Timing Belt Y MXL, Printrbot Simple V2

This is for the Simple V2 WITH String tension ordered AFTER 10/23/2013.
For models w/o string tension see http://www.thingiverse.com/thing:180146
The motor mount and tie bar are identical on both MXL designs.

Having difficulty keeping consistent traction with the string drive on my Simple Y axis, I set out to design a more positive drive.
Design parameters were:

• Timing belt drive
• "Bolt on" solution, no modification of machine required
• Ability to revert back to string drive if necessary

As always comments, concerns, and suggestions for improvements are not only welcome but encouraged.