[ODE] mass of collisions - imagine a brush

Patrick Enoch Hendrix_ at gmx.net
Fri May 11 07:44:58 MST 2007

Hi Tobias,

this is a little movie I just made. It is a  4x10 array of bristles,  
each bristle is made of 5 capsules. There is no restoring force that  
makes the bristles go straight, so they just fly around. Looks awful  

The settings are:

capsule 1.2 x 0.2 cm, 0.0348 grams
the anchor is in the center of the spherical part of the capsule, the  
capsules overlap in the sperical parts
i used universal links
surface friction 10, bouncyness 10%
gravity -9.81 downwards
erp 80%
cfm 1e-8
delta_t = 200 fps
SOR solver, 100 iterations
max correction velocity 1


The capsules are handled as trimeshes, I havent imported the capsule- 
stuff from the trunk yet.


On 9. May 2007, at 15:43 Uhr, Tobias Zimmer wrote:

> Hi!
> As Remi Ricard wrote, the Universal joint does exactly that! I used it
> to connect the bristles to the head as well.
> But the idea of a restoring torque is really good, I haven't really
> thought about this point yet, but that is very
> important! I guess, this force has to be built into the joint between
> bristle and head especially.
> Thank you for your ideas and fast answers already,
> T.
> Patrick Enoch schrieb:
>> - have all bristles as single geoms, even worse, subdivide the  
>> bristles into several parts connected by universal joints.
>> - the bristles are connected to the head by a ball joint;  
>> preferably a joint that does allow rotation "to the sides", but  
>> not "twisting rotation". I have posted the "free6" joint to the  
>> list (that is capable of this), but the email has not been  
>> approved by a moderator.
>> - the bristles can collide among themselves, ...
>> - but not a single bristle with itself (lets hope they dont bend  
>> too far so self-intersection is possible)
>> - the joints stiffness should be possible via a motor with  
>> rotational velocity of zero and a maxforce (however, this wont  
>> make the bristle return to its original "straight" state)
>> - you need to determine the relative rotation of the subdivided  
>> parts of the bristle (a relative quat), and add a restoring  
>> torque. maybe this should be built into the joint itself.
>> best,
>> Patrick
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