Angular Velocity 2 questions

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The Igors
Posts: 4
Joined: Sat Jul 31, 2010 10:30 am

Angular Velocity 2 questions

Post by The Igors » Mon Mar 21, 2011 2:46 pm

Hi All

I want to specify an initial angular velocity for some bodies before to start simulation. If I set a rotation around single axis, it works fine. But I can't figure out how it works for 2/3 axes. I have created cones along x, y, z and tried to find rotation order experimentally - but nothing does work. For example rotation angles (0, 1, 1 radians) do NOT produce same result as (0, 0, 1) for cone along Y. So

1) What rotation order (in Euler angles) should I specify for angular velocity?

2) How can I specify angular velocity in local space? For example there are 2 bodies: cube (parent) and cone (child). Parent cube is rotated and child cone inherits this rotation. How to applt cube's btTransform to cone's angles?


Posts: 23
Joined: Wed Mar 12, 2008 9:08 am

Re: Angular Velocity 2 questions

Post by h4tt3n » Thu Mar 31, 2011 9:21 am

In the real world, a unconstrained body not influenced by any forces can only rotate along one axis. Look at the Earth as an example. If Bullet allowed you to make an object rotate about more than one axis at a time, it wouldn't be physically correct.


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Joined: Thu Nov 17, 2011 6:32 pm

Re: Angular Velocity 2 questions

Post by hkyriazi » Sat Jan 14, 2012 4:26 pm

In Blender, at least, I think there are options for using local coordinates rather than world ones. And, are you sure you're not confusing rotation (changing the object's orientation) with rotation velocity? The first responder was correct that an object can have only one axis of rotation. Why would you expect that, say, (1,0,0) would give you the same axis as (1,1,0) (unless you think you've got an object angled/tilted between two of the axes, and one is using local coordinates)?

In Blender, at least, one sets the angular velocity in the "logic editor" menu's motion actuator area.

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