It looks like the XY calculations are quite easy. Its called forward kinematics and can be seen calculated here https://www.marginallyclever.com/2012/02/drawbot-overview/. Next I have to do interrupts on the encoder rotation to make sure I get every tick. For version 0 I think I'm going to put the encoders on the work surface and weights on the belt like a draw bot for simplicity. Then all I need is power to the drill and z stepper. For v0 the electronics will be kept off the shaper and won't have auto correct .