7i80 and 7i77

Hi Todd, Peter, Andy...

thanks for your comments

I had enough testing with the stepper and since i have another idea /option
I'll postpone -fast - stepping tests for now.

looks It doesnt worth the effort, only for this motor/axis.

The design of this rotary thing, allows for the alternate placing of a servomotor instead of the stepper in the pic.. (yes... i'm an old monkey and that's why i previewed this one )


So, now i can change strategy since It will be far more easy to replace the stepper and drive the device with this servo and directly use the 7i77s servos features.
(my only doubt relates to holding torque to maintain a fixed position though...but will see anyway ....)

I already tested the encoder input ok but my problem is that i don't have an amplifier that can be driven with the +-10V output signals of the 7i77

i looked around in ebay etc and only found Hbridge based amps but with PWM inputs like this
www.ebay.com/itm/400569497467?_trksid=p2...e=STRK%3AMEBIDX%3AIT

but no +-10V input

So can you help me out with that ?
(any link to any product with analog input amp ( or circuit diagram)) i can use will do
(motor is rated 85W)

many thanks in advance

ps: this one
pico-systems.com/servo.html
looks very complicated... big, and probably expensive too...
A local supplier here promised he can build some for about $150...
PWM based I saw were tiny boards for around 15 to 30...
so reasonable prices for me can be somewhere between free of charge to around 80 if that's not a naive dream.
and a supplier that can accept VISA with intl shipping including our beloved Uruguay ...

i'm curious about standard amplifiers for 7i77s to drive small motors.. (did i missed any Mesa product ?)

Ok now I´m getting somewere.
I did this:
7.1. Installing on Debian Wheezy and Debian Jessie (with Preempt-RT kernel)

• Run sudo apt-get update followed by sudo apt-get dist-upgrade to bring the machine up to date with the latest packages.
• Install the Preempt-RT kernel and modules by running: sudo apt-get install linux-image-rt-amd64 or sudo apt-get install linux-image-rt-686-pae.
• Reboot, and make sure you boot into the Preempt-RT kernel. When you log in, verify that uname -v includes PREEMPT and RT.
• Add the LinuxCNC Archive Signing Key to your apt keyring by running sudo apt-key adv --keyserver hkp://keys.gnupg.net --recv-key 8f374fef
• Add a new apt source that looks like this: deb linuxcnc.org/ wheezy base 2.7-uspace or deb linuxcnc.org/ jessie base 2.7-uspace (did not work in terminal but worked in packagemanager)
• Run sudo apt-get update again to fetch the package list from linuxcnc.org.
• Run sudo apt-get install linuxcnc-uspace.
• Machine away!

So now its talking to the board and LinuxCNC start without any errors.

However (of course there is a however)
It get really really bad latency now, I dont know it its the updates on debian I did or something else but before when I first installed the debian hybrid and updated to 2.7 I got about 20000 max but now its crazy , stays at about 16000 if I dont do anything but as soon I move the mouse it can go up to 1000000 (yes thats six zeros)
I have search bios and tried to change almost every setting with only slight improvment

I have also done this:
sudo -i
cat /sys/devices/system/cpu/cpuidle/current_driver
output: intel_idle
nano /etc/default/grub
edit the line GRUB_CMDLINE_LINUX_DEFAULT="-original parameters-" to GRUB_CMDLINE_LINUX_DEFAULT="-original paramters- intel_idle.max_cstate=0 processor.max_cstate=0 idle=poll"
Save and exit
update-grub
reboot

Which improved it somewhat but not anything significantly.

andypugh wrote:

Latency with PREEMPT-RT is never as good as with RTAI, but with an FPGA card you don't need such low latency.

However, even with an FPGA card 1mS latency is too high.

I don't know what the tricks are to reduce PREEMPT-RT latency, they are probably not the same as those needed for RTAI.
However, you can't (as far as I know) use the 7i80 with RTAI, so the issue is moot.

Is anything here helpful?
taste.tuxfamily.org/wiki/index.php?title...or_PREEMPT-RT_kernel

(from a quick skim, it might be that the standard LinuxCNC latency test might not work with PREEMPT-RT)

It may be but in LinuxCNC I soon efter startup get the error "Unexpected realtime delay on task 0 blabla run Latency test and resolve before continuing"
Or could it be the ethernet connection that cause problems?

I tried this now cyclictest -n -p 90 -i 1000 from the link you sent me but I get the error that the command does not exist?

Edit: Get and install of course

Also if I set the servothread to less than 1500000 I get the realtime delay error, I guess a servothread of that magnitude would not give so good performance

Did you
sudo apt-get install rt-tests
?

If you have 1 ms latencies you are not going to be able to run a 1 ms servo thread

The standard linuxcnc latency test works fine with Preempt-RT, as does the latency-histogram

Most of the RTAI latency reduction tricks work with Preempt-RT, so the advice here still applies:

wiki.linuxcnc.org/cgi-bin/wiki.pl?Troubl...ck_dmesg_for_details

What hardware do you have? That might help with determining the cause of the latency

Yes still learning that

Its a real small and cheap mini pc with Intel Celeron 1037U Dual-Core 1.8GHz Processor
I expected it to cause some trouble but not like this, and as I said before it worked much better before.