I saw this http://www.youtube.com/watch?v=FWSYa7b3Vjo ] on youtube and decided to try it. This is the result:
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The robot is still in one piece and more pictures are available upon request.
There are 4 3-wire motors in total in use, 2 for power and 2 for steering.
There was little purpose than to test the concept, but it was fun.
Notes:
Over short distances use only 2 supports for axles or there will be alignment issues.
The bevel gears have difficulty transferring torque unless very very precisely aligned.
Very short chain is difficult to tension properly.
If you built something absurd, show it off at competitions, a lot of people will think it is cool.
Numbers added:
Interesting robot concept, and good notes, related brainstorms here:
1 is a related to "2 points determine a line, and its hard to get 3 points co-linear.’
you might try using Vex shoulder-bolts for alignment, rather than just normal #8 screws.
2 Power = RPM * Torque. Does it help to gear up speed before bevel gears, and gear down afterwards?
3 flexible or variable tension chain tensioning might help.
The minimum number of links to change is 1, which is a higher percentage of chain length on a short chain.
4 Show off Cool factor is an important positive feedback for your work.
I could be wrong about this, but isn’t this an adder-subtractor?
Even if it’s not, showing off cool mechanisms at a competition is always fun 
and can be educational too.
I did not do this, but i will expearament with it.
Very possibly, I had the adder/subtractor written down in a diffident layout. The function is exactly the same.