7i80 and 7i77

Ordering 7i76/7i77/whatever breakout board might be useful, but I do have working electronics on a (home brew) PCB that accepts a DB25. I might want to continue that route since I already use home-brew stepper drives around dsPIC33F DSP's and I do want to continue on the stepper-with-linear-scale-feedback path. My earlier experiments on the BF20 were quite promising, but that machine has too much mechanical backlash. The sound of a hunting 'servo' certainly makes you feel nervous.

I have this idea to run the steppers in velocity mode using FOC / vector drive as 'regular' high torque/low RPM motors. Voltage mode drive would make it easy to detect (and act upon) stall, would not suffer from the 90-degree phase shift a current-mode drive encounters when it runs out of bus voltage, and it doesn't produce the typical 'stepper noise'. And because a stepper with stall detect is fully synchronous I do not need a rotary encoder on the shaft and it makes life for the servo loop very easy since actual RPM is extremely close to commanded RPM. Final position feedback through 1 micron linear glass scales. Sounds like a great setup for machines that do not need more than ~200W of mechanical power to drive the screws. Stepper motor+drive+scale costs less than a single servo motor+drive.

a gantry style machine needs at least 4 axes worth of linear encoders, and possibly shaft encoders which totals to 8. Initially 4 step/dir interfaces are needed; and later on PDM (or a SPI protocol) to the drives to command velocity might be more suitable.

Whether a card supports the amount of encoderrs/stepgens or not depends on the firmware. In this[.url] document there is not much information about the 5i25/6i25.

retrofit-plus.at in Austria sells the 7i80 card. But I asked him and he says, the card don't works correctly. Maybe he only have'nt the newest Software and drivers.

It doesn't work out of the box.

andypugh had to use a kernel provided my Michael Haberler, fetch the development source tree, and build it. This is within my capabilities, and if it fails I am pretty sure the people here can help me out quickly. But it might not be for everyone and development releases are, well, development releases.

Once it work, I don't expect latency problems. Not sure how the LinuxCNC->7i80 interface exactly works, but there are not too many ways to do this. I don't know how large the packets sent over the link are, but you can send and receive at least around 4000 UDP packets a second over a point-to-point 100Mbit link. More than enough to support normal servo thread update rates. Latency would be larger than with PCI/PCIe or EPP since the UDP packet must be received completely and travel through some kind of lightweight IP stack before it can be processed. But compared to the bandwidth of the mechanical system itself it is still 'almost zero latency'.

But Andy is right; the 5i25/6i25 is a safer choice for now and it can do perfectly what I want using the 7i76+7i77 firmware (and 7i76 board to get the I/O). 7i77 uses a multiplexed scheme for the encoders, but it seems to be a simple 2:1 multiplexing scheme with a single selection bit. At least Mesa provides the VHDL sources so it is possible to figure out what they do exactly.

retrofit-plus.at doesn't sell the 6i25 either, or at least not on their site. duzi.cz didn't either. I wonder why? Today i can go to the local store and get a mainboard with PCI support. But this will soon be over, at least for consumer mainboards and gems like the Atom mainboards. PCI support nowadays is already provided by a bridge, and not native. Using PCIe makes more sense IMHO.

[edit]
Andy was faster..
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First posting! So, I am in the beginning stages of my first retrofit of my bed milling machine finally. I am pretty convinced that I want to go the LinuxCNC approach vs Mach for multiple reasons

So from what I gather the Mesa 7i80DB + 7i77 = 7i77E? and the same code and configuration for the 7i80DB +7i77 would work for the 7i77E? My thoughts here are that I could use a microITX (Biostar A68I-350 DELUXE R2.0?) and the 7i77E in the pendant of the mill and run cabling to the drivers in a different cabinet and keep chances for noise level down.

I don't have any problem with the Linux building that Andy outlined to get it running as well as I won't be ready for full blown milling till late spring/summer most likely, so I think that would be enough time to work out any issues. Andy, do you know of any latency issues that have come up? I only ask as there's not much information as of yet and I realize this is a bit on the bleeding edge.

Its a long time ago, since I asked about the 7i80. Now I have received the board and have time to try the part.
In the first page#41426 andypugh wrote that I must type in . ./scripts/rip-environment, but unfortunately Linux answerd
File or folder not found, what can I do to get the file from whereever.

I have now tried some days to run linuxcnc, but unfortunately without any success. I get always errorcodes like can't find loadrt and similiar. If I follow the description on the first page #41426 It runs without any problem but after I try to get the name of the rt system, I get the same, as before the installation. Its a rt System as well, but an older one, 2.6.32 122 rtai iirc. The change of the directory is a bit different, I must add a / before, but then I'm in the correct directory. But the problems occured, from the point "cd linuxcnc-dev
git branch --track ubc3-7i80 origin/ubc3-7i80" After that I get one errormessage after another.
But, if I try to run it don't work. If I run halcmd before I run hm2_eth
it can load it, but nothing happens from that point on.

Sorry, I'm a complete linux Greenhorn, I don't know, what I have to do, that I can run the program.
The Linuxcnc program runs, but I can't communicate with the Mesa boards.