For my projects, I try to learn as far as possible from marionettes. After a while on Internet, I discovered W.A. Dwiggins (1880-1956) from USA (Ohio). This man is known for writting fonts and… Marionette in motion.
Here is a quote (1939):
“[The marionettes] are moved by two opposed forces, by gravity, pulling down; and by you at the end of a string, pulling up. But in working out marionette mechanics it is helpful to forget the fact of the two forces and to think of the downward pull of the gravity as the only force operating - to consider that your function with the string is simply to control the motions that result from the pull of gravity. Gravity does the work - say - you control the work.”
It is more inspiring than I expected. You will find in this small book advice to build humanoïd moving shapes taking into account mechanical stops and balance rules (more than geometry). There is a kind of magic in it 
.
Look at this one named “Lilith”
This system has inspired lots of companies and for instance the Mainstring theater company (who made me discover W.A. Dwiggins).