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Last update: 12 July 1999
Copyright (C) 1999 Pitronics

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Designing `Ameba'

Ken Huntington pondered two different shapes for his Egg Hunter. This one no doubt inspired the name `Ameba'. In his own words:
KH: The green rectangles are wheel cutouts; the green circle is the sensor support board; the red lines, sensor wire; the black spheres, sensor common and hold down points; the red spheres, contact points. The top set of sensors, A, D and E hide duplicate sensors such that touching an egg will also be indicated. Sensors A and E may be combined after a couple of tests have been done. The exact hookup has not been determined at this time.
Early Ameba, top view
KH: Ameba does not employ any type of grabber but relies on her shape and uC smarts to first trap, then contain and finally transport an egg to the gathering area. Rollers, fore and aft, work with drive wheels to keep everything stable. There should be enough room on this assembly for the motors, battery, switch data collection circuitry.
Most recent Ameba top view
In the end, this shape became dominant. It should have little difficulty in collecting Eggs, even when in a corner of the Playground (in contact with two walls). Herding an Egg to the gathering corner is another matter. But the most critical paths of this design are the haptic sensors. The wires have to be bent in shape with great precision, and the contacts must be reliable even when lightly touched.
What you see above are two motors of the same type as used by `Jaws' and my Spider (check this photo, and this one). The wheels are micro-cassette recorder flywheels, with o-rings as tires. Navigation is partly based on dead reckoning, enabled by very nice optical commutators in the wheels - the reflective optocouplers are also recycled recorder components.
Here are a motor and wheel with commutator surfaces in place - they are made from aluminum tape, carefully cut into 16 tiny triangles. Quite a job!
Optical commutator
Sub-chassis with two motors and wheels
Two motors fit tightly in Ameba's central sub-chassis.
These .gif images of Ken's drawings don't do them justice at all. If you are able to print Postscript, then click on this front view to download a .ps version of the entire drawing (82K, uncompressed).
Most recent Ameba front view
And what's that pot-like hat Ameba seems to wear? In Ken's own words again:
Most recent Ameba side view
KH: The concept for the obstacles/wall tactile sensor was determined a long time ago but the implementation seemed a bit of a swine. I needed a circular conductive ring, the center of which needed to be spring (rubber) mounted, above the center of the 'bot. This device is, in effect, the common of a multi-position switch where 0, 1 or 2 contacts of 4 (maybe 8) can be closed at a time. Oh, but the accuracy required....
KH: Ah, what the hell; to make a long story short I found two versions, sitting side by side, ready made. But of course they couldn't be the right dimensions, right? Wrong! One was a 184gm can of turkey flakes while the other a 213gm can of Pacific Pink Salmon :)
A four-point switch, for the time being, with adjustable contacts. Looks pretty good.
Multi-position switch
Ameba with hat
Ameba in her sensor shell, with an Egg in her collector. Makes us think of a mechatronical crab. To be continued...

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