Feet / wheels slipping even with friction set to 1

[marcimatz]

Hi,

My application allows building random mechanisms and simulating them in various ways, one of them being physically.
The problem that I now encounter is that most mobile mechanisms are slipping more than desired on the ground, even if all friction coefficients are set to 1 and restitution coefficients are set to 0.

The problem becomes more apparent with more complex mechanisms.
Have a look at following few videos:

http://www.youtube.com/watch?v=j2g27zJ3ouk

http://www.youtube.com/watch?v=hng7FG_iGTA

http://www.youtube.com/watch?v=wKyiJEm8PyU

Specially in the case of Aibo, the slipping is quite noticeable. In my understanding it originates because the control of the leg joints (PID control) is always slightly oscillating around the desired target positions, which results in a succession of contact - no contact - contact - no contact - etc. between feet and ground. Am I right in this assumption?

So my question is: how can I avoid having that slipping, or rather how can I increase the "contact maintaining" tolerance to avoid above problem?

I also have to mention that the entire scene is internally scaled up by a factor 10 (adjustable, but it hasn't any influence on the slipping as it seems). Additionally, the floor is a big btBoxShape, the feet are btCompoundShape (that includes btBoxShape and btSphereShape), and the wheels are btCylinderShapeZ.

Thanks for any advice/tip

[ola]

Maybe it won't work, but have you tried to set the friction to some higher value than 1.0? There is no upper limit to the friction value as far as I know.

Cool videos by the way

Cheers,
Ola

[marcimatz]

Thank you Ola,

Yes I tried that, but it didn't make any change.
I really wish I could set some contact maintaining threshold of some sort. Or maybe I could solve that by having a "soft" contact, where colliding objects penetrate each other more that usually? (and so keep the contact state)...

[sparkprime]

there is a contact breaking threshold in bullet, can't remember exactly how to use it or if it applies here, but have a search of the forums if you haven't already

[galileon]

Hey, how did you solve the slipping feet? I have a similar problem: http://www.youtube.com/watch?v=4C5gi_56 ... e=youtu.be

Thanks for any advice