[MWB]

Originally Posted by billbo911

Why do you need that much reduction?

Let's see, the Vex motors run at up to approx. 100rpm. The sun revolves around the earth at almost exactly 1rpd. (In fact, it is so close that the error is negligible for this application.)
So, 100rpm * 60 * 24 = 144000rpd

That is way too fast for a "Solar Tracker".

Now based on the photo, Your reduction is: 800.33/1
((84/12)^3)*(84/36))
So now your output shaft is running near 180rpd at full speed.

Using some simple control logic, you now have a very controllable solar tracking system.
May I ask what you are using to sense the position of the sun?

Just something that made me think... Doesnt the Earth revolve around the Sun? I think that you meant to say that the "Earth rotates around its axis at a rate of almost exactly 1 rpd." Not trying to say that you are wrong, just that your wording could throw some people off.