ratio of arms mechanism is 12:20 x 8:24 = 1/5.
Universal joints allow arms bending
inwards and outwards.
So placed, the motor resembles J5
arms position is a bit affected when torso is lifted:
this is due to axle sharing between multiple mechanisms.
This is a minor defect of the complex
parallel kinematic structure
that mantains shoulders correctly
aligned to the ground, both when J5's torso is raised or lowered.