RS-485 connectivity to cheap chinese AC Servo

[aparfeno]

Hello,
Hello, i need help debugging poor connectivity between PC and an AC Servo driver.
I've bought a 750w AC servo + driver off Amazon ($299) for un upgrade to my CNC Index Wells knee mill (https://www.amazon.com/dp/B09B75P9Y6/ref=cm_sw_r_apan_glt_i_3KGD6DW341GSMAXPE5PJ?_encod ing=UTF8&psc=1).

The motor and driver seem to be pretty well built, but come with chinglish documentation, two RS-485 ports and NO cable to connect it to PC or other RS-485 host. There is software that should work and help tune the drive once I get the driver connected to the PC successfully. This is where I need help.

According to the manual, the software uses Modbus over RS485 to interact with the driver, so:
1) I got an USB-485 adaptor with FTDI chip
2) I connect rx+, rx-, ground from the adaptor to the driver's RS485 connector
3) Vendor's own software connected successfully! Also a 3rd party software "modbus poll" also connected successfully
4) i activated the drive (so it became energized) and I started to get CRC errors/checksum

So it is apparent that energizing the driver creates some interference in RS485 line. I am a complete noobie in this stuff, so I would really appreciate any help.

A little more about my setup:
1) The RS485 port on the driver is RJ12 jack. To connect, i took 4" of flat phone cable that happened to use the same pins and connected the other end to the USb-485 adaptor so that rx+, rx-, and ground are connected.
2) the motor itself is moved far from the driver
3) I tried adding a 120ohm resistor, but resulted 100% communication failures
4) I tried not connecting the ground, and that also resulted in 100% communication failures

So, i would like to understand: is it a cable or the driver itself can't really do RS485? Maybe i should get a shielded cable ?

Thanks all for any help!

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[Jim Dawson]

Is the drive properly grounded? I guess I would start with a shielded cable. You may also need a line filter on the drive power input. https://www.amazon.com/powerline-fil...erline+filters