I wouldn't normally take the bait, especially from someone who has very little if any practical experience building or running CNC machines, but here goes.

Quote Originally Posted by Jess View Post
And, of course, that ethernet motion controller is a computer.
No it's not. It'll be an embedded micro-controller, DSP or FPGA, which nobody who deals with such things will class as a computer.

On the LinuxCNC side, whilst RS485 is more popular, there's definitely people interfacing their machines to their computers with CANbus.

The hardware's been available for years. There's plug in cards that provide the interfaces plus industrial PC motherboards that already have CANbus and/or RS485 on board.
But not in the form of communication between a computer and a motion controller. In LinuxCNC the computer is the motion controller. External motion control cards are not available for LinuxCNC, as they defeat the whole purpose of LinuxCNC's realtime kernel.
CANbus/RS485 is just another method of communicating between the controller and drives/IO boards, just like lots of other possible options.

Rather unfair and misleading. CANbus gives you something much closer to a PCI I/O board in function - you're not having to do software step generation, and you actually have the ability to read encoders.
And what exactly is a parallel port?
Last I checked, it was simply a bunch of I/O pins conveniently arranged in a standard format, that can be accessed directly by software (I know windows blurs this, but the principle is still there), just like a PCI IO card does.
If you really wanted, you could make a parallel to CANbus to BOB setup, and it would give you a similar setup to using a direct CANbus PCI card, just with more limited IO and speed.

To seque this into the topic of the thread:

Approaches that allow your computer to more directly control the machine is definitely of huge value if you've got some complicated/non-standard kinematics going on, but even on a standard perpendicular axis mill then there's a potentially a significant financial saving to be made.

The additional costs associated with Mach 3; Windows licenses, Mach 3 licenses and ethernet hardware motion controllers could buy you all the electronics you need to convert something like a Novamill or Triac, even once you've thrown in something like a Mesa Anything I/O.

LinuxCNC on BeagleBone Black? A back of the envelope calculation suggests that I can have my entire dedicated control computer as well as software and breakout for the cost of the Mach 3 license alone; that's a lot of difference.
And this argument over cost will rumble on indefinitely.
The fact remains for your typical DIY CNC enthusiast, the familiarity of windows based computer systems, means they'll remain the most popular option for the foreseeable future, despite the additional cost.
You've got to remember, a lot of people who build CNC machines, are not computer or electronic geeks.

For me personally, time is money, so although I may save on licenses, the extra time familiarising myself with a new operating system/hardware, is time that could be spent making money. For me running Dynomotion products, a KFlop costs about £230 delivered. For that I get nearly everything needed for a motion controller including some very reliable software, and only need to add a windows PC, which can be picked up for very little. I can have the controller configured and ready to go in a couple hours. If the computer fails (which lets be honest, is usually the weakest link), I swap the configuration files onto a new computer, and away I go again.

Add something like Mesa cards into the mix, and you've then got to start swapping parts around, and hope they didn't get killed when the computer died.