2011-10-14 19.42.09

I have taken some photos of my new version of my "limb embiggener" where I've uses bolts instead of fabric tape for the joints.

It still seems much easier then the original skeletonics system that inspired me, and more sturdy than my previous mechanical arm. Hopefully there's enough information to give anyone a good start to making one.

The Perth Artifactory had all the tools I needed - drill press, saw, clamps, measuring tape.

I bought some more bamboo and some long bolts, I think 3/8 inch diameter as the metric ones at Bunnings seemed either too wide or too short, cut some bamboo, drilled the holes in the bamboo, big enough for the bolts to go through either easily or with a push, and fit it all together.

Taped on the bicycle brake from the previous arm, originally from a local bike shop, to be the claw.

The holes through the bamboo were sometimes visibly misaligned, so when I laid the bamboo down with one hole vertical, the other was off vertical. I may have had to widen a hole now and then to give it enough slack to cope with the misalignment, and but generally it seemed remarkably tolerant of my errors.

To wear it, I strap it onto my arm with double-sided velcro - the stuff with hooks on one side and loops on the other.

All my mechanical arm pictures on flickr:

Tensegrity: one of the principles I used in designing it - each length of bamboo should be under compression or tension only, it should not be under significant bending stress. Where it was, I reinforced it with pieces to take the load as compression and tension instead. That's basically how I added the triangles.

There is still a bit more reinforcement that could be done, but it would just help take the weight of parts of the arm, not whatever load is held with the claw.

Some of the bolts stick out a fair bit, so I have to be careful not to scratch things or myself with them by accident.
The top google search result for limb embiggener was this picture of my unpowered exoskeleton arm!
Extendor Articulated Bamboo Exoskeleton Limb Embiggener

But since seeing Ghost in the Shell I now want four wheeled limbs like the Tachikoma's legs.
Read more... )
Ever since Peter Hillier showed me the youtube video Skeletonics showing an unpowered mechanical exoskeleton that roughly doubles the wearer's reach I've wanted something like that.

However I wanted it to be cheaper and quicker to make. I am starting with just a single arm. My first version was a roughly 0.5 scale prototype made from plastic straws held together with sticky tape at both the plain joints and the rotating joints. It worked remarkably well initially though the sticky tape joins didn't last that long. I think it took well under an hour to make.

My second version was made from bamboo with bamboo sticks as the rods ($4.60 at Bunnings for more than I've used so far), cloth tape for the joins, and a $26 worth of bicycle brake parts to substitute for a hand. It took maybe 4 hours to make at the Perth Artifactory which had clamps and saws to cut the bamboo to length.

Issues with the current version:
The bicycle brake hand has a very limited range of motion. But it can still grip a can of soft drink.
With no straps yet, I have to hold the shoulder joint in place with the other hand.
The cloth tape keeps coming loose.
Some of the joints need to be quite loose for the sticks to be able to rotate past each other.

Well I've made the straw version and the stick version, if this is the three little pigs the next version should be made of brick. Unfortunately it's too heavy and brittle.

Possible upgrades:
Straps so it's attached to my arm instead of just held by hand.
Bolts through drilled holes instead of cloth tape. This will require adjusting the design so the rods stay out of each others' way.
Aluminium tubes instead of bamboo. The bamboo's worked pretty well so far though.
Cover the mechanism so it looks more solid. Could use metal foil or fabric.
Also I should get some more pictures up online. Jason put a video of me lifting a drink bottle with the arm here

I haven't worked out how I'm going to upgrade the hand yet. It may end up being more work and than the whole rest of the arm, it's already the most expensive part.



October 2011

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