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> From: Steve Hardy <hardy@SWENG.STORTEK.COM>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: Encoder resolution?
> Date: Tuesday, March 04, 1997 2:08 PM
>
> > From: "Jeff 'n Kristen Kroll" <jkkroll@JOSHUANET.COM>
>>the project I am working on, a six degree of freedom
> > trackball
> BTW, just in case you are under a misapprehension, one degree of
> freedom counts both the forward and reverse directions as the
> one DOF.  If you truly have a 6-DOF trackball, my mind is boggling
> trying to imagine how one would drive such a beast, since you would
> need X, Y and Z translation, plus pitch, roll and yaw! -- and 6
> encoders, not 3.
>
> Strap yourself in for a slight digression: did you know that you can
> yaw (spin) a trackball using just pitch and roll?  To demonstrate
> this, take a ball and sit it on a table.  Put your hand on the top of
> the ball.  You can pitch the ball by moving your hand back and forth,
> and you can roll it using side to side motion.  Now if you move your
> hand in small circles, the ball yaws in the opposite direction to your
> hand motion (albeit with some nutation).  Mathematicians will tell you
> that this is a result of group theory, but I think it just works anyway
> in spite of that lot...
>
> Regards,
> SJH
> Canberra, Australia

        Actually what I am working on is a 6DOF trackball. A coupla' months ago
I
moved next door to an inventor who has the patent on the whole arena of
6DOF trackballs( see http://gadgetland.com/globaldevices/trackball.html).
The guy is a mechanical genius and has a prototype that spins in all 3
directions and can translate in the other three. Fortunately for me he
didn't know alot about electronics and is supplying me with all of the
equipment I need (PICStart Plus, PC, chips, PC board design software, etc.)
in exchange for doing this project for him.
        The three rotational axes will be done with encoders and the translation
al
axes will have proportional control, but have a much better "feel" than
controllers currently on the market. This thing will ROCK the game
controller world!
        I didn't quite understand how you can get the yaw from just pitch and
roll. Does this mean I can do away with one of my encoders? If it does,
will I need to do intense computations? I would greatly appreciate any help
in finding out more about this (references, etc.).

                                                Thanx,
                                                Jeff Kroll