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Thread: Robotic Marionette

  1. #11
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    Nov 2008
    Gainesville, Florida
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    Talking Re: Robotic Marionette

    Back from a delicious plate of pasta with Reggiano Parmesano

    Sculpting the model

    Although I intended to use traditional wood for most of the body, I wanted to try to make some parts with Apoxie Sculpt and Apoxie Clay, some of my favorite sculpting materials for small models, prototypes or part replacements. The only drawback in this case was the weight, but I though that maybe not in the case of the hip which being the center of gravity could have some extra weight.

    I left the ball of clay harden a little too much and so after whittling away for a while I finally gave up because it went past the "leathery" state which is so pleasant to work with.

    Now it was up to power tools to pick up. I had to wait a couple of days for it to harden enough and not gum-up the blades or the sandpaper. I like to avoid power tools as much as possible because I really love sculpting, whittling and shaping with my hands and some simple tools.

    I really like the line of Apoxie products. I recommend them to my students and I use them frequently. They are easy to work with , extremely durable and have good mechanical resistance. Not to mention shelf-life!.

    I found a couple of containers that had a bit left and had been "lost" for over three years. They were on the humid and very hot environment of the Florida swamp. That is just the opposite of what they recommend; 'refrigerated and dry to extend shelf life'

    Well, other than being a little harder at first, after kneading it for a few minutes they came back to life and behaved as expected.

    Now, if they only gave me a discount for the plug :-)

    After cutting most of the extra epoxy with the trusty old Dremel (the new ones are plastic crap!) I proceeded to sand and sand away from 80 to 1200 grit until the shape fit my template.

    The hip was now so smooth and polished! It felt great to the touch. I thought I could use it instead of wood since it seemed to have the proper weight. Once assembled though, I knew the total weight was too much for the medium servos that I planned to use.

    After finishing this stage of the hip I drilled and installed attachment points for the legs and the waist, which is the next piece.

    The waist unit is finished except for the holes and restrains that will attach it to the hip. This piece was so much easier because I did not let the Apoxie harden and I was able to model it with my hands almost to the exact shape, so it only took a bit of sanding and polishing. On to the legs!

    There are so many ways to make legs and knee joints!

    This was my first pass, I didn't think would be the last until it was finished, polished, assembled (the hard part) and tested. I was using white pine, it had quite a bit of resin, which made it hard to carve and sand.

    At least it is not as hard or life-critical as the prosthetic knees that biomedical engineers have to fashion for their patients!

    I used some of those knee models to make a sculpture and as we found out, it was the hardest and most exotic material (titanium-vanadium) we could ever work with! It was worth it, and also gave me an insight as to how strong and durable future cyborgs will be.

    Attachment 789
    My friend Brad (left) and myself after sweating it out to create the sculpture from conception to delivery in a record three days! Now, why couldn't I work as fast for this project?

    Brad and myself created this sculpture as a recognition gift for Dr. J. Crayton Pruitt, who had just donated 10 million dollars (das ist recht!) to the Biomedical Engineering Department of the University of Florida.

    Attachment 790
    Dr. J. Crayton Pruitt, as pleased with his gift as UF was with his!

    So we thought appropriate to use some of those vanadium knee parts to serve as the pivot point of the sculpture, the rest of which consisted of beautiful alabaster that slowed light as it absorbed it, as only alabaster can. The wood base was made with an exotic Brazilian hardwood and the plaque was made from aluminum scavenged from the Aerospace Engineering bin and obsessively polished.

    Attachment 788
    These are some examples. Imagine the possibilities!
    Assuming you have the tools to make a dent or solder the critters.

    He must have liked the sculpture because ever since then we receive (Brad and I) a yearly crate of Florida wine from his own vineyard. Thank you Dr. Pruitt! :-)

    So far the hardest part was to drill the holes through the Apoxie and line them up correctly. That sent me back to examine very carefully old unfinished puppets from the Dwiggins archive. I learned a valuable lesson: the holes must be drilled BEFORE you shape the form (DUH!), otherwise lining up and holding the shape correctly in different axis becomes almost impossible. That meant that the use of Apoxie for main body parts was not the best solution, since it would be a real waste to create first a block and then cut and sand it down.

    That said I am very pleased with the look and feel of those two parts, which strike me as very "Japanese" (or Brancusian) in some way. The only un-japanese thing about them is the misalignment and lack of precision of some of the through-holes on the back due to the reasons explained above. No excuses, (Julie Taymor would be very upset).

    The fondest memory I have after enjoying many days watching the construction of a Japanese Tea House by a master carpenter was how every single piece of assemblage, including those that would never be seen by anybody, were as perfect as the main "public" pieces. The sculptural quality and the loving care and treatment of the most humble of materials left a permanent impression on me. I have a long way to go.

    Next in line was to attach the legs which were already temporarily assembled and test the lower body for problems. After that I shaped the legs to give the Creator that sophisticated look that I am sure it craved

    To be continued...
    Last edited by sunithaya; 12-01-2008 at 11:49 PM. Reason: trimming
    You never change things by fighting the existing reality. To change
    something, build a new model that makes the existing model obsolete.

    --R. Buckminster Fuller

  2. #12
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    Apr 2008
    Nelson, New Zealand
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    Re: Robotic Marionette

    This is so cool, I love reading every bit of it, Keep it coming sunithaya.
    People yearn after this robotic dream, but you can't strip your life of all meaning, emotion and feeling and expect to function.

  3. #13
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    Gainesville, Florida
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    Re: Robotic Marionette

    The Power of Tools

    Attachment 803

    I started the Creator's torso by finding an appropriate block of wood. I had intended to use pine since it is soft and easy to carve, but I had none of the right dimensions. My only option was cypress, which I like a lot for its color and its pattern, but is considerably harder and demands a lot of attention to the direction in which you whittle it. That means you have to be really careful to follow the pattern of the rings and watch when it changes direction if you don't want your blade to get caught and possibly damage the wood, specially when you approach the final surface.

    A very important thing when you carve, specially at the beginning when you apply a lot more force to approximate the shape you need, is to be able to hold the piece securely. There might be other techniques and of course you can improvise, but if you have access to the magnificent and versatile Jorgensen clamps, use them!

    If it had been pine I could have done it with a set of X-Acto knives without much problem. But for any hardwood you need proper carving tools, I have found that Warren Tools are an excellent choice. I have had my "traveling set" for over twenty years or more when I bought them to carve my first "professional" puppet out of basswood. I've kept that set like a treasure through many life changes and moving from continent to continent. I have lost many things but not this little box. True, there are finer and more expensive carving tools out there but here you have a balance between price, quality and workmanship.

    I talk about tools often because I think that tools and the art they enable are inextricable linked, "...where form and function are most closely related as a way to understand and influence our most basic aesthetic and ethical decisions". I also think that great tool design can only be achieved by someone who has mastered his or her craft and realizes the importance of the interface between your mind and the object you intend to create.

    Whittling is not done much anymore since the advent of power tools, the same way that cooking (and eating!) has pathetically been replaced by TV dinners specially in American households and definitely in student's dorms. TV watching has taken the place of meditation and your organizer has replaced your capacity to memorize. All I can say is that the magic of discovering the shape that lies inside that block of wood as you approach its delicate surface is one of the greatest rewards.

    Attachment 798Attachment 797

    The Beauty of the Fall

    The beauty of the Püterschein system is, as you can see in this picture, that the puppet assumes very natural positions with no human intervention. I just cut the string that held it up and it fell on its knees just like that! A true predecessor of inverse kinematics!.

    Attachment 810Attachment 809
    It seems like it is praying for arms, looking intently at the cut rods that will give it the expressiveness it needs.

    I cut an old broom stick to use for the arms, thinking that it was pine and it would save me some time if it already had a round shape. Ha! I don't know what kind of wood it was, but it was hard as oak and I went through a whole set of carbon steel blades just cutting it down to shape. It took me three full days to get them ready for testing! So much for saving time...

    Attachment 808

    You can see the Creator now just standing naturally, again with only spine support. I did not pose it, other than bringing it down to contact a surface. Couldn't wait to have the entire body functional. In case you are wondering the "feet" would be two slim inverted metal cones. As for hands it will have none in this iteration, since it will be all dressed up and have very long sleeves like the human performer you can see here
    This is a detail of the hip and waist rigging that holds and constrains those parts as the marionette flexes and moves.

    Attachment 804Attachment 805

    After three days, a few cuts and sore muscles overall, the arms were close to ready. I tested them and they moved gracefully and have the needed range. Under the torso you can see the channel I gouged out to make room for a couple of screw eyes to pass the string that connects it to the waist and hip.

    Next task: the HEAD! this will be interesting since it will have a wooden core or "skull" and it will wear a "self animated" mask, a fancy way of saying it will have some springs to react to any movement of the head. If I have time, which I doubt, I would like to put a micro-servo on the latex mask so that it can have a range of expressions in addition to the eyes. Lorena, who designed the original creature does not like the idea. Perhaps she is right. The simplicity of the spring solution, which we have demonstrated on performance gives such a varied range of expression to the Creator's face that adding more might be less. So there!
    Last edited by sunithaya; 12-02-2008 at 09:20 PM. Reason: trimmimg
    You never change things by fighting the existing reality. To change
    something, build a new model that makes the existing model obsolete.

    --R. Buckminster Fuller

  4. #14
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    Gainesville, Florida
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    Re: Robotic Marionette

    Hip Gnosis

    Do and learn. The hip and waist proved to be not only very heavy but also out of proportion. Looking back, this happened because I scaled the entire original schematic to simply make it taller without really thinking through the proportion of the individual body parts.

    So, here I go again. I redesigned both hip and waist and decided to use pine wood instead, cutting the overall weight considerably by almost 300 g. My servos were happy!

    Since I was going to start from a wood block this time, I was able to drill the holes in a more controlled fashion, sort of, because some of them traversed the block at extreme angles. But overall this fact alone made the parts fit better. Molding the parts with Apoxy was fun and quite easy and fast, but not the right solution in this case.

    Here you can see the difference in size and weight, of the old and new hip-waist combo. Of course the scale change rippled through the entire puppet since I had to also modify the torso and the legs. I knew I had to do the same with the arms, which I put on hold for a while because the wood was so amazingly hard. But it happened.

    String Instrument

    Attachment 814

    Here is the Creator waiting to have his nervous system installed. The secret to a balanced marionette lies mostly in the stringing that controls it both internally and externally.

    The strings that hold the different parts of the body from the inside act as ligaments as well as nerves, that stabilize and enable the parts to move in relationship to each other. By transferring forces and movement information through the spinal string, which is the case with our body, it keeps us balanced and acts as a conduit through which our brain controls our movement.

    In the case of a traditional marionette, that brain or intelligence comes from the learned hand of the player of the strings, the puppeteer.

    In this case it will be the computer or rather the microprocessor, together with the sensorial system that feeds it information about its environment, that will make the equivalent of conscious decisions as to what to do and when.

    The other part, the involuntary movements, the character, arise from the structure that has evolved from interacting with the laws and forces that constitute the semiotic "liquid" in which the creature evolves.

    This evolution has produced the structural support (skeleton) and the relationship between the systems that allow both us and a marionette designed under those principles to act and respond accordingly, with or without consciousness or awareness of that which ultimately controls us.

    Attachment 816
    This sequence was produced simply by lowering
    the spinal control until it no longer supports the body.
    Last edited by sunithaya; 12-02-2008 at 11:16 PM. Reason: addition
    You never change things by fighting the existing reality. To change
    something, build a new model that makes the existing model obsolete.

    --R. Buckminster Fuller

  5. #15
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    Re: Robotic Marionette

    Gimme Shelter

    Attachment 846

    Time to create the scaffolding for the Creator's shelter. It will hopefully be as functional and form(ally) beautiful as it can be. In trying to find the right tools and materials I bought some Vex kits when Radio Shack decided to chuck them. So in a way I got a good deal. From a tinkerer's perspective though I wish I had my (very) old Meccano, which from an engineering perspective was a lot more versatile I believe.

    The problem with the Vex "system" is that it is not really versatile. It seems to have been designed, not as an optimal modular construction set, but rather limited to some preconceived ideas as to what you should do with it rather than let you decide, others might disagree.

    I find it very limiting for free form design. Take this example. To construct the very simple structure I needed required me to use ALL 5 kits! and it was not enough!.
    When you think of which is the most useful and common structural element in construction, I am sure that the majority of "builders" or engineers would agree that it is the humble angle, strong, simple and functional. Well, guess what, the entire Vex kit comes with a whooping 3 angles! yes, that is 1,2,3! But what were they thinking?

    This forced me to construct the main columns with rails (of which there are quite a few) which prevented me to attach the rest of the support elements in a simple way.

    The kit does come with lots of elements that might have some use in some predetermined project but it is the least useful grouping of parts in any construction kit that I have found. There must be a reason behind this, and it is probably very sound, like ka-ching! Almost any project will require you to buy extra hardware, at a very steep price, and you can bet (and would win) that the "dedicated" hardware kits bring a completely unbalanced set of elements as well, so that you do keep on buying. Bear in mind that I am not building anything exotic as you can see from the pics.

    The structure is 80 cm. tall and 33cm wide, making it a harmonic rectangle area. Of course it is not exact, since it never occurred to the designers that anybody might need , want or know about such things as harmonic proportions.

    OK, I was a little pissed off, since the kits did not fulfill my expectations.

    [CENTER]Stage Hands

    Attachment 851
    Assembling the motion section and adjusting the elements so they fit.

    I love that time when you have to finally begin working on the stage for a play. It means the performance is imminent (unless the producer pulls out!). It is also time to listen carefully to the director, designer, performers, lighting and sound people and stage hands and riggers to make sure all points of view are represented and taken into consideration. (if only it was like that in real life...)

    Since the hole pattern in the VeX system is not really well designed (unless someone proves me wrong) I had to notch and cut lots of pieces so that they overlapped correctly in the configuration I needed. As I said before, I think the engineer/s who designed the system probably did it with a preset number of projects in their mind.

    I would go back to the drawing board. It seems strange to me that in this age of CAD and relational tools, they could not test at least a few thousand combinations and optimize the design for that. So anyway, the metal is soft enough that it doesn't take that long to adjust.

    Attachment 852
    The Vex control modules, servos and power supply.

    Except for Lorena, my wife, who is the human performer, choreographer and costume designer for the project and who makes sure her needs and demands are met:-), the rest of the crew is me with occasional help from my friends, like Philip who is working on a Flash Develop interface to control the microprocessors and sensors. I had my doubts about the speed of the image processing functions in the new Open Source Flash, but it was worth a try.

    At first I was using VeX to build the stage support and to prototype the motion and control system. I was trying to decide which microprocessor to use, perhaps Propeller by Parallax which is a multi processor where each one of the 8 cogs that can operate simultaneously giving you the ability to respond in real time to performer actions, which is what I needed to do.

    Easier said than done, since programming is not my strenght, but my friend Philip loves coding and we have done great work together. I needed to complete the prototype so that I we could start programming and optimizing. Everything simpler, easier, faster. Like Ars Electronica's 2006 theme said, SIMPLICITY - the art of complexity.

    Attachment 853
    The Creator's new feet

    I was also getting so much more familiar with the marionette I had created, since while you are whittling away at blocks of wood and dealing with joints, balance and many other issues, it is difficult to meet the creature on its own terms. Although it was not awake yet I could already see a bit of its character and personality. This is an experience which every puppeteer, or for that matter any artist goes through as it transitions from production to contemplation or analysis and finally to understanding or appreciation.

    This process is not so familiar to the engineering folks, since for them, in the majority of cases, everything must be defined or though in toto in advance and there is usually little room for improvisation. I don't mean this as a criticism, simply as a pattern that I have observed although as in everything there are exceptional exceptions, and I think many of those exceptions hang out in this forum!

    Do Not Read This if You Value Your Time!

    On the banal but also symptomatic stage of the general deterioration of ethics and quality in our world and in particular where I live, I received a large package on the mail that I had no clue as to the contents, since I did not remember ordering anything as large...

    Since I don't have a lathe or access to one at the moment I thought it would be easy to find the small pulleys that I urgently need for my project. As it happens, one of the most difficult things to find have been the pulleys or sheaves needed to raise and lower the marionette's articulations.

    Why this is I don't understand. No robotic store or company, specially at the "hobby" or craft level carries such a useful and logic device. Can someone explain?

    After much searching I finally found a place that purportedly had what I needed. Based on their description I bought 6 little sheaves to test. Here is what I got!

    A ridiculously large box with 6 little pieces of very crappy malformed plastic. Supposedly this place, whose motto is "Leaders in Education" wants to lead students, in step with the current government mandate to the lemmings paradise.

    I imagine, they consider children or students simple ignorant people who do not deserve to touch anything decently made that might, just might, teach them something. That way they learn to accept as a fact of life the terribly poor quality of life that education (with few exceptions) in our country provides to the millions, ground and trained through the system to accept mediocrity as the norm.
    Attachment 855
    Take a close look!

    We ship the crafts I or my wife make all over the US and the rest of the world. One pound, Priority Mail costs $US 4.80 ...the shipping of these few ounces of bad plastic which cost US$ 1.50/each, cost US$ 7.oo for a total of US$ 16.00 I guess the huge box accounts for the "handling" fees.

    I understand this post is a waste of everyone's time. But it is also part of the process which includes frustration from which you must recover. So back to a more positive track I decided to build my own pulleys with wood. I shaped them with a sander given the lack of a lathe, but that was OK.

    What was I thinking!!!

    Just to finish the pulley rant, I created a template to drill the round wood pieces that I bought (99c/bag) at the local craft store. They seemed perfectly round in the bag...

    Much to my surprise (am I new? or what!) they were far from round, I found out when I tried to fit them in my template. To make it short, I sanded them enough to fit, drilled and glued them together. As I was venting my frustration for not finding proper pulleys, my wife who works next to me in the studio, asked why I did not use the spools that she uses for her beading or the ones that I use for stringing (fish line) the marionette.

    I must have been very tired, sleeping 4 hours max for months. Why didn't I think of the spools which were in front of me? So, there, I had a steady supply of the perfect size/weight spools.
    I only needed to create bushings to adapt to the servos, real servos that is, not the modified ones by Vex which of course have a "proprietary" square shaft that only fits their kit stuff, I still cannot get over their lack of foresight and integration with the rest of the world. So much for Open Anything! Dean Kamen, you know much better than that!

    I created the bushings with an aluminum rod that happened to have the right diameter.
    I drilled the shaft hole to attach the Hi-Tech servos I intended to use, notched them to hold the adhesive better and epoxied them to the spools.

    Command and Control

    The recent integration of the Make controller with the open source Flash Develop, its scripting language and image processing capabilities, solved many of the problems I was dealing with, from the choice of microcontroller to the controlling software.

    The program currently reads the position of the performer on stage and even the distance from head to ground, all with only one cheap webcam as an input device. There is so much information that can be acquired through image analysis that effectively eliminates the need for a variety of sensors that I had planned to use.

    The only limitation is the amount of servo ports in the controller. I had to use at least two, to handle all the servos I needed.

    The servo that supports the weight of the marionette most of the time needs much higher torque than the ones I have. I ordered a Hi-Tech Mega Giant Scale Servo ASAP to start testing the software that Philip and I were designing. I was very excited and happy with the progress so far. At first I had my doubts that the solution he proposed would work, but now I see it can, and in a very simple and elegant way.

    The two sizes of spools we currently use (5 and 8 cm diameter) happened to have the perfect circumference to provide most of the travel that I need without using continuous rotation motors instead of standard servos. This simplifies programing. We found out by testing a variety of "identical" modified servo motors that the speed of rotation, given equal parameters, is quite different, which implies writing routines to address each one of them to synchronize, a royal pain!
    Attachment 835
    The fish-line spools with their bushings in place

    The only continuous rotation motors I needed were for the arms since they travel a much greater distance.

    Snap to Grid
    Attachment 845
    Serious construction began. This had to be, want it or not, the last stretch of the building process for the Creator stage.

    But before I begin this section I want to share a tip that I take for granted, but friends that see it are always amused by it. You know that when you work on a project involving dozens or hundreds of small pieces, screws, washers and what not, things like to go amiss. Lost socks pale in comparison, specially when you lose a servo screw that you won't find in any hardware store (unless you live in the Bay Area, how I miss that!). And ordering a screw or two online just does not cut it.
    So, I use a big magnet block (which I don't remember where I got) and simply and literally throw all those little pieces at it, even from quite a distance and it just snaps them as they try to go by. Sometimes I am working on an odd position, (upside down ?) and as I disassemble something, which happens more and more often as I try to refine my design, I start collecting all these little pieces in my hand and mouth that are eager to disappear in the cracks of the floor or my stomach. Well, just toss'em up like a chef flipping pancakes towards the magnetic field and , snap! they are not going anywhere.

    Now, mind you that this is not a very powerful magnet, like those neodymium or ceramic magnets that you find in hard drives otherwise getting a washer back would probably be impossible, but it is strong enough to hold quite a bit of stuff. Sometimes you cannot even see the magnet anymore, just a weird nut screwy sculpture.

    Divided and Conquer

    That seems to be the design philosophy of the VEX guys. I promise (well, a weak promise) that I won't waste more time bitching about their "close source" design decisions. But someone has to say something. Of course I used their stuff to prototype my project since I had bought 5 or 6 kits with the hope of actually using them for the final project. Now, to be fair, their nuts and screws are first rate and I have no complaints, as well as their cute chain transports if you use their square shafts of course, but the rest...

    It was obvious pretty soon that the electronic/hardware side would not work due to their very flimsy nature and weak linkage (or lack of it). Take their servo for example. Not only is it far from standard, so that you can hardly mix with any other brand, but it lacks fundamental elements like a horn or attachment plate of some sort so that you can drive something more than their absurd square shafts.

    And guess what, you cannot even screw anything to it, you can only use their "clutch" (the small cylinder with a short square stub) to attach another square shaft to drive any square holed device! BTW the clutch and therefore anything attached to it, will simply fall off if you turn it upside down. Am I missing a screw here?

    You cannot see it in this next picture, but those arms or extensions that I need to drive the limbs of the marionette with have as much strength and stability as an apple stuck on the tip of a drinking straw, can you picture that?. The main reason being that as I explained, the servos connect to anything else through the wimpy clutch mechanism that cannot stand any side pressure, only direct transmission to a wheel at the most.

    To be fair, after a great deal of literally hacking away with a saw, drilling and cutting and bending, I was able to put together a somewhat functional scaffolding for the stage. If I had the money I would simply make everything from scratch out of aluminum and some steel pieces. And, yes, chuck those servos away. I opened one to convert it, I was so shocked by the poor craftsmanship inside, probably built on a Chinese sweatshop (badly soldered by hand), that I just closed it and proceeded to order a set of excellent Hi-Tech servos.

    Give me a big enough lever...
    Attachment 838
    The real servos finally arrived! here is the Hi-Tech HS-805BB Mega Giant Scale Servo being tested. I simply attached one of the many great horns and plates that it comes with to my fish-line spool, using its own screw and voilà! 19.8 / 24.7 kg*cm (4.8V/6V) of torque! It is temporarily held in place with straps as you can see because as you can imagine the square holes of the Vex plates don't line up with anything but their own stuff (I promised I would stop bitching about it!)

    For the rest of the controls I am using the HS-645MG UltraTorque Metal Gear Servos that have 7.7 / 9.6 kg*cm (4.8V/6V) of torque, very much on the safe side.

    On the left of the picture you see Vex's red optical encoder which I planned to use to determine the position of the continuous rotation motors that lift the arms, but again, not even the extremely versatile Make controller could recognize the simple signal. I am sure it can be done but why waste time. I ordered a set of high-res 10 turn potentiometers that are not only more precise but can "hold" the last position value even when the power is turned off.

    The Exoskeleton

    I have been literally immersed in a virtual reality. Working at a small scale forces you to adjust your senses and perception of self. Then you suddenly realize that somehow your fingers are too big, your body too clumsy, your eyesight not good enough to deal with a Lilliputian world. Fortunately our cyborgian self comes to the rescue and we make use of the many attachments and extensions that makes us makers of things, creators of our own destiny. (I might believe that someday...)

    All the mechanics are functioning, at least by hand and in individual servo tests. It has been very hard to deal with some problems, most of which have to do with balance and friction, not of the marionette which is very fine, thank you, but of the mechanical elevator that raises and lowers most of the machinery so that the head can turn, the body express and the arms move while at the same time the Creator changes its position , kneel, stand up etc.

    This problem is not so evident at first, specially if you are used to manipulate a puppet or marionette. Since your hand has a mind of its own it is hard to consciously realize tha amount of intelligence that it has to deal with all these complicated maneuvers. As you move the "plane" controller, pull the strings etc, you hand raises and lowers automatically and compensates this movement by tilting, rolling or yawing the controller.

    Attachment 843Attachment 842
    Potentiometer as high precision encoder

    However, when you have a fixed structure that supports the controllers it becomes evident that you need more than one motor to actuate on any given movement, because each movement influences the rest. Of course, as Dwiggins taught us, you should let gravity do most of the work, since she knows all about the laws of physics, but then there is the issue of correspondance, economy, efficiency and why not, elegance of design. Simpler is better. The complexity of simplicity.

    Attachment 841Attachment 840Attachment 839
    Detail of the servo with its sturdy mounting plate
    Assembled arm control with lead counterweight
    Lead counterweight and potentiometer encoder
    Last edited by sunithaya; 12-06-2008 at 02:59 PM.
    You never change things by fighting the existing reality. To change
    something, build a new model that makes the existing model obsolete.

    --R. Buckminster Fuller

  6. #16
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    Re: Robotic Marionette

    Sense and Sensibility

    Attachment 863
    Visualizing the user interface for servo control

    The nervous system is the current step (by step). Working on the sensors and on the beacons has given me a clearer understanding that there is nothing I know. Still very very far from The Docta Ignorantia.

    Here is our microprocessor stack composed of two Make boards which were our final choice. The boards are highly integrated, very easy to interface and simply well designed. The only drawback was the limitation of 4 servo ports per board. I decided early on that 8 motors were as many as I wanted to use, both for practical and symbolic reasons. Four is the symbol of man generated by the trilogy which comes from the duality contained in the unity (bear with me, it is a stream of thought). 8 represents the power of the king in chess, and the queen in all her potency and (coming down to earth), I could only afford two Make controllers anyway! So, there. I had to do it with only 8 motors, period.

    Then came the IR beacon circuit. That was a lot of fun to build although it took a lot of trial and error to do it with kitchen stuff. DYI instructions stipulate in no uncertain terms that you should use glossy inkjet paper and ONLY print with a laser printer, then iron transfer into the copper plate. Well, after many frustrating trials, botched plates and burnt fingers we (Philip and I) decided to try what you are not supposed to do. Went to our local print shop and had the circuit printed on their glossiest color laser paper with their fancy color printers. That worked beautifully. It transfered absolutely perfect the first time around. The entire coating of the paper stuck to the plate, and I am sure more than one has though that was wrong, but after soaking it in warm water the paper peeled off like a decal and left an impecable mask.

    So here is my friend Philip, which was the instigator of the whole DYI circuit idea cooking up the circuit with a coctel of muriatic acid mixed with hydrogen peroxide. In a few minutes our circuit was done. As usual he is multitasking with his totally hacked IPhone.

    After dealing with the obvious and easy choices, like the arms (4 motors there) I realized the problem. My monster servo would lower the body, yes. But what about the head?, the shoulder strings? (they allow the marionette to turn the upper part of the body to face in another direction). They had to be lowered at the same time! otherwise I would need many more motors and complex programming to synchronize all these elements.

    So the idea of the elevator was born, with all its ancillary problems, weight, friction, balance, stability, randomness, etc. At first I built tracks to guide the (square!) rods up and down. These rods (quads?) support a platform that houses the 3 remaining servos. The problem is that the head has more than one degree of freedom of course. It not only has to turn left and right, it also has to tilt sideways and bow as well. Or pitch, yaw and roll if you will.

    All these simple motions are trivial (if difficult to master) in a marionette. Then I had the shoulder controls to turn the body around; how to do all that with 3 servos and control the wanted nuances?

    After about two weeks of anguish I stumbled upon the solution, where but in a dream!. It is pretty obvious that we work as hard in our oneiric universe as we do in our waking world.

    Next morning I skeptically went to examine the contraption with the suspicion that, like many other "great ideas" conceived in la-la land it would turn to be impractical, impossible or just plain turdy. It actually took me a while to connect my ideas with the reality of the mechanics, something was missing which I had apparently forgotten. Then, all of a sudden I saw it! make one of the servos perform double duty.

    I cannot even explain how I visualized it. It was so obvious, simple, and yes, elegant. The only bummer is that I feel it did not come from me but from the collective unconscious debris. I just picked up the pieces.

    I will post some pictures to explain how it works.

    Here it is:
    Attachment 1013

    How to solve it

    My apologies to George Pólya for quoting the title of his jewel of a book, but "How to solve it" made an indelible impression on me when I read it decades ago. I wish I had had him as my math teacher instead of the monster that expelled me from his class for having the nerve to record his "lectures" (which I did not understand) in what must have been one of the earliest portable recorders (the size of a worker's box lunch) that my dad, a very forward thinking man gave me as a present so I could use technology to help me in my studies. This wicked teacher foamed (he became redder than he was and I remember his veins bulging in his neck) that my intent was to make money with his awful expositions, when my only intention was to listen to it again at home and review the parts that were unintelligible to me. Remember it was the time (1960's) of slide rulers and solving logarithms, square roots etc. with pen and paper! and teachers which threw solid wooden rulers at students if they failed to pay attention.

    In any case, this is how I went about it:

    The two control strings for the head (1 and 4) allow it to not only turn left and right, but as I said before to tilt sideways and bow as well. In a traditional marionette these strings are played like an instrument, varying the tension, twisting and plucking.

    When the marionette needs to kneel or jump etc. you are not really concerned with this since the entire body, head and all is balanced by your hand, which uses your own personal embedded experience as a subject of gravity to effect movements which prove extremely hard to program convincingly. Imagine for example that you want the character to tilt his head slightly in an inquisitive way while bowing and kneeling at the same time. If you try to break that into individual movements performed by individual muscles of your hand, fingers and arm you will picture the complexity of the apparent simplicity. Don't forget that I said tilt his head in an inquisitive way!

    So, in my dream I must have followed some of the principles Pólya suggests to poor souls in distress, like for example:

    • Look for a pattern
    • Draw a picture
    • Solve a simpler problem
    • Use a model
    • Work backward
    • Use a formula
    • Be ingenious

    The 'head' strings reach the horn which would turn the head left and right and you would think that is where the strings should end. Then I visualized (and this is what comes from the dream) that the strings at that point corresponded to my left hand fingers twisting them while my right hand controlled the other movements in unison.

    So I let the strings continue on to the other 'hand' which would pull or let go to let the gravity do its thing. The combination of these elements (including the most important, gravity) give you a very rich and expressive palette of head "language". This of course I cannot convey simply by pictures, but I will eventually post a video of the movements.
    Attachment 870
    The 'other hand'

    I continued raiding my wife's sewing supplies and used this perfect and beautiful spool, which I epoxied to the servo horn (you can still see behind the spool the gray irregular shape of the rock hard Apoxie that I used. Need to refine that.)

    There was another problem, which because of its apparent simplicity tends to be forgotten until it is too late. Remember the analogy with a string instrument. So it is that you must tune the strings of your marionette to the perfect tension which allows precise control while at the same time giving gravity and inertia room to infuse the movement with the illusion of life.

    Easier said than done. First of all the strings are very thin and usually waxed or Teflon coated to prevent fraying. That makes tying and untying knots practically impossible. Then consider the awkward and tight places where the strings are connected. Finally, size. Things that are very easy at a human scale become wickedly difficult in Lilliput.

    Attachment 866
    Bowl of Sushi by Hiroshige (Edo Period)

    My love of sushi came to the rescue. Chopsticks! the bamboo sticks have the right diameter, are pleasant to touch and sight (and taste) and its transversal structure provides the friction necessary to prevent the 80 lb. Teflon string from sliding. This was my prototype but although it stopped that string diameter from sliding, my preferred string is .006" Fireline, which is a braided bead thread very strong and resistant to abrasion (it is used to weave the smallest glass beads). This string just went through my tensioner like a water snake.

    So I refined my prototype incorporating an opposing path that effectively holds it in place. And what is more important and the reason for this exercise, it is easy to adjust as needed, to tune the strings of the instrument.
    Attachment 868Attachment 867
    Tension is good when needed
    Last edited by sunithaya; 01-12-2009 at 01:43 AM.
    You never change things by fighting the existing reality. To change
    something, build a new model that makes the existing model obsolete.

    --R. Buckminster Fuller

  7. #17
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    Gainesville, Florida
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    Re: Robotic Marionette

    IR Beacon

    Attachment 878
    This is the first finished beacon to be worn by the performer on stage. This will be tracked by an overhead camera to detect the position on a grid. It has 24 IR (infrared) LED's. The idea was that, since the tracking camera must have a wide angle in order to see the entire stage from above, we needed an array big enough that would be easily tracked.

    What I did not realize was that the angle of the LED's that I got was extremely narrow, so that when the performer lowers or tilts her head (the beacon is on top of her head) the LED's practically disappear. So we came up with the idea of using a diffusion dome to spread the light. That of course is half a ping-pong ball which happened to have the exact required diameter.

    The ball was too thick and did not let enough light through, so I sanded it until it felt like a turtle egg, if you ever touched one. The solution worked, however there was still a considerable loss of light.

    So I started to look for new LED's. This time I made sure that the lens of the LED would be wide enough to allow the free movement of the performer's head. This is what I found:

    Ultra Wide Angle IR 850nm

    These LED's are awesome. We could not believe how wide they emit light and how bright they are. You can almost turn the away from the camera and you can still see them!. So they will definitely do the trick without the need for a diffuser. We will use a set of ten which has the added benefit of resulting in a much smaller device and, because it is IR, it will be invisible to the audience.

    I bought them fromthe guys at NaturalPoint which have a wide (yes, intended) variety of optical devices, mostly for motion-tracking. A set of ten cost me US$ 15 which is about half of the price of "cheap" LED's at RadioCrap.

    So now we will design and burn another circuit and probably use a coin battery instead, to make everything really compact and unobtrusive to wear.

    As soon as the user interface is ready for the tracking and motion-assigning program I will post pics of the UI and the tracking screen which is a lot of fun to see in operation.

    Chicken Coop

    After thinking for what seemed years, about what the material for the background for the stage should be I decided to use something called "hardware cloth". I must admit I had never heard such term until I described what I wanted to a person I know at my local Loew's store. He immediately said, "you want hardware cloth", I said "no it must be metallic!". So he simply lead me to the garden area and noted that it was just a sort of "chicken wire". So that was exactly what I wanted, but did not know the name, so now you know too.

    It is pretty sharp and can cut you very nicely if you are not careful. I did not use gloves because I had to bend the ends and the gloves prevented that, so it took quite a while to do it without bleeding to chicken death.
    Here it is already cut and tried for a good fit. I like how it seems a natural fit to the rest of the stage. The idea is that not only supports the materials and "stuff" that I will put there, but it also acts as a grid with all the connotations that the word has in terms of media. Once I project from behind (over a translucent substrate) it will look, or so I hope, as a kind of coarsely pixilated environment, very apropos with the theme.
    Last edited by sunithaya; 12-06-2008 at 06:21 PM.
    You never change things by fighting the existing reality. To change
    something, build a new model that makes the existing model obsolete.

    --R. Buckminster Fuller

  8. Re: Robotic Marionette

    This is extremely interesting mate, very very inspirational! Could you post a video of the mannequin in action?
    Edit: you mentioned the Make Controller had only 4 servo ports, you definitly shoudlve gone with the Axon MCU by John and it has 55 I/O ports and is $130, while I think the two Make MCUs were $80 each?
    Last edited by No0bert; 12-06-2008 at 10:36 PM.

  9. #19
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    Re: Robotic Marionette

    Thanks No0bert, this is what I like so much about this forum, where people actually share their knowledge and information with others. It reminds me of the early computer clubs where everyone would show their latest invention. Of course all that has changed and lawyers make sure you don't spill any beans if you have a potentially profitable idea!

    I will post a video for sure, but I want to go through my entire process to get there because I learned quite a few things along the way and I think it might help others. I will look into the controllers you mention. I have controllers that can handle many servos but one of the reasons I chose MAKE is that it works seamlessly with FlashDevelop which was our development environment (and if people don't yet use it I can't recommend it enough). You will see later on when I post the program which of course its not and never will be finished! but as I think I said in an earlier post we will release it as open source through CC (Creative Commons) so that everyone can use it. But I am not there yet...few more posts down the line:-)
    Last edited by sunithaya; 12-07-2008 at 01:15 AM.
    You never change things by fighting the existing reality. To change
    something, build a new model that makes the existing model obsolete.

    --R. Buckminster Fuller

  10. #20
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    Nov 2008
    Gainesville, Florida
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    Re: Robotic Marionette


    This is a little digression which however might clarify the weirdness of it all

    I tell all this (and there is so much more to tell) because my childhood was, among everything else I know and care about, the root and the source of my current work. In that privileged environment where the fruit of our labor and our play (is there any difference?) both fed us and entertained us, I learned to make my first puppets and my first theater. My audience (beside my grandmother) were the three or four kids that survived in the vicinity of our house.

    Nowadays it has become fashionable to "go green", like trying to patch a dam when it is about to burst. We have forgotten how, not too long ago, recycling was for many simply a way of life. But perhaps that is just because some of us grew up in a very different circumstance. People today would say that we lived in misery or poverty, therefore we were forced to straighten a bent rusted nail instead of simply buying a new one.

    For me that was what made my life extraordinary. My grandmother, who had taken a "poverty vow" (go explain that to someone living in a consumer society!) lived a life where everything around her had a purpose and had to be taken care of. Since I grew up with her it was natural for me to learn and understand how to create with what the world around me, particularly our shelter, provided. To what others was a miserable shack, to me was a magnificent castle, full of adventure and stories, constantly morphing through the tension between entropy and our creative survival.
    You never change things by fighting the existing reality. To change
    something, build a new model that makes the existing model obsolete.

    --R. Buckminster Fuller

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