home  >  Icarus < Liberator > Timbug-II 23 May 2010

Shadow Liberator - by David Buckley

  • Liberator Explained

    Early on in the development of the Shadow Biped Walker there were several people who wanted to work on an intelligent hand eye system but it was clear that it would be some time before the walker would be a suitable platform.

    With that in mind I designed Liberator so that work on vision could proceed using a basically human shaped robot, it takes up about the same floor space as a human and with a camera mounted on the top would be about 5ft 2in tall (no eyes of blue though, yet!). A shoulder plate mounted on the top of a thin body provides a mounting point for experimental arms. It was designed to unbolt into sections so I could get it into my car.

    Our previous vision guided robots had crawled about on the floor attached to a computer by an umbilical which also supplied power and as everybody knows (sooner or later) umbilicals just get tied in knots, wrapped round wheels, get caught in things, you think of it - it happens. So Liberator had to be self contained. The plan was to transmit the video signals to a receiver attached to a computer, get the computer to figure out what to do and send the control signals back to liberator, however that part never got built and so for higher level processing Liberator still needs to have an umbilical.

    Today Liberator consists of a base unit with two drive wheels and two castors in a wheelchair arrangement. The two motors came from Autopolisher units (from Halfords?) and each drive a wheel through a toothed belt reduction drive, power is supplied from a 12volt 20Ah sealed lead acid battery positioned between the drive wheels. Also on board is the necessary battery charger and a distribution panel with switches and fuses etc. Around the perimeter of the base are sensor plates through which Liberator can detect if it is touching something. Originally the computer was mounted on top of the base unit but it was moved to above the shoulder plate because I got fed up of crawling on my knees during software development. All the body is made from WOOD. Wood is an insulator, you can glue it, screw it, nail it (not advised), paint it, and saw it and drill holes in it and otherwise shape it without worrying about the dust shorting out the electrics.

    The controlling computer is a Triangle Digital Services 2020 16bit ANSI Forth computer which communicates with the base hardware via an I2C bus, the motors are pwm controlled and each drive wheel is fitted with an encoder disk for feedback.

    At the moment Liberator is quite happy wandering aimlessly round the lab but really needs someone who will spend some time on improvements.

    In the background can be seen the Shadow Walker (on the right and Dan! on the left).

    David Buckley - 1994

    [above photographs of the Shadow Liberator by Richard Greenhill]

    For more information see http://www.shadow.org.uk/projects/liberator.shtml

    July 2008, Liberator as the result of some intern attempting to fit Ultrasonic sensors!
    Even the drive belts to the shaft-encoders for the wheels have been destroyed and one has been replaced by rubber bands. Sigh.

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