This is a followup to the question here:
http://answers.gazebosim.org/question/17153/manipulator-joint-constraints/
I can't seem to figure out how the fourth link causes problems depicted here, when spawning the model. If I try to fix the base of the model to the world, everything seems fine until I start moving the joint, then it just breaks again. can this be caused, again by inertia? Or is there some typo or something that I'm not seeing...
Here is the code:
https://pastebin.com/asvmHPG9
Here is the result when spawning model without fixing the base, with fixed base after moving a joint it looks the same.