Decal Evolved-Composite Application Layer for robotics

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Robotics is as subject to the laws of industrial economy as any other system. Components shrink and integrate leaving little more than a network of motors sensors and processors connected by cables and substrate.

Decal evolves the concept into an application layer containing the processors, sensors, plus a template, adhesive and aesthetics in one module that applies to corrugated cardboard, polystyrene, PVC foams, Balsa and similar compressible sheet materials.

Further to the concept of #Cardware, DECAL leverages environmental resources for construction. Many lessons have been learned from the project.

  • Complex folds and numerous tabs to locate are gone

DECAL uses laminar material geometry for structural integrity. Surfaces are now formed from a flexible exoshell bonded to a foamed substrate that is then curved to compress the foam against the shell, making it rigid.

  • Glue is gone

The system includes all the adhesive required. Parts just require forming into a curve and joining with a single pre-glued tab after cutting around them.

  • Complex wiring is gone

Use of foils and ribbons and integrated circuits in a single layer make construction simple and easily transferable to many materials without a retool.

  • Hard to find card stock is gone

DECAL uses inexpensive manufacturing processes and builds on even cheaper resources, but looks more professional and contains many improvements to Cardware's philosophy. It is also a lot more durable for the same weight than card stock and has a cleanable surface.

DECAL's composite architecture goes under the hammer.

Working out the geometry

The complicated hip unit from cardware reduced to its bare minimum now assembles in two operations - form the templated material into a circle and reinforce the cylindrical shape with a cross-brace. Using a foam against a curved surface braces it in all directions, stiffening the surface and increasing the density of the material at no cost to weight.

DECAL's adhesive sandwich

Construction is simple; layers of material and adhesive bonded together are cheap and easy to assemble and as an end product can be supplied as a wallet of stickers and foam shapes and a bag of servos and screws.

Proper terminators for the sensor cables would be nice.

Circuitry can be built into the stickers by adding an etching stage for the foil, then soldering in SMD components before laminating. Things like LEDs and surface connectors for the wiring harness on the limbs can be interfaced to surface-mounted processors using a breakout: This has a 0.1" pitch edge connector and double-sided tape to bond it to DECAL's laminar circuitry, plus a standard 0.1" Dupont header for the servos. Sensor buses in orange and green, servo bus in blue. C1 and R2 are a filter for ARef.

Hacking SMD into Decal

I wonder if 0.1" Plated Half-Hole edge connectors in purple are even possible? :-)

Servos attach to the system via screws that go through the shell and fix into the mounting flanges. Simple, and sturdy.

I've also paid close attention to the way that the system looks and moves. Servos have a throw of around 190 degrees and DECAL accommodates this where Cardware could not, I managed to squeak around 170 degrees from the cardstock version and had trouble with positively locating the artwork with the template because its double-sided and domestic printers are not very good at registering the paper for multi-pass prints. Here they are combined into one print, avoiding the problem altogther.

Integrating the template and artwork together also means I can use photographic resources and skin the shapes properly, previously the artwork was planar and vanished into folds and cutouts in the design.

Snake Hips

I chose the skin design because I used to have a Ghost Reticulated Python and it caught my eye while browsing for Internet of Condoms' Kooga print, before I found the fabric itself.

Who wouldnt want a walking Python, I so very nearly called the project BOA Constructor XD

  • 1 × Compressible Sheet Materials Polystyrene, Corrugated Cardboard, PVC Foam, Balsa...
  • 1 × Clear Sticky Backed Plastic Or with a pre-printed pattern
  • 1 × Copy Paper Not needed if patterned sticky-back plastic is used
  • 1 × Conductive Foil / Foil Tape Aluminium, copper etc
  • 1 × Ribbon Cable 5 Way Ribbon

View all 6 components

  • DECAL From Scratch

    Morning.Star9 hours ago 0 comments

    About 6 hours uninterrupted hacking.

    While Bea is on respite for a few days I can put linear hours into building and concentrate fully on what I'm doing. I only get this once a month so I make the most of it.

    I decided to build a limb from scratch, photograph the templated parts and then video the final assembly. I'm also working on a better foot, I'm not happy with it and it needs another servo in the ankle anyway.

    Laminating the printed skin with transparent plastic...

    Cutting out the templated parts in sections for their procedures...

    Adhesive goes on the bracing parts directly, they dont have any active circuitry...

    So they attach straight to the polystyrene...

    And can be cut out with a pair of scissors, then glued together with their own adhesive patches...

    The finished cross brace parts...

    Servo mounts and integrated connectors get the same treatment, they attach directly to the skin...

    Then cut them out ready...

    And add solderable connectors using double-sided tape... I've used Polyethylene for the bearers themselves, superglue wont touch it.

    Connections to the front face are accomplished with a strip of copper... The horizontal foils are isolated from each other, they are covered with sellotape first and then the vertical foil covers that for shielding. I only want the horizontal faces to be visible from the outside to body fields, the 'cables' will interfere so they are behind an isolated foil.

    The through-connectors are then soldered together with the front face connection. This wont be necessary when the new tape arrives, just lap it and the adhesive takes care of the circuit...

    This is then covered with sellotape to isolate it from the next foil and so on.

    ... Lunch ...

  • Flexibility

    Morning.Star3 days ago 2 comments

    Turns out I wont need to use cabling. According to Hackchat, OSHPark are in the process of rolling out flexible PCBs, an exciting development well suited to DECAL's architecture for a production run.

    Meantime, it gave me an idea. Instead of messing about with ribbon cable connections, and trying to stuff a lot of cores through each successive joint on a limb I could go directly to flexible circuit, which would also allow me to spread the components into the limbs more easily.

    A little bit of research tells me flex PCB is no more than Kapton and copper foil with a bit of etching. I can easily obtain small quantities of both Kapton tape and copper foil tape from eBay, and I have etching fluid and photo-resist spray, transparencies and an exposure box.

    It shouldnt be too hard to create the limb parts so they solder together in a line. Using a single ribbon this way means I can run it up the limb on the servo actuator side and put an S in it beside each servo with enough slack to allow the joint to flex. From experience I know this configuration will stay tidily inside the joint axis; it's the same as the flex connectors in all manner of equipment with shuttles, like CD players and floppy drives.

    Hacking Copper

    I've got loads of aluminium foil tape, which is easier to get hold of than copper foil, and a lot cheaper. The only problem with it is you cant solder to it. Well, you can, but it needs a bit of tricksy chemistry to get the solder to alloy with the aluminium.

    Turns out this doesnt work on aluminium however it does work on things like nickel and brass. Alu forms an oxide layer faster than the copper is laid down and the result is small beads of copper building up on the surface.

    You can see the plating building up in the bead. I got quite excited at this point, about 20 minutes in.

    Unfortunately, after I gave it another 10 just to be sure, it was completely useless. The solder itself broke the beads away when I tried soldering it.

    However I have discovered an alternative. From RapidOnline's documentation:

    Which will make things like this a lot easier.

    Card prototype is solderable, but Kaptan would totally rock. I've been meaning to get some for ages...

    This has 11 layers in it in places... And I managed to clip all of them with the scalpel and shorted the entire thing out cutting the servo port. D'Oh!

  • Stickin it to IT

    Morning.Star3 days ago 0 comments

    I managed to find some decent double-sided tape to experiment with, and it works even better than I expected.

    DIY Badge Engineering:

    Custom Skin

    I had a bit of bother using #TweetyPIE to build the skins with. It uses Python Imaging Library's Transform function which is a pain in the butt to use. For starters I'd need to rewrite it to take a rectangle and produce a polygon, at present it does the opposite.

    It also doesnt handle curves or complex polygons, so I wrote a routine to morph one shape into another and used that to custom-fit the design.

    It is fairly simple, it scans the shape bitmap line by line and finds the drawn portion, then scales the entire source image line to cover it.

    from PIL import Image'decal_im.png')               # get the source image bitmap
    srcmap1=srcim1.load()                           # get the source pixmap into an array'decal_sh.png')               # get the source shape bitmap
    srcmap2=srcim2.load()                           # get the source pixmap into an array
    W,H=srcim1.size                                 # get the width and height'RGBA',(W,H),'black')           # make a new image to hold the curved copy
    dstmap=dstim.load()                             # get the dest pixmap into an array
    for y in range(H):                              # iterate rows
      x1=0.0                                        # reset left edge to left border
      while srcmap2[x1,y][:3]==(0,0,0) and x1<W-1:  # look right for black pixels;
         x1=x1+1                                    # if a black pixel increment left edge
      x2=W-1.0                                      # reset right edge to right border
      while srcmap2[x2,y][:3]==(0,0,0) and x2>=x1:  # look left for black pixels;
        x2=x2-1                                     # if found decrement right edge
      if x1<W-1 and x1<>x2:                         # avoid empty lines
        dw=x2-x1                                    # difference in width between borders and edges
        c=1.0/(W/dw)                                # coefficient of this
        for n in range(W):                          # iterate columns
          dx=(c*n)+x1                               # calculate new position of pixel
          if dx<=W and dx>0:                        # if the coords are valid
            r1,g1,b1,a1=dstmap[dx,y]                # get the pixel at the destination
            r2,g2,b2,a2=srcmap1[n,y]                # get the pixel at the source
            r=r1|r2                                 # binary or them together
            dstmap[dx,dy]=(r,g,b,255)               # write the dest pixel'decal_cmp.png')                     # save the composited image

  • BOA 367

    Morning.Star06/19/2017 at 13:40 0 comments

    I've accidentally found a name for the robot I'm building using DECAL.

    BOA isnt a snake tho. It stands on two legs to walk, so its going to need feet...

    This is a major departure from the other parts I've done, so its a bit experimental. I've worked out geometry for the limbs already with Cardware, so I'm trying to match the style.

    Each foot stands up on three toes, two at the front and one at the back. I had the idea to make it springy under the weight of the robot, but I suspect it will be only marginally so. The two layers are already very stiff, with a layer of PVA creating a stress across the arch it doesnt bend at all.

    There is also another layer tensioning the arch underneath. This does a better job than the PVA which relaxes a little. I'll replace this with a layer of double-sided tape which will be an instant and solid fix.

    The hinge mechanism to stabilise the joints turned out to be easy too, although will require a little bit of engineering to make a bearing that mates with the laminar adhesive. I've used a Felting Nail, cut down and glued in line with the servo actuator shaft on the inside of the leg section.

    It still needs a bit of tube glued into the hip section so it doesnt wear away the polystyrene there.

    Note the light catching the polymer skin makes the scales look disturbingly arterial with the cabling underneath. I wont make any jokes about serpentine blood supply, I promise. ;-)

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Adam Vadala-Roth wrote 06/18/2017 at 17:11 point

interesting concept, is it sort of like those ants that festo made with the painted on PCB on the surface of the exoskeleton?

  Are you sure? yes | no

Morning.Star wrote 06/19/2017 at 00:38 point

Hey Adam :-)
I have no idea, I've only seen photos of those things. Probably not, Festo are into chimerae, I'm trying something that never existed before for the competition. However I realised what I'd done was transferable to other materials, and modular, so although this one is a robot, its also a paradigm like Cardware, an application. Wearing snakeskin boots ;-)

  Are you sure? yes | no

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