Automatic synchro drive

Finally getting around to writing up some MOCs...

<http://www.youtube.com/watch?v=0p7OMVMWD3A>

<http://www.brickshelf.com/gallery/aeh/sychro/ldraw/synchro.mpd>

<http://www.brickshelf.com/cgi-bin/gallery.cgi?f=413992>

I wish I could take credit for this remarkable invention, but in fact I got the
idea from <http://www.youtube.com/watch?v=-uTApFE8H90 here>.  Not having any
instructions for this one, I made my own, and tried to make it a bit more
streamlined in the process.  (It's worth looking at this person's other youtube
videos - there are some very interesting things - is it anyone here?)

It moves around, avoiding obstacles in its path, but it does so with only a
single motor and no electronic components.  (Like
<http://news.lugnet.com/technic/?n=15547 this one> and
<http://news.lugnet.com/technic/?n=14957 this one>).  Power is supplied to a
differential, which can drive either the 4 wheels together with the outer
Hailfire ring, or can make the wheels change direction.  Because the latter has
more friction, it goes in a straight line until the ring is prevented from
moving, when it changes direction.

Enjoy! Alexander