Oct 18 2010

Robot Tentacle Arm – First Steps…well, wiggles


I’m quite interested in robots with organic movement, the sort of thing that looks creepy due to its unnatural naturalness and with this in mind I’ve started looking into building a robotic/animatronic tentacle arm (Japanese schoolgirls beware!). My first step was to have a look at the sort of thing floating about on youtube already, I’ve compiled some of the best examples into a playlist.

The basic structure seems to be a set of ribs with guide holes for wires, spaced along the length of a flexible tube. Control wires run up through the ribs and are tied off at the end of the arm so that when they are pulled at the base the arm flexes outward toward the side that the cable is on. To get a feel for the workings I decided to knock up my own simple version using cardboard ribs and 3 control wires. I made the template rib shown below and copied it multiple times to fill a sheet of A4 paper (print @ 300dpi for correct scaling).

Segment template for tentacle arm

Rib segment template

I printed out my page of ribs and glued it down to some scrap cardboard, then I cut out 8 or so (I would have done more but got bored). Once I had a stack of arm segments I looked around for something suitable to use as the flexible core, the first thing that came to hand was the inner tube of an old biro laying on my desk. I made holes in all the rib segments using a pin and scissors, then started to thread them onto my biro core. To keep the segments separated I cut short (15mm approx.) lengths of clear plastic air tubing, the sort used in fish tanks. These fitted snugly over the core and were stiff enough to add strength to the arm.

Once I’d stacked up as many segments as would fit (7), I cut 3 lengths of fishing line and ran them up through the ribs to the top end of the pen, where I tied a simple slipknot in the end of each piece and tightened them over the biro. To hold the whole lot vertical I simply clamped the biro tube in a small vice.

I was thinking about making some kind of joystick contraption to control the arm to begin with but after a quick sketch and a cup of tea realised that I was over-thinking things considering the rough state of the arm, and I decided instead to use a marionette style controller made from two pencils taped into a cross shape. I did cut a flat into the middle of each pencil to stop them twisting away from square, but even that might have been overkill. I notched the ends too so that the fishing line could be secured easily, again using slip knots, and that was pretty much it.

The expertly crafted tentacle arm and controller

It works quite well given the simplicity of the setup and has definitely made me want to go on to a slightly more complex version, probably using my CNC machine to cut the next set of ribs from MDF or plywood.

Oct 12 2010

Oogoo Heart Mold


After seeing this article on Hackaday describing an easy to make silicone casting  material I knew I had to give it a quick go.  The photos here show the results of making a mold of a polymer clay heart and then making a heart shaped ice cube from it.

Oogoo is basically equal parts corn flour and sealant, mixed into a white goo.  This Instructable has all the details for making Oogoo and fully documents its many uses.

Mixing Oogoo takes a bit of effort, I used a cardboard tub as a container and an old paintbrush handle to mix with, this probably made it more difficult than it needed to be  but that’s what I had to hand.

Once mixed, i found it quite difficult to spread over my heart form, next time i plan to wear latex gloves and shape it by hand.

Even with my shoddy mixing, crappy tools and less than ideal spreading technique, I ended up with a usable mold in around 2- 3 hours. To test it out, I simply filled it with water and froze it for an hour or two.

As you can see, the Ice heart isn’t perfect, but it’s pretty close.  A definite success!

In future, if I need to make a mold for any reason,  Oogoo is going to be my first port of call, its quick, cheap and absolutely stinks of vinegar. What more could you want?