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From: cs153020@cs.brown.edu (Joel Scotkin)
Newsgroups: sci.virtual-worlds
Subject: Re: rambling on motion
Message-ID: <11014@milton.u.washington.edu>
Date: 12 Nov 90 15:03:46 GMT
References: <10924@milton.u.washington.edu>
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Organization: Brown Computer Science Dept.
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In article <10924@milton.u.washington.edu>, frerichs@ux1.cso.uiuc.edu writes:

|> another way is to use mercury switches.  A small bead on mercury rolls around
|> inside a container with sensors at various angles.  A couple of these togethe
r
|> at strategic angles could detect most rotational and leverage movements, but
|> not lateral (at least I can't see it being able to).
|> cheap, sturdy solution...but slightly limiting.
|> 
|> does anyone else have any comments on any mistakes in logic or tech I have
|> made
|> -or-
|> does anyone have other solutions to the motion sensing problem?


It seems to me that the lateral motion problem is fairly easily solved,
especially if all that is needed is direction of motion, and not speed.
(Obviously speed IS necessary for some things, but maybe not for certain
simple tasks.)

To detect lateral motion all you need is a thin reed between two switches :

                        }       |       {
                        }       |       {
                contact1        |       contact2
                                |
                                wire

when the hand (or whatever) is moved to the left, the wire will tend to
happily stay where it is, and will bump against contact2, either completing
a circuit, or depressing a variable resistor to give an analog current 
corresponding to the acceleration of the hand.

This acceleration can then be processed to determine speed and direction.
You would need three of these sensor pairs, but they should be VERY cheap
to build.

BTW I think that this is how the ear works - with a combination of the
mercury balls (little floating spheres in the inner ear), and the lateral
sensors (the ear uses a liquid which pushes against one pressure point.)


Joel Scotkin
cs153020@cs.brown.edu