I'm impressed with the Pi4 for embedded computing. I have a Pi4 right here on my desk that is running a robotic motion control application. It does a full kinematic solution for a 12 degree of freedom waking "dog" robot. This involves many 4x4 matrix multiplications and dozens of forward and inverse trig functions per cycle. All this is written in Python. The Pi4 can do about 2100 cycles per second. I was very impressed. At the very most my use case needs 300 per second and I'll likely run the loop at 100 or less per second. This is my "servo control cycle".
I can also run the same code in my Xeon-based workstation. One Xeon core can run the loop at about 4,000 cycles per second. Only twice as fast as the Pi4. (But the Xeon has 16 cores) In other tests the Pi does poorly. It is not good at all at moving data around between the network and disks or disks and memory and it is even worse when it comes to graphics performance. As a machine controller I am very impressed with the Pi4. I am running on battery power so I do care about power use. I suspect that the only thing I will find that outperforms the Pi4 in terms of computing power for its size and weight is a cell phone. All Android phones run Linux under the hood. But interfacing an Android phone to a milling machine is nearly impossible unless you just use it as a kind of remote controller pendant. It looks like it is getting hard to run software step generation on a new PC class computer. It's just as well because now there are very good low-cost microcontrollers. On Fri, Feb 11, 2022 at 3:40 AM gene heskett <ghesk...@shentel.net> wrote: > On Thursday, February 10, 2022 3:05:57 PM EST Chris Albertson wrote: > > Yes, "Mini ITX" is just a shape and a standard for where mounting holes > > go but it is a shape that is sold to a cost-sensitive market where low > > power ususage and low cost maters. The ITX market is large enough > > that mass production drives prices down. So it is a good fit to > > hobby-level machine control. I would think a good place to look as > > Aliexpress as most of this stuff ships from China at very low cost. > > > > If you are never going to use the computer as an interactive desktop > > you could use a Raspberry Pi4. Then use any standard PC notebook to > > remote log-in and run the display from the notebook over WiFi. A Pi4 > > is 1/2 the cost of the cheapest ITX board. > > I did this just to see if I could, but the interfacing from the pi to the > lathe IS the cost of the ITX board over and above the 2 gig rpi4. When I > did it, the 7i90HD was suggested, but while it has numerous ways to > configure 72 i/o's, its fpga has no buffering and the 3 50 in i/o sockets > are a PITA to wire uo to, and leave the fpga wide open to being blown by > noise fron ground loops etc. Enter the 7i42TA, the protection magic for > the 7i90HD, but it takes 3 of them. Now I think it would survive the EMP > of a tactical nuke. And because the i/o is there, and now on green > terminal strips that are much easier to wire, I have all sorts of extra > stuff hooked up and running, like a pair of $20 100ppr dials to replace > the missing cranks, speed selectable on a 1,2,5 etc scale from .0001" to > 20 thou per click, one per powered axis. All the modular outputs were > used from gpio-0 to the end of the config installed, and I used the gpio > from gpio-71 down for such things as controlling ALL the lathe power with > a couple 40 amp AC SSR's which are switched by the state of F2. I could > go on, but if this lathe ever grows a controllable tool changer like the > EMCO-5 or similar I have buckets of i/o currently unused. > > And that rpi4 is running the full desktop raspian buster install. With a > preempt-rt kernel I built on that rpi4. Obviously I shouldn't run FF at > the same time as LCNC as FF plays hell with the latency, but I have > carved air while running FF just to hear it stutter. And it does, but > nothing else seems to bother it that much. > > I'm useing the SPI interface version of the mesa file for the 7i90HD and > the 3 wire interface has been bulletproof. No comm errors. > > At about 25 watts total for the rpi4, interfacing and 11 watt monitor, I > don't even have a power switch to shut it off. With a small $35 ups and a > 20kw generac in the back yard, uptimes are most of a year, till I need to > add something else, I have the i/o left to do it, whatever it might be. > > SPI to/from the pi is faster than any other comm method we have, its in > 32 bit packets at 41megabaud from pi to mesa card, and 25megabaud coming > back from the mesa card to the pi. > > So it wasn't as cheap as I was expecting but the plethora of i/o has had > me considering converting the rest of my machines and saving about 600 > watts by shutting down a bunch of old i5 dells, but thats 600 watts of > non-free heat this time of year. > > > On Thu, Feb 10, 2022 at 5:57 AM andy pugh <bodge...@gmail.com> wrote: > > > On Thu, 10 Feb 2022 at 03:04, andrew beck <andrewbeck0...@gmail.com> > > > > > > wrote: > > > > Its just kinda hard to ship to New Zealand from UK. > > > > Anyone got a oceania source or asia > > > > > > Mini-itx is just a motherboard standard. > > > > > > mini-itx.com just happens to be a UK supplier. I often suggest using > > > their board finder, but then you can hopefully find a local supplier. > > > > > > -- > > > atp > > > "A motorcycle is a bicycle with a pandemonium attachment and is > > > designed for the especial use of mechanical geniuses, daredevils and > > > lunatics." > > > — George Fitch, Atlanta Constitution Newspaper, 1912 > > > > > > > > > _______________________________________________ > > > Emc-users mailing list > > > Emc-users@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > Cheers, Gene Heskett. > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author, 1940) > If we desire respect for the law, we must first make the law respectable. > - Louis D. Brandeis > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
