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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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  • Hi Enrico,

     

    This is a really exciting project : ) Looking forward to seeing it progress!

    Regarding the torso, you've got a lot more experience in motion and motors I think, so this idea I'm about to suggest may have issues to rule it out, but just in case it gives any further ideas: I was wondering if a Lasy Susan type device could be fitted (I think this could be identical to what you're considering with the metal ball bearings if I understand correctly), so that the torso can turn freely, and then use a motor and gearbox, to turn thin steel strip (or it could be plastic strip) - just like a reel of measuring tape basically.. The strip is strong enough so that it would push the lazy susan, but flexible enough so that it can go in a curve. One end of the strip is secured to the motor, and the other end of the strip is secured to the top half of the lazy susan.

    The benefit of the strip could be that there is no need for accuracy like with gears. I've never tried this though, so in practice it might not work. I think it may also need some 3D-printed curve around the lazy susan, so that the tape is forced to follow that curved path, when the motor is turning counter-clockwise.

    image

  • in reply to shabaz

    Hello Shabaz! Thank you and let me comment on your suggestions.

     

    About the ball bearing on the support you are correct, it's what I aim to do. It is efficient, stable and gives very few attrite as well as smooth motion, and has the advantage that you are not obliged to design the mechanics depending on the bearings you can use.

    image

    Instead about the Lazy Susan. Frankly, I had no idea that it was the right name of this kind of mechanical solutions, but the name is not new so probably I already found it somewhere else. The idea is affordable but I have doubts about its applicability in this specific context. If I have understood correctly this technique is assimilable to a sort of Half pulley, maybe with metal or something robust. The question is... How is managed the back path? Rotating the torso (about 1Kg plus electronic and some other stuff, despite I will keep it as lightweight as possible) is bi-directional with a centered position, so the mannequin can rotate right and left. Please, can you explain more in detail? As far as I know, at the moment the only application in a context like this is with a mechanism including a return spring when the motor relaxes the band, but this is possible in cases when despite the push/pull direction only one of these directions require extra force by the motor so the traction is actuated by the band and return is something like spontaneous where the motor is just controlling the motion. Or there is something I don't know of this mechanism at the moment.

    ATTENTION! HERE I HAD THE ILLUMINATION!!! FINALLY, I UNDERSTOOD YOUR SUGGESTION

    Investigated on a bit more and found this: Triangle Manufacturing - Lazy Susan Bearing Applications  So, what I am doing with the bearings (bought 1000 3.5 mm bearing balls) is a Lazy Susan mechanism? I used it in a lot of cases, loved it and never known its right name image image image image

     

    Well. Please, let me rewind a moment and see what can be right from both our ideas (including the non-viable suggestion of that opened the door to find alternatives).

     

    1. The large base support should be added as it is non-regular surface and I need the torso moves smoothly on the Lazy Susan (yeeee) bearing but also creates a base similar. Anyway it can be reduced and probably made more regular
    2. The use of gears should be excluded, not really for the design complexity but because the system is and should remain a bit fuzzy. Using gears for life-like movements generates sorts of Frankenstein effect or a lot of software to manage the right acceleration and deceleration curves is needed.
    3. The threaded bar solution can be excluded too as maybe easier than the gearing mechanism but implies two vertical rotating nodes, two bearings and the distance body-torso may increase too much. I have considered this kind of motion and two nodes are indispensable. Look at the sketch below.

    image

    Assuming that A is in the midpoint of the threaded bar and B is the motor when moving the torso rotating around the center of rotation O (the already existing shaft) Moving the torso from point A to A' the node should rotate by the angle beta and the motor should rotate by the angle alpha. (If I am not wrong, alpha and beta are complementary?) This means that both the motor and the torso node should be mechanical complex, with bearing, rotation etc.

     

    Based on these considerations, I will redesign the rotation mechanism but using the motor connected to the Lazy Susan base with a fixed tooth belt. The large pulley should not be complete but only will support the small angles rotation in both directions. With the advantage that - ad Dave correctly suggested - the distance base-torso decrease as the motor can fit inside the already present hole of the top leg base.

     

    Please, let me know if this sounds reliable. Enrico

  • in reply to balearicdynamics

    Hi Enrico!

     

    Yes I think tooth belt and pulley idea should work too.

    Regarding omniwheel/mecanum wheel, it's a shame they are so expensive : ( I saw a really nice robot platform at an exhibition, they used such wheels. It was a very powerful robot, the guy was sitting on it and could manoeuvre incredibly well.

    I looked at the time for low-cost versions, some were really bad, but these looked nice I thought.. still not cheap though:

    https://www.aliexpress.com/item/Four-Blue-Mecanum-Wheel-60mm-Wheat-Wheel-Omni-Wheel-Coupling-Mecanum-Wheel-with-the-Pric…

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