How to calibrate sphere to plane stiffness and damping values correctly?

2 visualizzazioni (ultimi 30 giorni)
I have been trying to apply contact forces in between my quadruped legs and floor using contact force library by steve miller. floor is modeled using a thin brick and each leg has a small sphere in the end. so i used sphere to plane block for modelling. i used the sphere on table example to get an idea. started calibratng starting from 1e4 and 1e2 as mentioned in the readme.txt file. robot keeps falling thrrough the floor.
so temporarily i made a new model by myself to understand ball on table example further. When i changed the values initially it went up.(upwards from the floor). And at some point it started floating without going up or down. and then when i reduce the values further, it started to fall through the floor.
So this is what i understood,
1) My robot's weight is high. so im gonna need larger initial values for stiffness and damping
2) That floating state means i'm closer to the correct value
So are these correct?
how can i get to the correct value(from floating state)?
i need the ball/robot to fall on the ground and then stay there without going through the floor.
  1 Commento
David Taunton
David Taunton il 2 Gen 2019
Prior to adjusting the contact force, I would suggest that you check all the state targets (prizmatic and revolute) to ensure that you do not have conflicting initial conditions. Also check that that the correct contact force is established at t=0 and that objects in contact have the expected penetration at t=0. I would also check that the priorities of the state targets is what you want.

Accedi per commentare.

Risposte (1)

Steve Miller
Steve Miller il 1 Apr 2019
Hi there,
It is hard to determine from your description what the problem is. Your approach sounds good, but you need to make sure that you are solving the right problem.
First: plot the force to verify that any force is being generated:
  1. If the ball goes through the floor, your floor might be so thin that the solver doesn't even notice that it is there. Make sure it isn't too thin, and make sure your step size and tolerances are tight enough so that it will notice that the floor is there.
  2. Make sure your floor is oriented properly - you can visualize the surfaces that the contact force library is checking on the "Visual" tab.
Next: Make sure your stiffness is high enough
This is the process you were already following. Once your stiffness will prevent the ball from going through the floor, adjust it so that the penetration at rest is reasonable. You will need to increase the damping as you increase the stiffness.
Good luck!
--Steve

Categorie

Scopri di più su Applications in Help Center e File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by