Gerber 408 retrofit

@fdarling, sent you an email.

Deleted - was not relevant.

MKMII wrote:

So, if I understand correctly, the step on time, step space, direction hold, direction space should be doubled as a starting point?

I found this info online and believe that it may be accurate:
for the X, and Y axis which should allow me to calculate my scaling.
servo encoder counts per revolution: 4000
Servo teeth: 28
Lead screw teeth: 70
Pitch: 20mm
counts per mm: 500

Can you please confirm the "servo encoder counts per revolution"? The RM21D datasheet implies the optional count ranges from 5 to 2,048. While it has a 2,000 option it's not obvious if this is per channel or overall encoder count?

If your interested, I have done a complete 408 retrofit and I keep my configs on github.    

github.com/SkyMoCo/LinuxCNCConfigs

There are some other configs there for steppers on other machines, the XY axis are the same, but the Z is different.  

Here is the progress with the retrofit motherboard, I am just a couple "work days" away from sending the design off for fabrication.

I can hardly wait to see it working. 

I received the prototype batch of PCBs, and have begun testing (photo attached). I have verified that the following is working:

• ±10V analog outputs to servo drives
• encoder inputs
• servo drive related outputs: enable & alarm reset
• servo drive related inputs: drive ready & alarm
• limit/home switch inputs
• spindle enable relay
• "vacuum" & "router" outputs (drive relays in the electrical cabinet that control 120VAC outlets)
• expansion spindle probe and tool probe inputs (24V/5V selectable power, PNP/NPN selectable trigger)
• SmartSerial expansion (6 channels, up to 8 if not using Mesa PacketUARTs)

What remains to be tested:

• the isolated USB areas
• the isolated RS-232/RS-485 areas (driven either from USB or from Mesa card PacketUARTs)
• step/direction outputs on axis expansion headers
• E-stop connector
• bolting the motherboard into the cabinet (verifying mounting hole matches)

I will keep you guys posted! If all goes well, I will be ready to start shipping these units very soon. If you are interested and haven't already contacted me, please email me at my forum username at gmail dot com.

I have completed testing the Gerber Sabre LinuxCNC retrofit motherboard, and everything works! I attached a photo of the motherboard installed in the electrical cabinet, as well as a photo of the original motherboard for reference. There is also a screenshot of LinuxCNC.

My retrofit kit includes:

• retrofit motherboard PCB with Mesa 7i80HDT preinstalled
• 8x M3 mounting screws (in case the original motherboard/screws were missing)
• HP small form factor PC with LinuxCNC preinstalled, featuring built-in WiFi
• optionally: 1920x1080 IPS LCD monitor w/ wide viewing angle, and wireless keyboard/mouse

If interested in purchasing a kit, please email me at my forum username at gmail dot com. I currently have 4 available, though I can have more fabricated with some lead time (I am guessing 2-3 weeks).

Hi Forest! Thank you for dropping me an email, making me aware of the awesome job you did by creating this drop-in replacement board. I am sure it will save a lot of time and troubles for those who want to retrofit a Gerber Sabre machine. Would your board have been available a few years earlier, then I would certainly have ordered it. But I sold my machine two years ago, as I moved abroad..... I am currently working on a new machine, using an Orange Pi 5 with a Mesa ethernet card.

To those who may be interested how I retrofitted my Gerber Sabre 408 machine a few years ago, here is a brief overview:

• I first labeled all wires connected to the old Gerber motherboard 
• then removed the original Gerber motherboard
• kept the servo drives and their IDC-16 cables
• kept the HUGE transformer / power supply for the servo drives
• removed the smaller power supply that powered the original Gerber mobo
• removed the two big relays for vacuum and auxiliary output, and replaced them with solid state relays (SSR) 
• installed a Gigabyte GA-J1900N-D3V mini-ITX motherboard and a small ATX power supply; this board has an old fashioned PCI slot for the MESA 5i23 card and gave me very good latency results (with isolcpus=1,3).
• used the serial port of this mini-ITX board to connect to the spindle VFD via RS232 (MODBUS protocol)
• installed a MESA 5i23 Anything I/O PCI card, with the following daughter boards:
  • 7i48 6 channel analog servo interface; to this I added three 16-pin IDC to screw terminal adapter boards, for connecting the analog servo outputs to the servo drives using their original cables; I also added three 10-pin IDC to screw terminal adapter boards for the encoder inputs
  • 7I37 8 output, 16 input isolated I/O card with a 50-pin IDC to screw terminal connector board, for connecting various incoming and outgoing signals (e.g. limit switches, E-stops, SSRs)
• For the GUI I started with a simple AXIS interface, but eventually switched to qtdragon_hd (with some customizations) as it worked much better with my 27 inch touchscreen.

All in all it took me about a week to figure out how the old Gerber system worked and how to replace the old system with the setup described above, although the real work to get the machine up and running took me longer than I anticipated. While tuning the servo motors, I encountered vibration at higher travel speeds, and despite all my attempts I could not eliminate those vibrations. Then I somehow found Forest, who shared with me valuable information about his Gerber Sabre 408 retrofit, and although his PID setting certainly helped me to reduce the vibrations, they were still not gone. Eventually the cause of the vibrations was not the tuning of the servos..... it was caused by wear of the "ballscrews". The Gerber Sabre machines use teflon coated screws with some hard plastic nuts (spring loaded to reduce backlash). That works great, but as I found out those teflon coatings will eventually wear out. Forest provided me with details on where to order new screws and nuts, but for the moment I decided to accept the optimized settings as they were, as during milling there was no vibration, and reduced the maximum travel speed to avoid any resonance. Forest, again many thanks for all your help in getting me on the right track!
In summary: the way I retrofitted my machine worked very well for me, but if I had to do it again, I would definitely order a drop-in board. Awesome job Forest!!!!!

- Eric -