[ODE] Jitters

[Geoff Carlton]

Oh yeah, the actual problem.. Hmm.

What is the mass?  If its very small then even 0.01x the velocity can be 
too great a force (I've seen this with very small objects).  Try a lower 
value for both linear and angular, and see if it fixes it, (e.g. -0.001).

Judging by the results it looks like the -0.01 is providing way too much 
force and the object is flying in the opposite direction each frame.

Geoff


Tim Rightnour wrote:

>On 08-Nov-2004 Jon Watte wrote:
>  
>
>>Ouch! The problem is that dBodyGetXxxx returns pointers 
>>into the actual data used by ODE. You're slamming the actual 
>>velocity values kept in the bodies when you do the *= !
>>Just stepping into this with the debugger would probably have 
>>shown you this, assuming you're building ODE from source 
>>(which you should be doing).
>>
>>Instead, you can change your code to:
>>
>>  dBodyAddForce( body, v[0]*-0.01, v[1]*-0.01, v[2]*-0.01 );
>>
>>Same for torque.
>>    
>>
>
>So I changed it to:
>
>void apply_damping(dBodyID body) {
>    const dReal *v = dBodyGetLinearVel(body);
>    const dReal *x = dBodyGetAngularVel(body);
>
>    dBodyAddForce(body, v[0]*-0.01, v[1]*-0.01, v[2]*-0.01);
>    dBodyAddTorque(body, x[0]*-0.01, x[1]*-0.01, x[2]*-0.01);
>}
>
>And the exact same problem occurs.  Body instantly shoots off into oblivion.
>
>OLD sword: pos 1200.00 449.90 1300.00 rot: -0.00 90.00 0.00
>NEW sword: pos 1200.00 454.62 1300.00 rot: -0.00 90.00 0.00
>step
>OLD sword: pos 1200.00 454.62 1300.00 rot: -0.00 90.00 0.00
>NEW sword: pos 1200.00 222.80 1300.00 rot: -0.00 90.00 0.00
>step
>OLD sword: pos 1200.00 222.80 1300.00 rot: -0.00 90.00 0.00
>NEW sword: pos 1200.00 11611.92 1300.00 rot: -0.00 90.00 0.00
>step
>OLD sword: pos 1200.00 11611.92 1300.00 rot: -0.00 90.00 0.00
>NEW sword: pos 1200.00 -547925.38 1300.00 rot: -0.00 90.00 0.00
>
>Groundheight is about 390 at this location.  Without the damping, the object
>settles, but jitters forever.  Dropping the stepsize from 0.05 to 0.01 didn't
>help, the object will still jitter for hours.
>
>---
>Tim Rightnour <root at garbled.net>
>NetBSD: Free multi-architecture OS http://www.netbsd.org/
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