Why dose the soft contact lead to the unstable status or sliding when we use the adhesion?

[Aristomo]

Recently, I simulate a strut robot on a ball. This strut will move on the ball and the adhesion actuator is used to add the contact force between them in order to increase the friction force to resist the gravity.

However, the strut is always sliding eventhough I have set the friction coefficient '1'.

I think I have solved this problem after I set the 'noslip_iterations'.

The description in the XML like that:

"This is a post-processing step executed after the main solver. It uses a modified PGS method to suppress slip/drift in friction dimensions resulting from the soft-constraint model."

I am thinking why the soft-constraint model will lead to this situation? This sliding process just likes the error is increasing.