Intro: Hand Built Humanoid Robots, Part1: Introduction
Almost all humanoid robots large enough to be useful in a domestic setting are still built using a technology originally developed for car-welding factory robots - ultra-rigid metal bodies driven by super-precise electric motors.
This is why a robot moves like a robot - or like someone doing the the robot dance: http://www.youtube.com/watch?v=4YJ3BTKMILw
But whilst a human can imitate a robot, a robot cannot imitate a human, why? because those super-precise motors must always be switched on, always be engaged and always in total and absolute control of the exact movements of the robot - in short, it cannot relax.
This doesn't sound like a big deal.
But when you combine that with an ultra-rigid body it makes life very difficult indeed if you're a robot trying to clean the average home. Any error of judgement and that ultra-rigid arm is going to be super-precisely put through that glass tabletop.
Just a bump in the rug is enough to make the robot a few degrees off from where it calculated it was and bye-bye glass. This problem is fundamental to the factory robot approach because speeding up the reaction times enough to avert the accident also increases the potential damage that can be caused and slowing it down enough to never make mistakes renders the robot useless.
Factory robots rely on the closely controlled environment of the factory to operate at speed - saftey barriers and all. Take that away and they are just chunks of metal destroying the soft furnishings.
Picture yourself running past the glass table and picking the same juice glass up. You can do this because your body is elastic and by relaxing the right bits your hand can easily be made to skim along the surface of the table without damaging it.
This very simple difference makes all the difference.
You do not have to know precisely where the tabletop is, your little finger can find it and guide your arm along it as quick as you like because the muscles of your arm, back and shoulder can stretch to accommodate any errors.
So it's simple right? just add elasticity to an ultra-rigid factory robot and surely it could do the same thing? Well no, because then it's no longer ultra-rigid, and that means your super-precise motors no longer know where they have just moved the robot to.
So you start adding springs and extra position sensors and force sensors and acceleration sensors and soon it's nothing like a robot you understand or have ever seen before. In fact, it seems to work a lot more like a biological system - and fortunately there are lots of working examples of humanoid biological systems to study - us.
One day we may be able to engineer it better, but for now we are still struggling to understand just why the human body is put together the way it is and how this gives rise to the incredible feats we are capable of: http://www.youtube.com/watch?v=Vo0Cazxj_yc
What we present here and in the following instructables is our method to attempt to solve this riddle by building a succession of androids with bodies that function, as near as we can manage, by the same mechanical principles as our own.
The aim is to produce engineered copies of the internal mechanical anatomy and materials of the body. Everything from functioning copies of the low friction surfaces of the joints to the patterns of muscles with motor driven tendons connected elastically in the same locations and manner as the real muscles.
This all sounds well and good but surely it's very expensive? Well, yes and no.
It's certainly been expensive developing how to do this and we've been lucky enough to have a couple of grants along the way but oddly the robots pictured below were entirely built by hand from relatively cheap components with simple hand tools - salvaged screwdriver motors, speed controllers for R/C cars and homebrew microprocessor boards.
Total cost: <3000 $/Eur
(Approximate: 46 screwdriver motors x 15 $/Eur, 46 potentiometers x 10 $/Eur, 46 speed controllers x 27 $/Eur, 6 microprocessor boards x 30 $/Eur 5 kilos Shapelock (Polymorph) 100 $/Eur, Dyneema, webcam, speakers and other materials < 300 $/Eur, )
3k of bits for a full-size, functioning robot humanoid torso with 46 powered degrees of freedom, laptop not included...
Whilst that's chicken feed next to the 400k for a PR2 it's still more than most people's pocket money, but fear not, for under a hundred you can still make yourself a very respectable pair of hands.
So, let's get started.
The most important ingredient is Shapelock (Polymorph in Europe) which is used to hold everything else together and you can get an almost free sample (P&P) to play with here:
Shapelock sample: http://shapelock.com/page3.html
To really get the most out of it though you're gonna need a few more things...just the list below is enough to make a pair of fully working hands.
Shapelock (Polymorph) - the standard white stuff, a finger uses 10 to 15g
High performance string - this is for tendons so the stronger the better, Dyneema is the best and is used in fishing, sports and camping so should easy to find - 1.5 to 2mm diameter is plenty strong enough, allow 1m per finger
Bungee shock cord - the good stuff is marine grade for boats - 3 to 4mm diameter by 4cm per finger
Superglue - a slow setting gel type is much easier to handle, one tube will do dozens of fingers
Cold spray - also known as freeze spray, ice spray and instant cold spray, one can of the kind sold in plumbers stores should be fine
Teflon - a single bicycle gear cable liner or a packet of self-adhesive Teflon sheet (the type backed with a thin layer of double sided foam, not the thick heavy duty ones with a layer of solid rubber) as used for furniture sliders
Lycra - as used in sports gear, the stretchier the better, allow 10x10cm per finger
Aluminium tube, round - about 12mm or 1/2" diameter by 1m
Kitchen bowl - capable of holding freshly boiled water, glass is best so you can see the Shapelock (Polymorph) melting
Kettle - any will do
Microwave oven - any will do
Hot air gun - as used for paint stripping
Non-stick rolling mat - any cheap silicone rolling mat for pastry should be fine, Ikea also sell a transparent polypropylene work mat which is perfect and at a push the lid of a good size tupperware will do
Non-stick rolling pin - any cheap silicone rolling pin for pastry should be fine
Small piece of aluminium sheet - used for rolling out sausages of material, again you can get away with using a tupperware lid
Scissors - if you're using Dyneema get special Dyneema cutting scissors, no really
Side cutters - an old blunt pair is actually best
Pliers - the more leverage the better
Soldering iron - the soldering gun made by Weller gives much better control than a standard soldering iron
Once you've got all these things together it's time for Part 2: A primer on Shapelock (Polymorph) swiftly followed by Part 3: How to make a robot hand