Just Getting Started Have Servos Need Direction

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27 May 2019 03:39 #135038 by JuniorC
I've been doing a little ready over some instructions on both the Parker Gemini GV drives that I have and the 7I77/7I77D. I'm not sure sure which Superport FPGA anything I/O card. Because I haven't gotten a computer yet so the type of slot is unknown.

Hakan. Was asking about the drive being digital. From what I'm reading is that the digital I/O are optional. Also the drive can be configured as a +/-10V command or a pulse inputs which all seem to be analog. Not sure which would be the best configuration? Like I said I'm new to this and I'm always up for a challenge. I've looked for a digital interface but I can find one. It looks as if the Mesa 7I77 or 7177D plug-n-play would be the way I need to go. But I'm not sure which one the 7I77 or the 7I77D?

As far as configuring the drives I'm going to download the software and see how they are currently configured. And then try to configure them myself if needed. An electrical engineer I work with said he help with the drives if needed. Now far as configuration of the Mesa card and LinuxCNC there will probably be questions to come.

I have attached a file that contains the drive I/O connector which shows the required I/O and a little more info on the digital side of the drive.

Thanks again for everyone's input.
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27 May 2019 18:36 #135080 by bevins
7i77 would work. The D version is for sinking. Dont really need it.
Encoder out is there, step & Dir is there along with velocity mode +_10v.

Your set man.... Get an ethernet board like 7i92M and wont have to worry about which pc slot is there.

Just my 2 cents

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27 May 2019 19:03 #135081 by Hakan
I considered the step/direction which is included in the driver as far as I can see. I have recentyl tried a servo with pulse/direction using my standard stepper rmotor setup and saw no problems with that, instead it performed great. But I am by no means an authority on this so if the servo people say +-10V then go for that.

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27 May 2019 20:39 #135090 by bevins
I would rather have control of what the axis does with LinuxCNC making decisions in terms of errors and what not instead of the drive and have no say. If you go step/dir route, yes it would be easier and probably faster to implement but you are relying on someone 10-15 years ago that wrote the firmware of that drive to decide if the servo is where it is suppose to be. Me personally would rather use +-10v and bringing the encoders back to linuxcnc, then you have control and say on when you want to throw an error. I have more trust in linuxcnc that has been updated last night than some firmware on the drive that who knows when it was updated or written. I have done many machine with both types and hands down I prefer closing the loop with Linuxcnc.

Just my 2.343 cents.

Bob
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27 May 2019 20:59 #135092 by Hakan
But that can still be done with a step/direction interface. I mean that the step/direction is equivalent to the +-10V analog signal. +-10V usually is the wanted velocity or torque, while step/direction is the position, step rate is the velocity. Both signal can be differentiated and integrated to give the same values. For analog drives and servos the +-10V is superior, but for digital drives, well I don't know. With my limited experience both interfaces work equally well there.

The encoder signal can be brought into linuxcnc for closing the position loop in both cases. For what I can understand, the only difference is the interface, all the rest is the same in the driver and not dependent on the interface.

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27 May 2019 21:11 #135094 by bevins

Hakan wrote: But that can still be done with a step/direction interface. I mean that the step/direction is equivalent to the +-10V analog signal. +-10V usually is the wanted velocity or torque, while step/direction is the position, step rate is the velocity. Both signal can be differentiated and integrated to give the same values. For analog drives and servos the +-10V is superior, but for digital drives, well I don't know. With my limited experience both interfaces work equally well there.

The encoder signal can be brought into linuxcnc for closing the position loop in both cases. For what I can understand, the only difference is the interface, all the rest is the same in the driver and not dependent on the interface.


Yes both ways can be done. Not likely with someone just starting out. I have tried it an could not get it to work right. Either way, to me you still have more control with +-10v. The servo drives I use I bypass the drives capability to have input, which gives linuxcnc full control and a true loop being closed by Linuxcnc. I have seen drives where you cant do that and the two fight each other. I am just saying for me velocity control is working the best for me.

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28 May 2019 00:14 #135100 by tommylight
To make it simple,
Get a used PC with parallel port, wire it and start using the drives motors, even if they are on a dinner table.
Later, get a 7i92M and a 7i77, make some more wiring and be amazed at how nice and how fast and how smooth that works, and most importantly how reliable that system is.
As for the analog +-10V/step-dir/cw-ccw, I agree fully with Bevins and his 2.343 cents.

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28 May 2019 01:49 #135107 by JuniorC
Thanks again for everyone's input. I have a cheap breakout board and a old desktop with a parallel port. I'll hook up a few the drives using the step and dir outputs. But first I need to get into the drive and see how it's configured. A friend of mine has an old laptop that has xp pro and a serial port which I need to configure the drives with. I totally agree with you Bevins on letting LinuxCNC be in control. As far as the encoder feed back the drive looks to have A B and Z the Mesa 7i77 card has A B and X. I'm assuming I'm looking at the right thing. Also you talked about having control and say on when you want to throw an error. I'm assuming the errors you're referring to are over travel limits?
Also is the set up of the Ethernet card pretty much the same as a parallel port as far as LinuxCNC goes?
I have an old EMachine that I believe has a bad hard drive. I'll change out the drive and see if I can get LinuxCNC installed. And we'll see what happens.

Thanks again,
JuniorC

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28 May 2019 17:29 - 28 May 2019 17:32 #135184 by bevins

JuniorC wrote: Thanks again for everyone's input. I have a cheap breakout board and a old desktop with a parallel port. I'll hook up a few the drives using the step and dir outputs. But first I need to get into the drive and see how it's configured. A friend of mine has an old laptop that has xp pro and a serial port which I need to configure the drives with. I totally agree with you Bevins on letting LinuxCNC be in control. As far as the encoder feed back the drive looks to have A B and Z the Mesa 7i77 card has A B and X. I'm assuming I'm looking at the right thing. Also you talked about having control and say on when you want to throw an error. I'm assuming the errors you're referring to are over travel limits?
Also is the set up of the Ethernet card pretty much the same as a parallel port as far as LinuxCNC goes?
I have an old EMachine that I believe has a bad hard drive. I'll change out the drive and see if I can get LinuxCNC installed. And we'll see what happens.

Thanks again,
JuniorC


Yes A B Z(index), same as A B X(index). Actually A /A, B /B, Z /Z

Not over travel limits.
When Linuxcnc sends a command to go to XXX, the machine moves to XXX. The encoders tell LinuxCNC where it physically went. IF it is off by a set parameter (in configs), it will throw an error. If it overshoots/undershoots Linuxcnc will send it back and constantly adjusting where it is suppose to be in ref from the input of the encoders.

Open loop to linuxcnc usually the encoders are terminated and the loop is closed at the driver, so Linuxcnc never gets the actual position of the motor/axis. The drive gets the position of the motor/axis and attempts to adjust it to a parameter in the drive. Sometimes adjustable sometimes not depending on the drive.
Last edit: 28 May 2019 17:32 by bevins.
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22 Jul 2019 19:51 #140231 by JuniorC
I'm back with a few more questions. I have a laptop and a desktop that's just sitting around. Both have amd processors. Laptop has an A6 quad core and I think the desktop has an Athlon 64 or 64 FX not sure which. Is there preference between the AMD or the Intel processor. A friend of mine has a few desktops which he believes have Intel inside. Just wondering which is the best choice.

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