First problem im having with this is the twisting of the upper arm due to lack of stiffness, which is mandatory for this case. Another reason why i went with the high gravity, since that way the stiffness could be increased and you just had a dropping arm without the twist. Would be great if there could be a stiffness parameter for each axis…
Next problem is the arm colliding with the body, there is no impact effect. I know there is the bounce parameter and its also on default, which should give realistic results as it is. Am cautious increasing it after my last tests a while ago, since it made couple parts jump invinitely.
Lastly the arm behaviour when pulled by the pin constraint. Feels like a bit too less inertia of mass for my taste.