I'm using Gazebo 11 + DART 6 + Bullet collision checking and I run the simulation as fast as possible (i.e. I set <real_time_update_rate>0</real_time_update_rate>) . I noticed something weird: my simulation starts and the real-time factor is initially around 3.5 (for approx 10 seconds) and then over the course of approx 1 min wall time it drops to a much lower real-time factor of around 2.3 and stays there. I am not doing anything inside of the simulation that could slow it down. What could be the cause of this?
I checked with htop and none of my nodes are using excessive CPU power. I noticed that this doesn't happen with the FCL collision checker: the real-time factor stays constant at approx 1.2 (as expected). So I don't think this is a problem with my code.