On Thursday 23 January 2020 13:17:44 Chris Albertson wrote: > The trouble with the Mesa FPGA design is that it depends on a computer > with good real-time performance. It can generate steps but I don't > thing you can run a position or velocity PID control loop on the FPGA. > > You asked about "my controler". No this is not my idea, this is how > most current designs work today. You "push" the real-time control > down stram as close to the physical motor as possible. In the old > days computers where expensive and you wanted to minimize their number > but tocay a 32-bit computer with floating point math, RAM and quita a > lot of > peripheral hardware cost as littel as $1. I buy these $3 PCBs for > controlling up to two servo motors with quadarue feedback > > ebay.com/itm/1pcs-STM32F103C8T6-ARM-STM32-Minimum-System > <https://www.ebay.com/itm/1pcs-STM32F103C8T6-ARM-STM32-Minimum-System- >Development-Board-Module-For-Arduino/183440464510?epid=10003269727&hash >=item2ab5e75a7e:g:klEAAOSwi1pboKF~> > > The above part sells for under $2 and there is a CAD drawing and a > schematic if you scroll down. This will run a couple motors and > encoders and talk over USB all at the same time. For $20 you can get > something 100X more powerful. Or in a larger project use several of > the above. Last order I bought ten of these. > > So how complex is the controller? Very complex. It is an entire > 32-bit computer with FLASH memory and USB running an RTOS. It is not > at all like a 1980's vintage microprocessor. These old chips needed > special programming hardware and were not easy to use. Today we > program FLASH via the built-in USB interface. Yes the thing is > complex but today such a machine costs $1.78 with free shipping and is > very easy to use. You can buy them by the dozen. > > There are four or five development platforms. The Arduino platform > works for simple stuff. You can set up Eclipse and GCC, "mbed" is > easy to use and STM has a very good and professional level system too > that is free. > > As a reference, I have a few quadcopter racing drones. These use four > three-phas brushless motors that must be controled VERY accuratly > using an 8000 Hz PID loop. The main controler PCB is 32mm square and > ha a high-end STM32 microcontroller. There are four high speed serial > interfaces to fur motor drivers and each drive has another STM32 > microcontroller to do motor commutation and feeds back power used to > the man computer. The main computer runs an RTOS and talks to the > two digital radio, IMU and GPS. Fits in a 32mm space and costs maybe > $30. Again VERY complex but they are easy to use. > I looked at that, but fail to groc, lack of docs linkage, and probably some NIH syndrome on my part, how 2 of those would co-ordinate with each other to maintain the gcode paths for a 4 axis movement would be done?
Thats not a schematic, but a logic diagram with black boxes for the active parts. Furinstance, Where does the step/dir's come out to drive the motor power drivers? Too much, too new, for me to comprehend quickly. OTOH, I am getting very very close to a perfectly working rpi4 running this big lathe. So my attention is on that, and building more optimized kernels ATM. Currently zero overruns while running on-demand at 850 kilohertz clocking, reported when stopping LinuxCNC after several hours run-time. And the kernel installed isn't even rpi specific, the next one I built yesterday is striped of other stuff an rpi4 doesn't need. > > On Thu, Jan 23, 2020 at 6:54 AM Les Newell <[email protected]> > > wrote: > > PCs are cheap, easily available and easy to code on. They provide > > huge amounts of processing power for little money and are very well > > suited to GUI applications. However they are not designed for hard > > real time work. LinuxCNC does a good job but even then it tends to > > be a bit touchy if not paired with some form of control hardware to > > take over the really tight timing. Mesa's FPGA cards are a good > > example. I do a fair amount of repair an maintenance on a variety of > > CNC machines. The majority of them go the same route and use a PC > > for the front end and some sort of custom hardware or PLC for motion > > control. > > > > How complicated does your controller have to be? Mesa's FPGA boards > > for example are pretty dumb and need feeding every 1ms, which > > LinuxCNC handles quite easily on most PC hardware. How much do you > > gain by moving more of the motion control to external hardware? > > > > Les > > > > > > > > > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > 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) 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
