Unexpected behavior when using passive joints in closed-loop kinematic chains

[huemerj]

Probably related to #219, I experienced problems using passive joints when updating from 0.4.3 to 0.4.4 on humble.
More specifically, I simulate an actively controlled hydraulic cylinder acting on a passive joint in a closed-loop kinematic chain, which I need to get the state from.
As in #219, the passive joint is now fixed, even if it should be moving.

I narrowed down the problem to this part of the code, introduced in #177:

gazebo_ros2_control/gazebo_ros2_control/src/gazebo_system.cpp

Lines 597 to 600 in 0dc19ab

	} else {
	// Fallback case is a velocity command of zero
	this->dataPtr->sim_joints_[j]->SetVelocity(0, 0.0);
	}

[destogl]

Thanks for reporting the issue. The issue is that we don't filter the passive joints. I propose to add a new map or vector with flags is joint is passive or not, and if it is passive, then we don't set the velocity here. A good place to fill this vector is after all interfaces are parsed on the line 296. A passive joints can be detected that there a no command interfaces, but only state interfaces.

[christophfroehlich]

fixed with #237