Hi Chris,
Let's take the "wrist" joint for example, or any joint for that matter, it doesn't make any difference. It and the stylus is pointing straight down and the length from the pivot point to the tip is 100mm, you press zero at this point, the counter is 0.
Now you rotate that single joint 20° (1200 counts), the tip has moved 34.2mm "away" and 6.03mm "up", you collect that point. Now move it another 20°, this time the same amount of rotation in the joint (20°) moved the tip 30.08mm "away" and 17.36mm up.
Now concider that you from the beginning had pressed zero at the "20° position", the counter is reset to 0. Now you rotate the joint 20° (and ends up the previous 40° position) the counter says 1200 counts which is of course correct but where in 3D-space is the tip?
Is it 34.2mm "away" and 6.03 "up" from your "zero" like before or is it 30.08mm "away" and 17.36 "up"? Obviosuly the later is correct but how would you calculate that when you don't know that your "zero" was actually 20° from dead straight vertical - all you got was 1200 counts.
As far as I can see it will impossible to calculate the position of the stylus without having some kind of absolute reference to start from, like all joints at 90° to each other or something. Therefor my sugestion to use the index-channel. But since you have reduction that may not be as easy as I first thought.
Does that make sense or is it me who's missing something?
/Henrik.
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