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Stepper motors

Difficulty setting up to run smoothly

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Steve Pavey26/07/2021 12:43:49
369 forum posts
41 photos

This is proving to be a bit of a learning curve - I bought a little ds212 oscilloscope a few months ago which I haven’t used, until today that is. I hooked it up to the DIR and +5v terminals on the output of the controller, 5en used the controller keypad to run the X stepper left and right. The DIR signal is absolutely consistent - high in one direction and low in the other, irrespective of which way the stepper decides to turn**. I also looked at the PULSE signal and it displays a reasonably good square wave. I’m afraid I am not good enough with an oscilloscope to actually measure the voltage, but it’s clearly enough to run the stepper.

the other thing I wanted to do was to hook both up at the same time to see what the time relationship of the PUL and DIR signals was, but something didn’t like me doing that as the stepper didn’t run with both channels connected - maybe something to do with the internal resistance of the oscilloscope?? (Way out of my depth here, so I just disconnected it). I tested the DIR output with a multimeter and it was 4.8v which seems ok. I don’t think I would get a meaningful result doing the same on the PUL output.

I have tried setting both leading and trailing edge active in the controller software, without any difference to the random behaviour, so I’m not that much further forward, except I’m a bit happier that the controller is not at fault.

** To me this suggests that the stepper motor coils are not connected correctly, though I have checked many times that the wiring conforms to the supplied datasheet - https://cnc4you.co.uk/resources/Stepper%20Motor%20Nema%2023%2057HS82-3008B%202.2Nm.pdf

The Ruida user manual is at https://variometrum.hu/pdf/rdc6442g.pdf, though it’s a bit light on details related to configuration.

SillyOldDuffer26/07/2021 15:22:47
10668 forum posts
2415 photos

Baffling symptoms Steve!

Can you post photos of the wiring and your circuit diagram?

The misbehaviour of the oscilloscope may be a clue. As the oscilloscope's input impedance is about 1Megaohm, no way should measuring DIR and PUL together with it cause a problem. I wonder if the DM542 is wired correctly, because getting a pair the wrong way round would cause the symptoms. Note also the measurements are always taken relative to Ground, never between DIR+ and DIR- and Co.

The diagram in the manual is confusing because it shows the wiring done with shielded twisted pair, with the wires crossing over.

dm542.jpg

If the Controller is common-anode, PUL+, DIR+, and ENA+ must all be connected to Vcc (ie +ve)

If the Controller is common-cathode, PUL-, DIR-, and ENA- must all be connected to Ground (ie -ve)

What's not allowed is a mixture. Triple check the connections. A quick look at the Ruida manual suggests it's Open Collector, ie. Common Anode - Figure 3 applies, not Fig 4.

Dave

John Haine26/07/2021 16:07:16
5563 forum posts
322 photos

Just to be pedantic, the PNP signals are also open collector though common cathode (i.e. common cathode)!

Steve Pavey26/07/2021 16:21:27
369 forum posts
41 photos

Two things that I find mildly annoying - posts that ask questions but the final solution is never posted, and idiots who can’t admit when they’ve been really stupid.
So in order not to be guilty of both at once, and very red-faced, I think it’s confession time. I have some 4 pin plugs and sockets connecting the steppers back to the control cabinet. I had made such a neat job of these connections - all with heat shrink and numbered labels etc - that I left these alone yesterday when I did the rewiring. It turns out that one of the conductors wasn’t actually soldered onto the terminal, instead the tinned end of the wire had stabbed itself into the plastic and missed the terminal by about half a millimetre. Having melted itself into the plastic it survived my normal tug test, and once covered with heat shrink was out of sight.

A quick test once it was soldered up correctly and it works perfectly.

So, my sincere apologies for wasting everyone’s time - the only silver lining is that it was actually everyone’s responses that forced my brain to eventually work out where the problem might lie - ie that one of the coils wasn’t getting a signal. Actually, another silver lining is that I have at last used the little oscilloscope that I bought as a bit of an impulse purchase a couple of months ago.

Many thanks for everyone’s help.blush

479e900a-bf58-4880-bfab-02c28b959cea.jpeg

John Haine26/07/2021 16:55:18
5563 forum posts
322 photos

Excellent, glad it's sorted.

mgnbuk26/07/2021 19:20:29
1394 forum posts
103 photos

I have some 4 pin plugs and sockets connecting the steppers back to the control cabinet.

This isn't intended to be critical of you, Steve, as what you have done is what appears to be done often on DIY builds - but did you actually need a quickly detachable connection here ?

From a reliability perspective, every connection is a potential problem - your plug and socket introduces two soldered and one mechanical connection between motor and drive. Putting a gland in place of the chassis socket and routing the stepper motor wiring directly to the drive connector without any intermediate connections would have eradicated 3 potential trouble spots. This would obviously make removing the motor a bit more of an effort - but how often would you be doing that ?

On the drive systems used on industrial CNC machinery, it is not unusual for drive manufacturers to specify thet intermediate connections are to be reduced to a minimum, but preferably to connect the motor cable to motor at one end & drive at the other directlly. The fewer the breaks between the two the better & any joint that can be designed out can only be a good thing - particularly with soldered connections, which (in my experience) cause more problems than crimped.

In my previous employment (CNC retrofit & rebuild), warranty visits reduced when the drive manufacturers introduced pre-made & tested cable assemblies that were installed in one piece. Prior to that introduction, most issues when we made up cables ourselves (frequently broken at terminal strips for ease of wiring) had been caused at terminal blocks or soldered multipin connectors

Nigel B.

Michael Gilligan26/07/2021 19:49:17
avatar
23121 forum posts
1360 photos

Well done, Steve ... They do say that Confession is good for the Soul

MichaelG.

Steve Pavey26/07/2021 22:31:51
369 forum posts
41 photos
Posted by mgnbuk on 26/07/2021 19:20:29:

I have some 4 pin plugs and sockets connecting the steppers back to the control cabinet.

This isn't intended to be critical of you, Steve, as what you have done is what appears to be done often on DIY builds - but did you actually need a quickly detachable connection.. etc

Nigel B.

You’re right Nigel. I did think about this early on in the build, but it really had to be like this because of the space restrictions in the workshop, and the need to have the machine on castors, along with a control cabinet fixed on the wall. I also used some decent connectors from RS rather than cheap imports from you know where! Of course, as you now know I was let down badly by the bloke doing the soldering! At least I know where to look first if a similar problem arises in the future.

John Haine27/07/2021 10:18:45
5563 forum posts
322 photos

I use XLR 4-pin connectors for all but 3 of the 9 steppers I'm using in the workshop. The 3 are the XYZ axes of the Novamill, and those are connected by a big multi-way plug and socket originally specified by Denford. So far in 10+ years I haven't had any problems with them.

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