Summary

This is an update of this thing - http://www.thingiverse.com/thing:1715175

It's based on this library - http://www.thingiverse.com/thing:3575/#files

Now both gears has the same number of teeth (10 teeth), which result in a lot more powerful diff (larger teeth, harder to break), and a smaller diff at the same time (less teeth, smaller gear size). However, the ratio is now 1:1.

The STL files you have here are designed so that the large gear has 16 mm in diameter. Should you want a larger or a smaller diff, just alter the "SCALE_FACTOR" variable in the OpenScad source code and regenerate.

See a test here - https://www.youtube.com/watch?v=Fl0kDC48Tu8

This design uses 4 bearings (D8 x d5 x 2.5 mm). You can however customize the bearing size (check "BEARING_OUTER_DIAMETER" and "BEARING_WIDTH" variables).

This design uses 4 M2 pins to fix the gears on the axle (the axle is drilled before). You can change that (see "GEAR_FIX_SCREW_DIAMETER").

This design uses 5 mm precision rods. You can change that (see "GEAR_BORE_DIAMETER" variable).

You can generate an open axle (where you can see the gears inside) by calling "axle_top(open_top=1);" and you can generate closed axle (so that no dust gets inside) by calling "axle_top(open_top=0);".