Closed loop stepper cable questions...

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06 Mar 2022 10:18 #236493 by harmo
Hi All,

I hope you're all well. It's been quite some time, but I'm back where Internet isn't just a dream, and cows aren't part of my daily routine.

So here's the situation:

When I get a few spare moments, I keep tinkering on my CNC control box. The box is nearing completion... well.. the end is in sight at least... but I have a few testing problems...
  • I have some Stepper Online CL86Y closed-loop drivers and matching 12NM steppers. When using the usual 1.7m Stepper Online power/encoder cables, connected directly to both motor and driver, everything works fine.
  • I need to have detachable wiring between the control box and the machine for storage purposes. So my intent is to have the encoder and power cables running between the driver and stepper go through sockets mounted to the chassis of the box. The theory is.... I'll use the usual 1.7m Stepper Online cables to go from the driver to a socket on the chassis, then from there, use the 4.7m cable to connect the machine.... although I'll have to solder the requisite aviation/VGA plugs to the bare wire end so it connects to the box.
  • I've tested the aviation sockets (they run motor power) mounted to my chassis, and when I plug the motor into them, it works. However, until today, I just ran the encoder cable direct from the driver to the motor. (No socket or chassis mount yet).
It all seemed simple enough.... so I mounted the first encoder cable to the chassis, and decided to do a test before I got much further.... this proved helpful, as I ran into problems straight away.

So some more facts:
  • I put the stepper power sockets on one side of my CNC control box, and the encoder cables are mounted on the other side of the box. Just trying to distance the power circuitry from the lower voltage signalling stuff.
  • Noting that the distance between the sockets is quite large, and that I haven't terminated the 4.7 cables (encoder/power) with their respective male plugs, I plugged the motor directly into the power socket on the left side of my control box, and ran a standard VGA extension cord to bridge the gap for the encoder cable socket (right of the control box) back to the motor.
This had some unexpected results:
  1. The motor moved a tiny bit (a fraction of one turn) when jogged in LinuxCNC, then never moved again, until the whole system (control card, drivers, et al) was shut down and restarted. Same thing happens every time.
  2. The driver did not show any indication of alarms, (no flashing red LED) and LinuxCNC kept sending signals as though nothing was wrong.

Hypothesis One: The ferrite beads on the VGA extension cable may interfere with the pulsed voltages of the encoder.

.... so I removed them from the cable, just to see what happened....

Result:

The motor turned momentarily like before.. maybe for twice as long (roughly half a second to a second), but instead of simply stopping, it started to hum (but no rotation) as though it were fighting against itself. Again no alarms or errors on the driver, it just hummed there until I either disconnected the encoder cable, then the alarm LED started flashing... or the whole system was powered down and restarted.

Hypothesis Two: Maybe I made a mistake when wiring the chassis mounted socket?

I took a known-good cable, mounted it to the chassis, then plugged the extension cord to the motor and tested.

Result:
No change. This cable worked perfectly when directly connected to motor, but mounted and used with the VGA extension cord, the same thing happened. So hopefully it means my first mounted cable is good.

Hypothesis Three: VGA extension cable defective?

Swapped it out with a new, ferrite covered cable....

Result:
Back to silent stopping. So no change.

This is where I'm up to... but I've been thinking (always dangerous :-D )

Hypothesis Four: VGA cables simply aren't good for encoder signals....

Intended procedure: I'll try soldering a male VGA plug to the 4.7m StepperOnline cable and see if that helps. Don't have a spare VGA plug... so that's on my shopping list.

Hypothesis Five: Chassis mounting a bad idea?

This is where I humbly ask if anyone else is mounting motor cable sockets to their control boxes? Am I missing something else here? Some common sense knowledge that has somehow eluded me to this point? Am I deluding myself into thinking that I can have detachable connections on my control box?

I'm actually building the control circuitry into a mobile trolley/cabinet of sorts, computer on top, but all the sensitive/dangerous electrical stuff locked away.

Any thoughts would be welcome. I know I am always asking for advice whenever I'm able to reach the kitten-mangled ball of yarn known as the Internet, and I hope one day to provide it to others here.. but that might have to wait until my skills are up to that task.

As always, thank you for reading and I hope this helps someone else in the future.

Have fun and enjoy CNC'ing weird and wonderful stuff!
Hamish.

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06 Mar 2022 10:46 #236495 by rodw
Are you using 15 pin VGA connectors or 9 pin DB9's? VGA seems to have too many signals for an encoder.

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06 Mar 2022 13:51 #236503 by tommylight
VGA cables are very good for encoders, but the pinout might be wrong so it will not work. Or maybe it will...?
Check online for pinouts, if the encoder A, B, and Z are on the R, G, B pins on the DB15 ports, that is good. Anything else will not work.

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06 Mar 2022 22:17 #236537 by harmo
Hi Rod,

I hope you're well, and thanks for getting back to me. It's the 15 Pin VGA plug. You're absolutely right that it has far more than the necessary 6 wires of the coder. According to StepperOnline documentation, it uses pins 1-3, and then pins 11-13 (inclusive on both ranges). The rest are completely unused.

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06 Mar 2022 22:48 #236539 by harmo
Hi Tommy,

As always, thanks for your response.

I guess my concern was that VGA signalling might be "lower voltage/current" than encoder signals...so the cables (or the cores, more specifically) would be too thin, or operate at some sort of odd EMI/RFI inducing frequency.

Interesting thought about the pinouts. I could possibly understand if they're male-to-male or female-to-female (mirror image of pinouts so the socket and plug pinouts match). However, I would have hoped (perhaps stupidly) that a VGA extension cord would keep the pinout consistent. That's an assumption I have to verify.

Thanks for the idea, I'll definitely check it out.

P.S. I have been instructed by the mini-matriarch of my household to convey a request:

"Please give your dog pat for me?". (Her words)

Anyway, thanks for the guidance, I'll report what I find.
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06 Mar 2022 23:45 #236542 by tommylight
You are welcomed, always.
And i can not pat that dog anymore, it ran away ! :) It was not mine, it just lived on the streets and we would feed it so he was around for several months, then one day he was gone, pretty sure it had something to do with a woman or a pack of cigarettes! :) I do have a white one at home and i think there is a picture in the build log thread/topic here from when she bit me and then ate a brand new Lenovo laptop power supply.
forum.linuxcnc.org/show-your-stuff/38547...ild?start=110#171915
Now that you are done with "aaahhhhh", bite marks! :)
forum.linuxcnc.org/show-your-stuff/38547...ild?start=110#172157

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08 Mar 2022 11:42 #236661 by harmo
Hi Tommy,

I can only interpret that as you clearly weren't feeding your pup enough Lenovo branded "Charger kibble", the lack of power in the relationship must've been something that needed to be addressed. Although I don't approve of his violent coup d'état (that's apparently French dog for bite. :-)

The mini matriarch here is both approving of the "white fluffiness" and in her animal obsessed way, asked if the puppy is ok after eating the charger.

Back to me though, because I'm more qualified to talk about that than most stuff here...

Well after muttering incomprehensively for hours in the garage, (and only incidentally testing stuff) I have learned a few things:

1. Some variations of VGA extension cables don't use pin 11 or 12 (one of the 6 pins chosen by StepperOnline to wire their motors through. I had no connectivity on pin 11.... so.... that was suggestive of a problem.

Moral to this story, don't assume every VGA extension cable will work as encoder cables. I had one type with no connection on pin 11, another with no connection on pin 12, and another with no connection on either.

Why oh why didn't StepperOnline use the commonly used pins?.. or better yet, an RS232 or DB9 plug (all the pins are wired).

2. I am truly abysmal at soldering VGA plugs. I used a length of CAT6 cable, and a male/female pair of VGA (DB15HD) plugs to create a test "extension cord" for the encoder. I certainly wouldn't use it in a production environment... but it's something some others building their DIY CNC might consider "a factor" when buying a closed loop stepper kit.

3. My 20 year old, beaten up, "Fat tipped" 40W soldering iron is probably not the best piece of kit for finer soldering work. I'm honestly surprised I've gotten this far with it.

....Frankly, a few VGA male and female plug to screw terminal boards are looking pretty good about now.

Anyway, I have tracked the problem down. Thanks for the suggestions!

P.S. I have to say that I'm not overly convinced about Stepper Online's closed loop cables at this point. A little thought could make them SO much better (longer thread on the aviation plugs so we can mount them to cabinets thicker than 0.5mm, offering an honest to goodness extension cord with a plug at BOTH ends, proper shielding with earthing points... you know.. stuff that helps... a lot).

Anyway, I'm probably going to be making my own cables, from here... so maybe others can save themselves some pain and might consider doing the same.

I hope the somewhat painfully earned lessons help someone else out there.

Take care.
Hamish
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08 Mar 2022 14:17 #236674 by itsme
I would say StepperOnline did well preventing People using Standard VGA extention cables. These cables are not intended to be used in drag chain environment.
So preventing the use of this cables is preventing problems.

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08 Mar 2022 14:44 #236677 by rodw
Ovi Hiris at treotham.com.au could help with drag chain compatible wiring...
 

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08 Mar 2022 23:22 #236723 by harmo
Hi Itsme,

You raise an interesting point. Others will no doubt find it helpful. However, I'm sorry, I left some key information out of my description. I did not mean to suggest using VGA cables in the drag chain as you inferred. That's my fault.

So let's be clear here:

My CNC router design has a control box/trolley that's completely separate and detachable from the machine. This is mostly for storage purposes, but could enable the control system to be moved and linked up to differing machines (obviously one at a time, with individual LinuxCNC configurations) and/or repurposed easily without significant internal rewiring.

Back to the VGA cable:

I'm not trying to use the VGA extension cables in the drag chain, merely to bridge the gap between the wall mounted sockets of my control box, to another bunch of panel-mounted sockets on the device itself. Using a VGA cable for this purpose shouldn't have the constant flexing that the drag chain that you're worried about.

From there, the usual Stepper Online provided cables will be used in the drag chain.... Or at least, that is the current plan. I wanted everything to be modular so storage, diagnostics and replacements were easier.

Of course, this is all theoretical at present... I'm only using the VGA cables for testing motor connections/function as I have no machine, or even drag chain at this point.

I hope that clears things up, and I will try to be clearer about what I'm trying to do in future. Your thought about NOT using VGA in the drag chain was a good one.

Kind Regards,
Hamish.
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