After some searching I couldn’t find anyone that had attached the new mico gear motor encoders to the 3pi platform. At the black friday sale I picked up a little bit of everything and spent an hour putting it together this morning. It is an intermediate soldering job to do the following. The good news is that everything fits.
Remove the stock 30x1 3pi motors. (Unscrew the plastic motor cover, and then desolder the two motor pins from the 0.1 inch pins.
Replace them with the 30x1 dual shaft motors. https://www.pololu.com/category/141/micro-metal-gearmotors-with-extended-motor-shafts
Insert the encoder electronics module. https://www.pololu.com/product/2590
Solder at least 4 wires to the module. I used wires terminated in standard 0.1 inch pins, but you can also use 2mm cable as the pin spacing is 2mm instead of 2.54 mm. This is a bit fiddly after two cups of coffee. (Hey pololu, dump the M1 and M2 and give us a 2.54 connector for fat american hands. ( I really wanted to solder a 2.54 mm male header here. Yes I have 2mm headers from working on so many korean projects, but who else does!)
Hook up power and ground and check the output on a scope.
It is going to be a bit tricky as it would be nice to have one interrupt per encoder, but I will steal IO off the LCD to make this work, the other interrupt is tied to one of the motor control pins. I will probably end up using the pin change interrupts.