I have already received the notification from UPS that the challenge kit will arrive next Tuesday 19; in the meantime, the exhibition installation goes ahead. Lorenzo's operas will create a path for visitors. As there are many different points of view you can read Art-a-Tronic, as well there are different paths you can follow visiting the exhibition.
Moving the Mannequin
An almost complex part is adding the motion to the mannequin. The problem is that it has been designed and build more than half a century ago so integrating some sort of movement in it sounds very difficult. Unfortunately, the head is fixed; probably it is possible to cut the neck in the middle adding some rotation but I think that this will penalize too much the aesthetics so the head will remain fixed. There are five points that can be moved corresponding to the articulated parts of the mannequin: wrists, shoulders, and torso.
I have also considered that all the motion interventions will include some kind of alteration in the form of the joints but this can be easily masked properly dressing the parts.
There is also another important consideration; to control the motion I expect to interface a dedicated microcontroller able to manage the low-level motor motion part autonomously and in part receiving orders from the brain, the Raspberry PI 3B+
Thinking on How to Move the Torso
Torso - or, better, the upper part of the body - is fixed through an axle screwed on the upper plane of the legs (that can't move). The first ides was using a couple of motors pushing vertically from the torso with threaded bars but this implied a lot of mechanical problems, including fixing the motors on the upper part and the thread bars attach to the bottom parts.
Excluding the possibility to have the torso oscillating I decided for a single-motor solution acting as a linear transducer as shown in the stepper parts positioned approximately in their asset shown in the image below.
Using this Stepper motor just makes the body taller some cm so it is acceptable without losing the aesthetical body proportions.
The two images below show the legs upper surface by the plant. I will start from this point to design the parts that must fit inside this space.
The Most Affordable Solution
I have reviewed in detail the possible solutions to move the torso. The initial idea - very similar to those suggested by beacon_dave (Dave Ingels_ - sounds attracting but reviewing in depth how the two parts mannequin is joined arise a lot of difficulties, with the risk to be not feasible in a good way. The images below show how the central joint is an essential part of the entire torso support and can't be avoided. the lock nut is part of the system keeping together the two legs, as a matter of fact, the bottom half of the body.
Changing this part means to replace is rebuilding one in a different way and in my opinion it is not the worth as the same result can be reached in an easiest way, apparently more complex but that requires definitely less extra 3D printed parts.
As shown in the above image, the shaft is not just a bar but includes a turnable spring to keep the torso in the desired orientation. This sounds good to fine-tune the upper part when there is the motor with the linear transducer. Following this proof of concept I have drafted a quoted sketch to fix the ideas before proceeding to model the parts that should be 3D printed.
I should make only two parts for the bottom: the stepper support that should be fixed to the plane and the back side support. To make it working without attrite, I will use a free fall bearing, part of the same 3D printing. Note that in the sketch I have designed only the bottom guide for the back of the torso but in reality, there is a counterpart that will be fixed to the bottom of the torso; both together will be thick like the motor. The threaded bar is oriented horizontally to the longitudinal (the longest side) of the torso in correspondence to the mannequin belly to be completely hidden.
So, don't lose the next episode.