Linuxcnc with Teknic SST-1500-UCX

14 Sep 2020 05:26 #182052 by spacemanspiffee
I picked up a used CNT Motion 900 series 3 axis router which currently runs on WinCNC. I'm not a big fan of this controller (not finding it very intuitive, and I'm having some issues with lost motion that I have read some other people had with this controller as well).

I built a small desktop mill with steppers and a Gecko g540 years ago and I run that off LinuxCNC and would like to do the same for my new big toy.

The router has three Teknic SST-1500-UCX for motion. It looks like Todd Zuercher has a setup with some similar drives running using a Mesa 7i77 and 5i25.

I'm basically looking for input on whether this would be a good match for my machine, and general wiring diagrams and setup and whatnot. I'm just getting started on figuring out what it will take to convert this machine so any and all help is appreciated. I'll be doing a lot of reading and may answer my own questions but figured it wouldn't hurt to ask.


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15 Sep 2020 17:39 #182249 by Todd Zuercher
The machine of mine you are referencing is actually a machine that was built by CNT Motion. We have two of their machines, both were custom builds. The one that I converted to Linuxcnc is based off their 900 platform. (The other is 1000 based and is still running Wincnc.) Our 900 based machine never ran Wincnc, it originally was running Microsystems of Buckhannon's old DOS cnc control software (the predecessor of Wincnc). After a lighting strike took out the original DOS PC, we were unable to get the old DOS program to work on new pc's because of security dongle issues. We balked at the cost of upgrading to Wincnc. (I think we were quoted something like $5k.) So with a great deal of help from Andy Pugh who kindly wrote a driver to bit bang the IO for the Adlink ISA card our machine used for the interface. I was able to get the machine running using software stepping and the original interface hardware, the same way the old DOS software worked. (We did have to buy a new ISA card because the old one fried with the old PC.) We ran it that way for a number of years, then I upgraded to a Mesa 5i25+5i85s to do closed loop step generation with encoder feedback. It is still running this way, and using the old ISA card for other digital IO, such as limit switches... If I were doing it over I would be ditching the old ISA card and either add a 7i84 for the digital IO, or simply used a 7i76 and left out the encoder feed back. (This would let me ditch the old P4 pc motherboard with ISA slots the machine is running now, and let me upgrade to current versions of Linuxcnc. I can't get anything newer than Ubuntu 10 to work on the old PC.)

The encoder feedback isn't nessisary but was nice to help with tuning the servo drives initially.

There is no driver to use the more current PCI cards that are used with Wincnc, they are somehow doing hardware step generation on that card or it's daughter board. And Wincnc is very secretive to how it and it's drivers work. So building a driver to work with Linuxcnc isn't going to be simple, or maybe even possible. But a conversion using just Mesa cards shouldn't be very difficult.

Exactly what interface hardware is there now? Photos of the boards would probably be helpful.
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16 Sep 2020 05:27 #182364 by spacemanspiffee

Thanks for replying!

I'm looking to basically replace the current motion control portion of the hardware with mesa and linuxcnc.
I'll probably keep the power supply and estop and whatnot and just figure out how to get all that hooked into linuxcnc properly.
I'd like to have the encoders feed all the way back to the controller because I am having issues with lost motion right now and having the loop closed as close to the controller as possible would give me the most confidence in eliminating those issues.
Would a 5i25 with 7i76 allow me to do that? do I need the 7i84 to get the encoder feedback to the controller?

Somewhat related, what is the benefit of going with a 6i25 over a 5i25?

Here are a couple pictures of the boards currently inside the controller:

Did you make new cables running to the servo drives when you retrofitted? And the drives you have are the SST-1500-UCX?

Again, thanks for the reply and I appreciate you taking the time to answer my questions. I'm excited to learn about all of this and I am a fan of linuxcnc, so I'm itching to get it onto my router.

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16 Sep 2020 17:02 #182449 by Todd Zuercher
Our drives are SST-1500, but are earlier models than the UCX ( ours are ACX), They are functionally equivalent though. I had to replace one of them once, and I think I might have use a UCX for the replacement.

The first board in the image is essentially just a breakout board, and does isolation and signal conditioning. It may also help process the PWM to analog signal for the VFD speed command. However it doesn't look like that is being used. Does your machine have a VFD?

I have the 5i85s mounted near the drive, and ran short cables from the drives to it. I don't remember if I made all new cables, or modified the old ones to add the encoder feedback. At the very least I had to add some pins to the old plugs and connect wires to them. (Probably just made new ones.)

Benefit of 6i25 over 5i25, it fits in a PCIe slot. I know of no other benefits.

For step/dir with encoder feedback on a simple router like this one of the most cost effective options might be to use a 7i96+7i89. If you need more IO then a 7i76e or 7i95 might be better. None of those options were available when I retrofitted this machine.

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16 Sep 2020 19:42 #182460 by spacemanspiffee
This machine currently doesn't have a VFD or real spindle. It's just got a router strapped to the front of it. This will change eventually, I'm saving up to put an ATC capable spindle on it.

The 7i95 appeals to me as a single board solution, but all of those combinations look good. With an Ethernet board, could I stick it into the box on the back of the gantry that has the drives in it and run a long Ethernet cable through the drag chain to connect to the computer in the control cabinet? Would that be an issue for signal integrity? This would mean the cabling I need to make to connect the mesa board to the drives is short. Do these cables need special attention paid to shielding?

Eventually I'm going to put together some form of ATC for this machine, not sure yet if it'll be wine rack or carousel style, but that is after I get the ATC spindle...
Would it be easier to implement that down the road if I went with the 7i76e+7i89 as opposed to the 7i95?

Thanks for the answers!

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16 Sep 2020 20:04 #182463 by PCW
Much better to keep the interface board to drive cables short
The Ethernet cable can pretty much be as long as you like

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16 Sep 2020 20:38 - 16 Sep 2020 20:45 #182469 by Todd Zuercher
Yes, you could mount it back there, and is probably what I would do. But remember most Ethernet patch cables aren't up to doing the constant flexing and pulling that is seen in a cable chain. Don't skimp, buy a good one that's shielded and rated for that kind of use.

I think the 7i76e+7i89 would be the best option with the VFD because of it's analog out put. But the other options could be just as serviceable. Especially if you use a modbus connection to control the VFD.

Some different ways to do this
7i96($119)+7i85($69) total($189) 5-step/dir, 5-encoders, 11-inputs, 6-outputs
7i92($89)+7i85s($69)+7i84($79) total($237) 4-step/dir, 4-ecoders, 32-inputs, 16-outputs
7i95($249) 6-step/dir, 6-encoders, 24-inputs, 6-outputs
7i76e($199)+7i85($69) total($268) 5-step/dir, 5-encoders, 1-analog out(0-10v), 32-inputs, 16-outputs

To do an ATC you will need a minimum of 2-3 inputs and 2-3 outputs just to do the tool release/purge of the spindle and reading it's related safety sensors. If you add a carousel that's a few more inputs and outputs and possibly a stepgen. This can eat up a lot of io pretty fast. But even the cheapest option above could be easily expanded by adding a 7i84($79) with 32-inputs and 16-outputs.

Also remember, simply adding encoder feedback may not help with your lost motion problem. The encoders used with these usually only have single ended ttl connections and are more prone to noise problems. If you are loosing encoder counts because of this closing the loop in Linuxcnc, could actually make your lost motion problems worse. But if the problem is with the ttl step/dir signals then going to true differential signals there and closing the loop in Linuxcnc would probably help.
Last edit: 16 Sep 2020 20:45 by Todd Zuercher.
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17 Sep 2020 00:34 - 17 Sep 2020 00:35 #182485 by spacemanspiffee
Ok, just to check that I am understanding what you're saying.

If my encoders are single ended TTL this makes them susceptible to noise and is potentially the source of my lost motion. Hooking this encoder feedback into LinuxCNC would not solve my lost motion problem and potentially make it worse.

If the encoders are not the issue, potentially it is the step/dir signal which may also be set up as single ended TTL. If this is the issue, switching this to differential TTL when I swap over to Mesa and LinuxCNC will help with the lost motion issue.

Are the SST-1500 capable of taking in differential TTL signals for step/dir?
How do I determine if my encoders are single ended?
Would the shorter connection from placing the mesa boards on the gantry help with issues in the step/dir signal (assuming that is the problem)?
Do you have a suggestion on where to get shielded, flex rated ethernet cable?

In regards to the Mesa boards:
7i76e has an analog out that is suited for driving the vfd
This would need to be paired with 7i89 or 7i85 for encoder feedback into linuxcnc
the other configurations you mentioned would require controlling the spindle over modbus or adding another 7i84 or similar

I think I'm leaning towards the 7i76e+7i89 because it looks like it will cover all the things I'd like to do in the future: spindle with vfd, atc etc.

Thank you for the thorough and clear answers. They have been very helpful.
Last edit: 17 Sep 2020 00:35 by spacemanspiffee.

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17 Sep 2020 04:30 #182500 by spacemanspiffee
So I did a bit of investigating and I believe my encoders are differential. The motor connector on the servo drives is set up for differential encoders and the manual for the SST-1500 mentions the motor model I have as being differential. This seems like good news in my opinion as it indicates the motion issue is in the step/dir signal. This can be fixed with LinuxCNC and mesa.

I also got a couple pictures of another board that is in the box on the back of the gantry right next to the servo drives.

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17 Sep 2020 12:36 #182540 by Todd Zuercher
Your lucky, the original motors used on my machine had single ended encoder signals. However I never had any issues with lost motion on either of our CNTMotion machines, because of the control.

Another thing to consider with lost motion issues is the possibly of a mechanical issue. Things like worn out belts with missing teeth, slipping couplers, pulleys, or gears on their shafts. I have had the teeth strip off of a belt before and cause all sorts of problems.

Are there certain conditions where you more often see the lost motion? Which axis?

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