[DampRobot]

Originally Posted by Boe

I did a presentation for my team's newer members on this and used this to explain and show gear ratios. http://www.gearsket.ch/

I also sketched up roughly what a drivetrain ends up being inside of it.http://i.imgur.com/frgi7EU.jpg?1

Be sure to note that 99.9% of the time, the ratio between the inter and outer wheels is 1:1. You've got a reduction from your center wheel to your outer wheels in the second image.