On Fri, 9 Dec 2016, Gene Heskett wrote: > Date: Fri, 9 Dec 2016 12:05:42 -0500 > From: Gene Heskett <[email protected]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: [email protected] > Subject: [Emc-users] Need advice on joint errors > > Greetings all; > > I could use some advice since this raspi-7i90 uses a com protocol, spi, > that is relatively new, and I believe that is where a noise problem > might lie. > > I got it back to running the right rt kernel yesterday, and I am waiting > on another psu & driver for the x axis. But I did get z moving. Nowhere > near optimized though. That's being moved by the motor and psu I took > off the mill because it was too slow. > > But I am being plagued by joint following errors, both axis's, when its > not moving. There is not any connections yet to the x motor pins on the > 7i90. > > This armhf setup has no PID's, so I've yet to locate where this error is > generated. > > My hookup for the spi is currently some of those rip off the next wire > and plug it in, and each is a piss-poor connector, very poor spring > pressure unless I first take a tiny punch and bend the contact tab > inward so it will even stay on the header pin. I've seen some mention of > 80 ohm series damping resistors, but this initial hookup is straight > thru, and a bit shy of 200mm long. At the speed of this interface, it > really should be treated as a transmission line, but its not a very good > one when its all done with loose wires. > > I got some of the 10 pair female connector blocks from digi-key > yesterday, and the gold flashed female pins, and the crimping tool came > in Tuesday, so I think the first thing I'll do today, is cut those junk > connectors of these jumpers, and make it back up using these good > connectors. That will shorten each wire something under an inch. It also > gives me a chance to put some damping resistors in the signal lines, > possibly cutting down on the ringing and the data errors that I'm > convinced is the source of the joint errors being reported when there is > not any motion. > > So my question is, are 100 ohm R's, which I have in bulk, too much? > > The one mention was of 80 ohm chip R's on the OHPark adaptor board I > assume, which puts them right on the r-pi's header, but when the door of > this box is closed, I don't have room for any additional stickup above > the r-pi, but the interface on the 7i90 faces straight out, so putting > them there, on the other, 7i90 end, is quite easily done. > > I'm also aware this is new ground, so what have the explorers here found > is the best solution for an spi driven setup? > > Did you use loose jumpers, or did you use a ribbon cable, arranged to put > a grounded wire between the signal wires? I have around 80 feet of 26 > wire ribbon cable, so thats not a problem. > > The pin pattern on the r-pi is easily covered by one, or a piece of one > of these header blocks I have now. > > Using ribbon cable makes it a lot easier to think of it as a transmission > line, but how best to terminate it for least vswr? > > So lets talk. > > Thanks everybody. > > Cheers, Gene Heskett
The SPI pinout is designed to use flat cable which has interleaved grounds. any flying wire interface is liable to be troublesome There are 2 issues here, 1. Is controlled impedance (the flat cable has ~!30 ohm single ended impedance) and 2. Is ground bounce (you want as many grounds between the 7I90 and the SPI master to avoid ground bounce, 8 are available on the flat cable) Also regards grounding, you need to watch out for ground loops that let high frequency noise currents flow between the 7I90 and the CPU. The most critical signal is the clock from the SPI master. depending on the drive strength it may require a series termination resistor (the 7I90 SPI output are series terminated so need no termination ) > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > Genes Web page <http://geneslinuxbox.net:6309/gene> > > ------------------------------------------------------------------------------ > Developer Access Program for Intel Xeon Phi Processors > Access to Intel Xeon Phi processor-based developer platforms. > With one year of Intel Parallel Studio XE. > Training and support from Colfax. > Order your platform today.http://sdm.link/xeonphi > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ Developer Access Program for Intel Xeon Phi Processors Access to Intel Xeon Phi processor-based developer platforms. With one year of Intel Parallel Studio XE. Training and support from Colfax. Order your platform today.http://sdm.link/xeonphi _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
