On 10/19/2016 12:39 PM, dan...@austin.rr.com wrote: > > http://www.machinekit.io/ > > Anybody familiar with this? Got a friend who wants to put it on a > BeagleBone Black. LinuxCNC run onboard a Cortex A8 directly and > the HDMI monitor, keyboard, mouse etc plug straight into that, not > just acting as a motion controller from a remote PC. > > Notable benefit would seem to be that the IO is very low-latency > without a motion controller card, and the architecture is 100% > consistent, as opposed the latency lottery that is picking a PC and > its MB chipset and seeing how it works. > > BBB does have 2x 46 pin IO headers. I'm not sure if all pins can > be assigned arbitrary HW functions, but it sounds like plenty > anyhow.
The BeagleBone does make a decent machine control platform, mainly due to it's dual 200 MHz PRU cores that can be used for 'bit twiddling" which helps cover the fairly poor (by x86 standards) interrupt latency and jitter. > He asked me about it and all I can do so far is say "hmm". The > Machinekit website is pretty sparse. Machinekit was created mostly to enhance HAL and RTAPI, with one advantage being wider support of real-time options (thus making it possible to run on ARM systems like the BeagleBone, or anywhere else you can get a Xenomai or PREEMPT_RT patched kernel running). This is why Machinekit is sometimes thought of as the "BeagleBone" version of LinuxCNC, but that's not really the case. Other Machinekit HAL additions like ring buffers, triple buffers, instantiable components, and remote components are useful on any system, including x86. While I use many BeagleBones to control various machines exactly the way you describe (using an HDMI monitor and KB/Mouse connected to the BBB), it is not nearly the same user experience as running on an x86 PC. Everything is noticeably slower on the BBB, and graphics performance is particularly horrid (to the point that the 3D preview display is essentially unusable). If you're willing to work with the limitations of a low-end ARM platform like the BeagleBone, they have their place, but for larger machines, I'd recommend x86. NOTE: Most of my BeagleBone driven machines would probably be considered "toys": various 3D printers, an EggBot egg-drawing robot, a pick-and-place machine (WIP). All small desktop-sized machines where having a full x86 PC is somewhat overkill. My one larger machine (a PUMA-style robot arm) has an x86 controller with Mesa hardware cards which I hope to get running with a combination of LinuxCNC (for the recent Joints/Axis update) and Machinekit (for the HAL layer with ring-buffers and remote components). -- Charles Steinkuehler char...@steinkuehler.net
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