Re: servo implementation tips?

There are motors implemented in several constraints (6DOF etc), those are recommended over directly applying impulses. Yeah, I've played with that as well. I might switch over to it since it takes the object mass/inertia into account so I don't have to tweak my controller parameters for each object...
by ejtttje
Wed Aug 05, 2009 6:04 pm
Forum: General Bullet Physics Support and Feedback
Topic: "Broken" hinge constraint [SOLVED]
Replies: 6
Views: 7177

"Broken" hinge constraint [SOLVED]

I have a planar arm, i.e. a series of bodies connected with parallel hinge joints. However the middle hinge "breaks" and dangles instead of staying rigid. http://img43.imageshack.us/img43/8726/picture2gac.th.png The masses are 0.2 for each link, the base is mass 0 to keep it in the air. Th...
by ejtttje
Wed Aug 05, 2009 5:37 pm
Forum: General Bullet Physics Support and Feedback
Topic: servo implementation tips?
Replies: 3
Views: 6143

Re: servo implementation tips?

*bump* I'm still interested in a response.
I've gotten things basically working by just using applyTorqueImpulse, but is there a better way? Should there be a version of applyTorquImpulse which takes a location as well as axis?
by ejtttje
Wed Aug 05, 2009 5:26 pm
Forum: General Bullet Physics Support and Feedback
Topic: Direct manipulation of Rigid Bodies
Replies: 3
Views: 4110

Re: Direct manipulation of Rigid Bodies

See also my other recent threads:
http://bulletphysics.com/Bullet/phpBB3/ ... f=9&t=3315
http://bulletphysics.com/Bullet/phpBB3/ ... f=9&t=3895
where I'm also waiting for implementation tips on a similar problems (how best to apply forces in the world)
by ejtttje
Wed Aug 05, 2009 5:23 pm
Forum: General Bullet Physics Support and Feedback
Topic: Direct manipulation of Rigid Bodies
Replies: 3
Views: 4110

Re: Direct manipulation of Rigid Bodies

I think you need to keep Bullet in the loop if you want the objects to interact in a physical way. Think about it in terms of what happens in the "real world" when you grab an object and move it around: you apply more or less force depending how quickly you try to move and the weight of th...
by ejtttje
Wed Aug 05, 2009 5:03 pm
Forum: General Bullet Physics Support and Feedback
Topic: timesteps
Replies: 3
Views: 5177

Re: timesteps

But there is the possibility to set time steps in the class btDiscreteDynamicsWorld with the function stepSimulation(...). 1) What is it used for? Internal step size, so you call periodically based on your graphics framerate (which might be variable) and have the simulation do a number of internal ...
by ejtttje
Wed Aug 05, 2009 4:52 pm
Forum: General Bullet Physics Support and Feedback
Topic: Simulating dominoes
Replies: 1
Views: 3184

Re: Simulating dominoes

I wonder if you look at contiguous chunks of N dominoes, and they're all deactivated, then replace them with a compound shape and a single body. Then if something wakes up the body, replace it with the original individual dominoes. This could even be done recursively, so it will scale well. I'm a ne...
by ejtttje
Sat Aug 01, 2009 12:20 am
Forum: General Bullet Physics Support and Feedback
Topic: servo implementation tips?
Replies: 3
Views: 6143

servo implementation tips?

I want to implement a PID (and/or just proportional) motor controller to simulate the servos on a robot. Looking at how the motor on the hinge constraint is implemented, it seems I should just call applyTorqueImpulse on each of the connected bodies for each simulation step. However, I feel I am miss...
by ejtttje
Fri Jul 31, 2009 6:16 pm
Forum: General Bullet Physics Support and Feedback
Topic: applyForce() / applyCentralForce() ignored in tick callback?
Replies: 7
Views: 11655

Re: applyForce() / applyCentralForce() ignored in tick callback?

So, what is the current advice for what should be called from a dynamics world tic callback? btHingeContraint.h has the following documentation for setMotorTarget: // extra motor API, including ability to set a target rotation (as opposed to angular velocity) // note: setMotorTarget sets angular vel...
by ejtttje
Fri Jul 31, 2009 3:53 pm
Forum: General Bullet Physics Support and Feedback
Topic: btBoxShape collision oddity (with video) [SOLVED]
Replies: 3
Views: 4491

Re: btBoxShape collision oddity (with video) [SOLVED]

For reference of those who come later, related threads: http://www.bulletphysics.com/Bullet/phpBB3/viewtopic.php?f=9&t=1150 http://www.bulletphysics.com/Bullet/phpBB3/viewtopic.php?f=9&t=2428 http://www.bulletphysics.com/Bullet/phpBB3/viewtopic.php?f=9&t=2513 semi-related: http://www.bul...
by ejtttje
Fri Jul 31, 2009 3:42 pm
Forum: General Bullet Physics Support and Feedback
Topic: porting from bullet 2.71 to 2.74: Friction Callback gone
Replies: 14
Views: 17073

Re: porting from bullet 2.71 to 2.74: Friction Callback gone

BTW, "Custom Friction Model" is still mentioned in the user manual, although as reported here, the SetFrictionSolverFunc() that CcdPhysicsDemo (referenced from the manual) depended on has been removed. Might be nice to take a second and remove the outdated code from the demo and give a lit...
by ejtttje
Thu Jul 30, 2009 8:23 pm
Forum: General Bullet Physics Support and Feedback
Topic: btBoxShape collision oddity (with video) [SOLVED]
Replies: 3
Views: 4491

Re: btBoxShape collision oddity (with video)

I have discovered my problem, but I'm not sure *why* it's a problem: I was doing this: dynamicsWorld->addRigidBody(body); body->setWorldTransform(tr); However, if I swap these: body->setWorldTransform(tr); dynamicsWorld->addRigidBody(body); Then everything is happy. The order does not matter if the ...