Cuts not repeatable, I'm losing steps

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tblough
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Re: Cuts not repeatable < overall turns ratio >>>not the problem, I'm losing steps

Post by tblough »

lavrgs wrote: Thu Jan 06, 2022 7:53 pm ...but my understanding was that the resistor in the DMM cable brought 24V down to 5V - I may be wrong, it happened once before. Is this NOT a noise issue?
With a plain DC circuit, a resistor does exactly what you describe; it drops voltage, regulates current, and dissipates the extra energy as heat. Once you add a signal to that DC circuit, it begins to operate more like an AC circuit and now you get impedance, inductance, reflected signals and a whole bunch of other troubles due to that resistor.
Cheers,

Tom
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I have CDO. It's like OCD, but the letters are where they should be.
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Re: Cuts not repeatable, I'm losing steps

Post by slodat »

DMM was of no help to me. And, when I was going through this many folks on here kept telling me to use the screw terminals. I went to great lengths to diagnose this, develop a meaningful test, and then make the change and see the improvement. I don't care what you do. I do know that for me, on the systems I've built, using the DB25 step and direction signals, as I have documented in my thread(s) about this has worked flawlessly.. going on three years.

DMM has refunded my money for their cables, twice. I won't make the mistake of buying the cables again. Anyway.. that's my experience.
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Re: Cuts not repeatable < overall turns ratio >>>not the problem, I'm losing steps

Post by slodat »

tblough wrote: Thu Jan 06, 2022 8:16 pm
lavrgs wrote: Thu Jan 06, 2022 7:53 pm ...but my understanding was that the resistor in the DMM cable brought 24V down to 5V - I may be wrong, it happened once before. Is this NOT a noise issue?
With a plain DC circuit, a resistor does exactly what you describe; it drops voltage, regulates current, and dissipates the extra energy as heat. Once you add a signal to that DC circuit, it begins to operate more like an AC circuit and now you get impedance, inductance, reflected signals and a whole bunch of other troubles due to that resistor.
Exactly, Tom. Add to it the difference in the way the two sets of step/direction outputs work and Bob's your uncle.
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Re: Cuts not repeatable, I'm losing steps

Post by Richards »

I agree with Keith's instructions on how to determine what causes the problem. If you find that electrical noise is inducing signals onto your Step/Direction signals, finding a fix might be a little intimidating.

I only have one DMM DYN4 750w driver/servo on my test bench. When I was testing it, it seemed to be sensitive to electrical noise. However, I stopped experimenting before trying some common LVDS differential line drivers/receivers. Those line drivers/receivers cost about $1.60 each from Digi-Key or Mouser. Rather than trying to explain the theory behind line drivers/receivers, spend a few minutes on YouTube and watch a few tutorials. Once you understand what differential line drivers/receivers do and how they can reduce noise on the step and direction lines, the next step would be to buy an assembled board or build a prototype board of your own. Unfortunately, a quick search on Mouser showed that the differential drivers/receivers that they have in stock are NOT the easy-to-use DIP chips. Instead, they stock surface mount parts. Surface mount parts are perfectly usable in a prototype circuit, but you'll need to solder wires directly to the pins.

The way I look at it is that a control box can generate a lot of unexpected electrical noise, especially if you have a VFD inside the box. Even without a VFD, switching power supplies generate electrical noise. Relay contacts generate electrical noise. Power cables from the stepper/servo drivers to the motors generate electrical noise. Suppressing noise from all those sources (and many other sources) might leave you as bald as I am. The better idea might be to drive the step/direction lines with differential line drivers/receivers that automatically reject most of that electrical noise.
-Mike Richards
lavrgs
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Re: Cuts not repeatable, I'm losing steps

Post by lavrgs »

cnckeith wrote: Thu Jan 06, 2022 7:10 pm and related diagnosis procedure i use.

pull the axis motor that is having issues. mark the shaft. zero the DRO position at the mark. run a test program. (typically moving large distance and then back to zero at different rates) does the motor return lined up with the mark when program is done?

if yes, then edit the test program to turn on and off the spindle and any other accessories you have connected to the cnc controller, run the test again. if you lose steps with this test it is related to noise. make sure to have quencharcs on all contactors and solenoids, reevaluate the wiring practices for grounding and shielding.

if no, then the lost steps is related to that axis, swap the drive wiring on the acorn to another axis and run same test. does it follow the move? i.e. does it still not return to the mark while using another axis? if yes, then you have isolated the cause of the issue to the motor/drive/cabling. replace cabling/drive/motor to further isolate the issue.

if the motor/drive passes all the tests above check the mechanicals, loose pulleys and couplers that move during a rapid but will hold just fine during feedrate moves are common issue that mimic lost steps. use sleeving locktite on problem pulleys/couplers like this. i use 620 found at the bottom of this page. https://www.centroidcnc.com/centroid_di ... _gear.html
I use DMM's App DMMDRV to check for lost steps. When driving the motor with their app alone I can move and return to zero. When I drive the axes with acorn the DMMDRV app shows that I do not return to zero. I prefer to have the motors under load and I know that 8000 steps is one rev of the motor. My test was to have the axis cycle from -2 to 2 25 times. When I start I know I am at ZERO via the app, and after the test I was > than 4 turns from 0, which is greater than 0.100 inches. THIS SOUNDS LIKE LOST STEPS...This is using the DMM cables and when I get new cables the BIG question is do I run the wires to a breakout connector and into the Acorn DB25 Connector? and rerun the test.
EDIT CHANGED BREAKOUT BOARD TO BREAKOUT CONNECTOR
Last edited by lavrgs on Fri Jan 07, 2022 1:51 pm, edited 1 time in total.
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Re: Cuts not repeatable, I'm losing steps

Post by ShawnM »

This comment isn't meant to help with the OP's issue but rather let you guys know something about the new DYN5 drives from DMM. Maybe they have been listening to these issues. First, I have not seen the wiring diagram for the DYN4 drives to compare the wiring but I do know they only list DIR+ and PUL+ on the JP4 connector. I'm using the new DYN5 drives and they have BOTH PUL+ 24v and DIR+ 24v inputs AND a PUL+ 5v and DIR+ 5v input pins on the JP4 connector. This way you can use either input without any resistors or resorting to the DB25.

I have been bench testing these for a couple of weeks while I was getting the machine ready for the new DMM motors. I have the drives hooked to the Acorn headers wired to the 24v inputs on the drive. I finally have them mounted to the machine I'm retrofitting and will be powering them up tomorrow for testing. Once powered up and tuned I'll run the same -2 to 2 test 25 times and see if I lose any steps hooked to the headers.

There are MANY improvements to the DYN5 drives over the DYN4 and you can also get an Ether CAT version as well.

Again, I know this doesn't help with the current topic but I wanted to share info about the DYN5 and hopefully this issue of lost steps wired to the headers has been solved going forward with true 24v inputs on the drive without the need for a resistor.

Also, DMM is also NOT making cables for the DYN5 to Acorn for the record. I didn't buy ANY DMM cables as I'm reusing the very nice OEM shielded cables that came on this machine. I was able to reuse the shielded motor power, drive power and encoder cables that came on this machine. I just chopped off the old connectors and bought only the DYN5 connectors from DMM to make all my own cables to my custom length.

I'll report back over the weekend about my testing and if any steps were lost using the headers with the new DYN5 drives with true 24v PUL and DIR inputs.
lavrgs
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Re: Cuts not repeatable, I'm losing steps

Post by lavrgs »

DMM has an interesting take on these issues which I haven't seen come out yet...from the Centroid side
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Re: Cuts not repeatable, I'm losing steps

Post by cnckeith »

i'm about to pull support (our DYN4 schematics and DYN4 drive type from the wizard) for the DYN4.
countless hours spent on this forum trying to solve DYN4 related problems.
I would use another AC motor/drive. Estun, Delta, Yaskawa, Clearpath you name it, they all work great.
Maybe the DYN5 is great? I sure hope so.
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
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Re: Cuts not repeatable, I'm losing steps

Post by Chaz »

cnckeith wrote: Fri Jan 07, 2022 2:45 am i'm about to pull support (our DYN4 schematics and DYN4 drive type from the wizard) for the DYN4.
countless hours spent on this forum trying to solve DYN4 related problems.
I would use another AC motor/drive. Estun, Delta, Yaskawa, Clearpath you name it, they all work great.
Maybe the DYN5 is great? I sure hope so.
So interesting to see this. I cant help but think some of us said 'I told you so' when we used to 'muse' on why so many people seemed to struggle with that manufacturer vs others despite support on the forum for them. Clearly the evidence is there and the tribe has spoken.
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Re: Cuts not repeatable, I'm losing steps

Post by slodat »

The advantage is DMM makes motors that bolt up to standard NEMA sizes. And, they work great when connected to DB25 on Acorn.
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