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  • Author Author: balearicdynamics
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Art-a-Tronic Episode 2

balearicdynamics

Introduction

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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

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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.

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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.

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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.

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The Most Affordable Solution

Update

I have reviewed in detail the possible solutions to move the torso. The initial idea - very similar to those suggested by (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.

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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.

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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.

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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.

 

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  • in reply to beacon_dave

    I find this idea genial, as simple. Sure it is something not so easy to build, maybe the case to find some of it for a sample project.

    BTWm in my creative dreams there are also the omniwheels, but seeing how much these cost a piece the only solution is making the 3D printed at home.

     

    Enrico

  • in reply to mcb1

    Hi Mark,

     

    thank you for your contribution. I am happy that this project is creating attention stimulating suggestions and criticism.

    Well, I have checked again the details but this solution is not viable. This is a mannequin of the mid of the '60s: heavy, well done and most of the parts are really well refined by hand. Advantages and disadvantages...

     

    The legs are two and the bottom part of the body is divided in two parts, joined inside (the hole is just to close the joint nut. The same joint is the support for the shaft bottom M4 screw with the blockage nut. The problem of the spherical support is meaningless as the top regulation of the shaft act to the inside spring and metal cylinder to lock the shaft in the desired position. It is very robust when locked (if should support in the original design, both the torso and the dressing). This is fundamental as the body planes separating the two halves are not perfectly plane, just well refined. The entire shaft length (25 mm diameter) will fit inside the body to keep in position at the right azimuth but it is fundamental that the torso is based on something almost large.

    You mention geared motors (excluded as I should make specific movements so the choice is for a stepper). But probably not evident in the images, this stuff is a 1.80 tall real size person build without material economy in mind. The torso, empty as it is now, is about 5.5 Kg that will probably reach 6.5 with the stuff I will add. So the Nema 17 stepper motor and the reduction of the pulley is the minimum essential to be able to move it without too much effort.

    Mixing the various ideas I have discussed until now the solution I am trying to design for now is Lazy Susan bearing on the peripheral, the motor inside the base of the legs (not exactly in-axis with the shaft), and a reduction pulley of 150 mm diameter. As the rotation angle should be about +30 / -30 Deg, I will try to use a 2 mm tooth belt to join the big pulley (fixed to the dorso bottom) together with the small (20 teeth) pulley on the motor shaft.

     

    Enrico

  • in reply to shabaz

    a little off-topic perhaps but speaking of steel tape, have you ever come across the Spiralift lift motor assembly ?

    https://www.youtube.com/watch?v=re552s7bnfU

    Two steel bands that interlock to build a sturdy rising column.

     

    - something for a future project perhaps ?

  • Enrico

    Depending on the hole in the upper body, you should be able to add a normal bearing that resides on the top of the threaded bolt

    image

    The inner race will sit on this, while the outer supports the body.

    It may require a small spacer or 3D printed part to go between the bearing and other parts.

     

     

    I'd also replace the spherical bottom bolt with a fixed version so that the torso and legs are in the same plane.

    image

     

    I'd then use a wooden ring attached to the upper body, and a rubber wheel pressing against the inside (or outside) of the ring to make it rotate.

    You should be able to mount the motor through the leg.

    I you make the motor and wheel sprung loaded, it would allow for any off centre issues and allow the tension to be adjusted.

     

    There are plenty of geared motors, or a geared stepper motor should give enough torque and be much smaller than the one above.

     

     

    Cheers

    Mark