How to beat the BBC Micro. Pencil tests for about five hundred quid less!
IN THE LAST ISSUE WE DESCRIBED HOW THE BBC MICRO COMPUTER HAS BEEN USED FOR ANIMATING SIMPLE DRAWINGS.
NOW DAVID J.M. COLEMAN TELLS US HIS OWN METHOD OF CAMERALESS ANIMATION.
Yes, forget about modern technology, forget about film and projectors: go back to the last century and build yourself a device on which you can view a sequence of animated drawings as soon as you have drawn them, at any speed you like, and in full colour.
The ZOOTROPE (or ZOETROPE if you look in Chambers’ Dictionary) was a popular children’s toy in Victorian times, and just consists of a drum with vertical slits cut in it at regular intervals, mounted on a spindle so that it can be made to revolve freely when spun by hand. You look through the slits, which take the place of the shutter in your projector at the series of pictures being transported round by the movement of the drum.
My ZOOTROPE is made of stiff card (left over from a film title) and is large enough to take fourteen frames of movement as one sequence, though yours could probably take more (or less).
To make one for yourself, first decide what frame-size you wish to work with – mine is about four by six centimetres (vertical format!) and I don’t think it would be practical go very much bigger than this. Using compasses (for accuracy) for all measurements, mark out on a long strip of paper a row of frames separated by frame-lines the thickness of the slots you want to look through. Mine are about 5 mm, but I think this may be too wide: The wider the slits, the longer the ‘exposure’ in your eye of the picture inside the drum, and the more blurred it therefore looks, but then again, too-narrow slits don’t let much light through to form the image you see. With a bit of trial and error you can find your own compromise between the two!
Leave one slit-length at either end of the strip when you have marked out and cut it out: put mathematically:
Length of strip = n(f + s) + 2s
where f = width of frame
s = width of slit
n = no. of frames
This is the measurement for the (internal) circumference of your drum: cut it out of stiff card as thin as possible (or if you’re a real D.I.Y. maniac, out of sheet metal or thin wood, making it at least 2 times as tall as your frame – but not too tall, as it’s got to balance nicely to be able to turn properly on the spindle.
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