[ODE] Parameters for evolving *stable* articulated creatures...

[drvdo at free.fr]

Hello, 
 
I'm trying to evolve articulated creatures, Sims-like. 
( http://www.genarts.com/karl/evolved-virtual-creatures.html ) 
 
First I allowed inter-penetration of body parts, and got some good results 
(various types of motion emerged). 
 
Then I decided to make the system more natural: I prevent inter-penetration of 
parts that are not directly connected. That is, a limb and its sub-limb can 
interpenetrate (joint limits are imposed though), but two limbs that are not 
connected together cannot. I thought that only introducing contact between 
non-connected parts would prevent instabilities - silly me :-) 
 
I have tried an awful lot of combinations between ERP and CFM, between 0.005 
and 1. Every single time, the simulation finds a way to obtain a "phantom 
force" behaviour: the organism folds itself, then "hovers" around without any 
body part actually performing any motion (usually with a very small 
"jittering"). 
 
Of course, when I change the ERP/CFM parameters, I can get any creature to 
behave correctly - but then evolution finds a new way to exploit the new 
parameters, and comes up with another "floating" creature. 
 
Frustrating. 
 
If someone has done this kind of things before, I'd like to know how they did 
it ! 
 
Thomas