[ODE] Detecting sliding during collision

[Jon Watte (ODE)]

Objects that are sliding the the ground have a non-zero velocity at the 
contact point. Objects that stay pinned to the ground have zero velocity 
at the contact point. You can read the velocity of a specific point 
using a convenient ODE dBody accessor function.

However, why penalize this type of gait? You could penalize on amount of 
energy used, to evolve efficient gaits, but penalizing sliding might 
prevent some really interesting gaits from evolving. In general, I 
thought you wanted to only put in parameters that matter (i e, speed,
staiblity, energy consumption) and not try to "guide" the evolution in 
other manners. Else you might as well build the exact gait you want in 
the first place ;-)

Cheers,

			/ h+


Joshua Bongard wrote:
> I'm evolving a walking robot in ODE, and want to penalize gaits that cause
> the legs or body to slide over the ground. Anyone know of any intelligent
> way to do that? I guess I could poll the displacement of objects that are
> in contact with the ground plane on 2 consecutive time steps, and detect
> whether displacement is above a certain threshold, but maybe there's a
> better way?
> 
> Thanks,
> Josh