When I read the chapter describing custom differential in Sariel's book, trying to follow instructions to build it .
Unfortunately, I only had "two" Knob wheels.
Then I came up with a idea that is there possible to replace Knob wheels with double bevel g20t ?
That means I have to build a different frame for three double bevel g20t which the 5X7 studless frame can not house.
After trial and error of building process , I managed to build a frame that can enclose three double bevel g20t and connected it to a turntable .
This differential is going to take more space than Sariel's when actually put to use.
Here is a short video demonstration of this differential .
A link to BS
http://www.brickshelf.com/gallery/rockmvp/Idea/CustomDifferential/dsc09085.jpg