Tandem/Dual Mtr/Y-Axis/Simple Pos-Dir Encoder Fdbk Conversation about grbl

[simen]

Personally I think this is a non-issue. I have been running grbl with dual Y axes for two years with no problems. A dead reckoning stepper driven CNC rig may never ever miss steps or you will find yourself in a world of pain and broken bits anyway. I just use two separate stepper drivers that I connect to the same outputs on the arduino and off I go. If I WERE to implement something like this I would use the incredibly precise and user friendly rotary encoders from austria microsystems:

http://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encoders

But I think you should try running open loop for a while to determin if this is a real problem. If it is, you should probably go for stronger motors, drivers or both before you implement complicated counter measures like this.

As for debugging and quality control I am all for rigging up a cnc with precise rotary encoders, but not for milling.

There has been some talk of introducing a fourth rotary axis, and I'm all for that. Don't hold your breath, though. I will probably not do it myself, but if someone contributes a patch, I intend to lovingly integrate it as a standard part of Grbl.