I have this unanchored model which has a main unanchored part with all the parts in the model connected to the main part with weldconstraints and I have 1 motor6d in the main part that has its part0 set as itself and part1 set as an anchored part in another model. The model works fully as expected like this its just that I cant tween the main part even though its all welded.
You should instead anchor the main part and unanchor the anchored part.
this simply isnt a possibility because im scripting this for planes which have to have the animated parts unanchored to function. And also this makes me not able to use the motor6d just for simple rotation stuff.