Hello,

I'm building a machine in my garage that initially was supposed to be a 
plasma table, no leaning towards a router but what is important right now 
is I have the X and Y axes mostly assembled and wired.  The Y axis is 
driven by a pair of ballscrews with NEMA 34 steppers, driven by DQ860MA 
(fairly cheap) drivers.  I've got this axis wired up to an Arduino mega 
2560 running GRBL.  I just finished attaching a (modified) part of a redbox 
(dvd rental) machine that has a ballscrew, rail w/ carriage, 24V servo with 
controller board nicely packaged so that I could just bolt it to my 
gantry.  

I think I am going to be using Machinekit on a beaglebone black to control 
this thing going forward.  I have no experience with machinekit/linuxCNC 
but am familiar with microcontrollers and 3d printer controls which is the 
reason I defaulted to an arduino for control when I started this project.

My question pertains to controlling the servo on the X axis.  The 
controller board uses a PIC-SERVO-SC (http://www.jrkerr.com/boards.html) - 
the board seems to be a custom version made for redbox.  I have been able 
to power up the board and connect via RS422 and control it using the test 
software provided by the maker of the PIC-SERVO-SC.

The controller offers several control modes.  My instinct was to use 
step/direction input mode, mostly because I understand it. I'd wire step 
and direction from the arduino/beaglebone to the servo controller and 
essentially be done with it.  The servo controller would still utilize the 
encoder for accurate positioning, transparent to the machine controller.  
This is probably simplest, as everything would look like a stepper to the 
machine controller.

I'm wondering if it would be advantageous to utilize one of the other 
control modes instead - I'm especially interested in controlling it by 
serial commands.  I've got a few of these servos and at least 2 functional 
control boards.  I could connect them via an RS485 bus which would reduce 
the amount of cabling I need to run from the controller to the gantry.

How tough would it be to control servos this way using machinekit?  I'm 
very comfortable writing code to control serial equipment, but have no 
knowledge of the machinekit architecture so I wanted to check here before 
spending time on it.

In summary, I'd like to control at least one axis via serial commands while 
using steppers for another and am wondering how feasible that is.  I'm 
hoping to get my wiring done this weekend and need to decide if I wire up 
an RS485 bus or if I should just stick to the familiar stepper wiring.

Thank you

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