Search found 96 matches

by ejtttje
Thu Feb 23, 2012 5:50 am
Forum: General Bullet Physics Support and Feedback
Topic: "Sticky" objects
Replies: 1
Views: 1127

"Sticky" objects

We're seeing an issue where objects sometimes stick to our simulated robot. For example, when opening the gripper, the object will cling to one of the fingers a little and be pulled off to the side. Or when pushing an object forward and then backing up, it will pull backward with the robot instead o...
by ejtttje
Thu Oct 20, 2011 2:59 pm
Forum: General Bullet Physics Support and Feedback
Topic: What's going on here? (video)
Replies: 2
Views: 1156

Re: What's going on here? (video)

Sorry, I was getting tired last night and sloppy with the details. For one, I forgot I had also raised the erp, setting that back to default 0.2 seems to make it the most impact here (not entirely fixed though). Experimenting with other parameters since then, the wheel mass was 0.1 and the body mass...
by ejtttje
Thu Oct 20, 2011 5:02 am
Forum: General Bullet Physics Support and Feedback
Topic: What's going on here? (video)
Replies: 2
Views: 1156

What's going on here? (video)

This is a simulation I'm working on. The robot has spinning cylinders on the bottom, pushes it and the box along: http://dl.dropbox.com/u/18503686/JumpySim.mp4 But at various points it looks like the box 'jams' on the ground, makes things occasionally jump. Halfway through the video, it looks like t...
by ejtttje
Fri Sep 16, 2011 7:40 pm
Forum: General Bullet Physics Support and Feedback
Topic: Small object jitter: approaches summary?
Replies: 16
Views: 5830

Re: Small object jitter: approaches summary?

Thanks for all the help so far, I've started integrating what I've learned into my main code. I know you probably want to be done with this topic, but there's still a couple loose ends, bear with me a little longer :) In the attached BasicDemo, I've applied a scaling factor on dimensions, positionin...
by ejtttje
Thu Sep 15, 2011 3:24 am
Forum: General Bullet Physics Support and Feedback
Topic: Small object jitter: approaches summary?
Replies: 16
Views: 5830

Re: Small object jitter: approaches summary?

Thanks for providing that, it looks like it does the trick for quieting boxes. I updated the BasicDemo sample to see how things are going for cylinders and a sphere, and the cylinders have issues with self-rolling. Note this happens on both the ground-box and the ground-plane, regardless of the mult...
by ejtttje
Wed Sep 14, 2011 6:33 pm
Forum: General Bullet Physics Support and Feedback
Topic: Small object jitter: approaches summary?
Replies: 16
Views: 5830

Re: Small object jitter: approaches summary?

Fair enough that it's only a fix for this specific case, but that's better than having a problem in that case instead ;) I do use mostly boxes. Sometimes cylinders as well, and maybe general meshes someday, but we can model a lot with boxes and cylinders (and the occasional sphere for fun). And then...
by ejtttje
Wed Sep 14, 2011 3:27 pm
Forum: General Bullet Physics Support and Feedback
Topic: Small object jitter: approaches summary?
Replies: 16
Views: 5830

Re: Small object jitter: approaches summary?

Or in this case, using a box as the 'ground' also works... I need the CPU to do more than burn extra cycles to work around the physics engine :(
by ejtttje
Sun Sep 04, 2011 6:42 pm
Forum: General Bullet Physics Support and Feedback
Topic: Small object jitter: approaches summary?
Replies: 16
Views: 5830

Re: Small object jitter: approaches summary?

Actually, here's a quick question: I see a lot of jitter when using a btStaticPlaneShape for the ground plane, but oddly switching to a large box is somehow stable. Is that a bug of the plane, or lack of a feature in the box handling?
by ejtttje
Sat Sep 03, 2011 7:45 pm
Forum: General Bullet Physics Support and Feedback
Topic: Small object jitter: approaches summary?
Replies: 16
Views: 5830

Re: Small object jitter: approaches summary?

Further tests reveal this is actually a collection of issues: Object spinning Object drifting Object jitter (e.g. twitching, jumping) Impaled objects Constraint sag Constraint twitch And what you see depends on initial conditions: Spontaneous occurrence vs. only following a drop/impulse Eventually c...
by ejtttje
Fri Sep 02, 2011 9:28 pm
Forum: General Bullet Physics Support and Feedback
Topic: Small object jitter: approaches summary?
Replies: 16
Views: 5830

Re: Small object jitter: approaches summary?

Hmm "only support meters as units" is actually news to me, I've seen a fair bit of discussion regarding scaling the world to get around numerical/stability issues though. The trick is it seems to be scattered and inconsistent, so I'd like to collate some of the items. It may not be "supported" but t...
by ejtttje
Fri Sep 02, 2011 7:37 pm
Forum: General Bullet Physics Support and Feedback
Topic: Small object jitter: approaches summary?
Replies: 16
Views: 5830

Small object jitter: approaches summary?

If I use centimeter units to keep scale of objects in my simulation "around 1", then gravity should be 980. If I use meters as my unit, then my object is 0.05 units on a side, gravity is 9.8, and I still get the jitter. It just seems hard to simulate a small object with accurate gravity. This is sim...
by ejtttje
Fri Sep 02, 2011 6:50 pm
Forum: General Bullet Physics Support and Feedback
Topic: Copying btRigidBody/btCollisionObject? (Physics multiverse?)
Replies: 1
Views: 1585

Re: Copying btRigidBody/btCollisionObject? (Physics multiver

I've gotten a basic version of my program working now. However, there is a small issue: If I simulate a force pushing on a cube for 150 steps, it slides along the ground and picks up a slight rotation. If I do the same thing, but call addRigidBody/removeRigidBody on the cube every step, it picks up ...
by ejtttje
Wed Aug 24, 2011 1:40 am
Forum: General Bullet Physics Support and Feedback
Topic: Copying btRigidBody/btCollisionObject? (Physics multiverse?)
Replies: 1
Views: 1585

Copying btRigidBody/btCollisionObject? (Physics multiverse?)

Just a quick sanity check if you please: I want to do some planning in a physics world, which will involve a lot of saving/restoring physics state to evaluate various possible actions. It seems this will be a fairly straightforward case of having an array of btRigidObjects, copying this array whenev...