I found this bug when attaching a contact sensor to a model, with DART physics engine and Gazebo 9.
When I display the gazebo topic associated with this sensor, I can see that the normals of the contacts are not constant, even if the model is lying on the ground and is at rest (only gravity force is applied on it). More precisely, the directions of the normals oscillate between approximately (0, 0, 1), and (-0, -0, -1). The sign of the associated force also vary accordingly.
The bug is very easy to reproduce, you just need to attach a contact sensor to a model, and display the associated gazebo topic.
This is a blocker for my application, so any help is appreciated! Do someone know in which class/function I should look to find this bug ? I think it may be in RetrieveDARTCollisions, because a lot of contacts related things are made here, even if I don’t see anything about the contact normal…