Saw this design from fablab_ruc_dk Not having any of the Encoders I thought I might play about with some old mice and optical end stops before ordering encoders from China. The holes are all the right size for the Encoders 6mm Shaft 600P/R Incremental Rotary AB phase the extra wheels with the 120 degree holes are extra to mount the laser cut encoders I have not made any mounts yet for the mouse innards or opto endstops as this is part is the experimental hack another thought was to try high grade high precision potentiometers in a potential divider cct then use atod inputs on the arduino.So here is my hacker type re design the encoders are based on a 0.15mm to 0.17mm laser kerf and are at 2 degrees spacing any closer and there would be nothing left. I added an Arduino mounting area so its all kept together on one platform.Original designhttp://fablab.ruc.dk/diy-digitizer/Great links to look at for mouse repurposing:-.https://sourceforge.net/projects/mousesensor/files/. http://thedenneys.org/pub/robot/encoders/http://ferretrobotics.blogspot.co.uk/2011/01/interfacing-optical-mouse-usb-with-pic.htmlhttp://www-bsac.eecs.berkeley.edu/~sbergbre/research/publications/OpticalMouseHack.pdfhttp://diy3dprinting.blogspot.co.uk/2015/05/diy-contact-3d-scanner-with-arduino-and.htmlhttp://www.wildcircuits.com/2013/03/optical-mouse-hacking.html?view=flipcard