Servo Wall problem

Dear all,

I am using the servo wall model in version 3.3.

I have a bottom wall and a top wall, the particles are between them.

As the first test, I let the bottom wall far away from the particles, and the condition of it is:

mesh/surface/stress/servo meshes/bottom.stl type 1 stress on com 0 0 0 ctrlPV force axis 0 0 1 target_val 10 vel_max 0.01

because there is no contact between the particles and the bottom_wall, I assume the movement of the bottom wall should be:

0.01*time_step*steps
after 10^5 steps, by a time step 10^-9 s, the distance of the bottom should be somehow, 10^-6 m,
but if I looked at the written stl of the bottom, the change was only 9.3e-9 m.

There is a factor about 100 between them.

Has anybody an idea, why this happened?

Thanks a lot!

Zhen