Wiring a Chinese servo to a 7i77. Setup for yet another newbie

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14 Oct 2019 22:46 #147897 by SPH
Hi again. I've got a bit of a build thread started in the cnc machines section but I have a few questions about setting up my 7i77 so I figured I'd ask in here.

I've only ever dealt with stepper systems and mach3 so this is all a big step.

Ive got my servo drive connected and setup (super basically at this point, no tuning yet) and can supply it +-10v and get rotation. There's a 60 rpm or thereabouts drift at the moment but i wont worry about that untill ive got the drive enable handled by linuxcnc and the loop closed.

I'm a bit lost on the mesa pins for the encoder vs the servo drive encoder outputs. The 7i77 lists, as cut straight from the manual:

TB3 PIN FUNCTION DIR

1 QA0 TO 7I77
2 /QA0 TO 7I77
3 GND FROM 7I77
4 QB0 TO 7I77
5 /QB0 TO 7I77
6 +5V FROM 7I77
7 IDX0 TO 7I77
8 /IDX0 TO 7I77

and so on for each encoder. My servo drive speed/torque wiring details an A,B and Z +- signal wire and a 'Z collector open circuit output' and ground.

You can see the wiring diagram listed on page 24, link here.

I need a bit of help getting everything wired correctly. I've read a bunch of build and setup posts and there's enough references to burnt boards to make me cautious. Probably more an issue for the field and signalling wiring but I'd still rather go at it armed with half an idea.

Any help greatly appreciated.

Cheers

Sam

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14 Oct 2019 22:51 #147899 by SPH
Oh, and if anyone's got suggestions (or an existing example more like) of wiring the enable and reset etc I'd love to see it. I can work it out and post my plan for some feedback but if someone's got the wiring handy, you know, shoulders of giants and all that ;)

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14 Oct 2019 23:03 #147902 by tommylight

SPH wrote: TB3 PIN FUNCTION DIR

1 QA0 TO 7I77 PA+ pin 20
2 /QA0 TO 7I77 PA- pin19
3 GND FROM 7I77 GND pin 1
4 QB0 TO 7I77 PB+ pin 18
5 /QB0 TO 7I77 PB- pin 17
6 +5V FROM 7I77 do not connect
7 IDX0 TO 7I77 do not connect
8 /IDX0 TO 7I77 do not connect

Also +-10V from Mesa to pin 25 and 13 respectively .
Drive enable from Mesa to pin 29 and 9.
The following user(s) said Thank You: SPH

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15 Oct 2019 02:27 - 15 Oct 2019 02:29 #147909 by SPH
Ahh, ok, so the third phase of the encoder isn't used?

Or I guess more to the point I obviously don't quite get the A,B,Z encoder outputs. I'll read up a bit.

Regardless, I should now be able to get the drive wired to the 7i77 and start trying to get things moving on the bench.

Thanks again!
Last edit: 15 Oct 2019 02:29 by SPH.

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15 Oct 2019 02:58 #147910 by Todd Zuercher
The Z phase of the encoder is an index mark. It is optional, and often used to make homing more precise.
The following user(s) said Thank You: SPH

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15 Oct 2019 04:10 #147914 by SPH
So if I connect the encoder plug to the 7i77 I get some signs of life in the axis test page when I turn the motor shaft but if I connect the TB5 drive plug with the +-10v connectors the 7i77 powers off. Comes back on if I disconnect the plug. It's a bit nerve wracking to be honest.

I've got TB5 pin 4 (AOUT0) going to pin 25 (VREF +) on the drive and TB5 pin 3 (GND) going to pin 13 (AGND) on the drive as suggested.

The drive isn't (wasn't) enabled when I connected the plug.

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15 Oct 2019 04:48 #147915 by SPH
I said 'powers off' but I don't actually know what it's doing. Before I plugged the TB5 connector in I had the top left orange led and the middle two orange led's lit. They go out when the plug is connected.

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15 Oct 2019 05:46 - 15 Oct 2019 06:02 #147917 by SPH
With little else to try switched the +-10 wires and replugged them. The board doesn't shut down now.
When the drive plug is connected I read 4.8v between pins 3 and 4 on the TB5 connector and if I enable the drive it runs at something like 750rpm. As you'd expect, i guess, for an output of 4.8v. If I disconnect the TB5 plug the pins go back to 0v.

Anyone have any insight on those drive pins? I don't know if I've actually found the issue or just a way to make it not crash. As it is now I've got pin 25 from the drive going to TB5 pin 3 and 13 to TB5 pin 4.
Last edit: 15 Oct 2019 06:02 by SPH.

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15 Oct 2019 06:25 - 15 Oct 2019 09:43 #147918 by SPH
God, I'm an idiot and am lucky I didn't cook something. I'd read so many posts about people wiring things backwards and had even said to myself "I wont be that guy", well, I'm that guy too. I had the encoder plug wired back to front. 1 as 8 etc. So I was getting small signs of life in the HAL config page but my DRO wasn't counting. What I thought was pin 3 on the 7i77 TB5 was actually pin 6 and therefor was sending 5v to the ground on the servo drive and then getting back fed to the +-10 circuit.

Lucky the board seems to have been able to handle it.

Now that the wiring is around the right way with no wayward voltages everything is working nicely!
I have a motor that's actually tuned half ok! I've only had to change one parameter in the drive and that was to put it into speed control which is quite a surprise, don't know if it's a fluke or what but all I've had to do is connect it and tune via the calibration screen. Just a bare motor mind you, it might be a different story once everythings connected up.

One thing that's struck me with the HAL scope and watching the DRO now the first servo is connected is just how damn instant everything is. I'd always hated how mach3 felt like you were driving it with a pole, always seeing things after they happened.
It's awesome being able to put my hand on the motor shaft and see the few tiny vibrations I've still got reflected in the DRO.

Still a long way to go, I'll likely have a lot of things to change once I get the motors in place and can actually tell which way they should be turning and put some load on them but all in all a far better end to the day than it was looking like a few hours ago.

Oh! I'm still not confident I know how to hook up the drive enable. If someone could spell it out for me I'd really appreciate it. For someone who considders CNC a favourite hobby, basic electronics still catch me out often enough.

Pretty sure I need to send +24v to pin 9 on the drive and - to pin 6? The answer will seem really obvious in the morning no doubt.

Thanks again all.
Last edit: 15 Oct 2019 09:43 by SPH.

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15 Oct 2019 11:04 #147922 by tommylight
You do not need to send anything, one of hose pins is the output signal power supply, the other is the input that enables the drives.
Take a multimeter set it to OHM ( usually 200 ) or to test for shorts with a buzzer if it is an auto DVM, connect the probes to those two pins and check if it enables the drive. Check the polarity of the probes when it enables and wire them to Mesa accordingly.

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