I've been teaching myself freeCAD and using Autodesk inventor fusion too. My first main use as a learning tool is designing a new airframe for the cheap little quadcopter that I'm always breaking. I'm designing it so that I can just swap over all of the electronics from the broken quad and also to add a tiny camera for fun aerial shots. My dreams and long term goals are much bigger than my current skill set...I'm still a newb.