Y axis is making X axis stall...!!

Hi all..

One day, in the dim and distant future, I will finally kick all the bugs outa this cnc build, but not today it seems...

When I am jogging the x axis (dual drive nema 34's, slaved together in Mach3) it moves freely, until I try to also move the y axis simultaneously.. Then an awful grinding noise and the x axis completely stalls (no movement)... First picked this up last week when it was cutting a circle and it was rapid moving (G0) to the next cut, it stalled the x axis and therefore did not move to the right place..

I have since redone all the wiring and triple checked all mechanical movement which has made no difference, in fact I would say it has got slightly worse if anything..

I am using a Uniport controller, 2 x PM752 drivers (x-axis) and a PM540 driver for the y.. I have wired it all according to the plan shown here..

Attachment 4686

Anyone encountered this before? Any ideas? Wanna lend me a really big hammer..?


Steve..

Just to mention, I have reduced the motor tuning speeds and accelerations in mach3 until it now crawls at snail speed, no difference...


Steve..

Is the power supply man enough as your simultaneously driveing 3 motors when you move both X and Y.
Just a thought as I assume each drives well on their own.

Peter

If you'll forgive my ramblings, do you get the same problem with X and Z?

Hi guys..

In order..

PSU has plenty of power, am using a 55v 5amp for the nema 34's, and a separate 24v 2.5amp for the nema 23 (y axis, 3Nm)...
Dont get the same prob with the z and x... Only the x is stalling... And only in rapid, regardless of what I set the motor tuning to...



Steve...

it could be the psu? can you measure the DC voltage on the driver and see if it drops when you move the other axis? Also are you daisychaining the DC or comming back to a star point?

Steve,
what current setting do you have the drivers set to?

Ian

Hi again..

Just gonna pop my lad to bed then will check what you guys have asked/suggested..

Steve..

Hi again..

Bit more info on the problem.. It only seems to happen when moving x and y in full rapid, if one or other of the axis is not moving at full speed it does not happen i.e. it happens when rapid at 45 degrees, but not 30 degrees... If that makes sense... Sorta guessing both motors are at full throttle when moving at 45 degrees rapid..

Some more info on my setup..
X axis is a pair of SY855TH80-5504B steppers driven by a pair of PM752 drivers.. The settings on each driver is;
3200 microsteps
5.5amps

Y axis (and z) is a 3Nm nema 23 (from Zapp) on a PM540 driver, settings are;
3200 microsteps
2.5 amps

Got my specs wrong on my PSU's earlier, should be;
X axis run by a single PSU (separate outputs) which delivers 65v 8amps..
y and z share a 24v 4amp PSU..

Will test voltages tomorrow when I can get a new battery for my multimeter...
Am 99.9% sure it is something electronic as I have torn apart and rebuilt every mechanical part and everything is freely moving.. Also, I am a decent engineer and a crap electrician with only slightly more knowledge of electronics than my cat...

Steve..

Just a thought...

Have been roving around all the cnc forums trying to find another with the same probs... I have seen an awful lot of posts about earthing, but I have to say, as a complete burp at electronics, I ended up more confused than when I started... Cant get my head aound the myriad of different advice being handed out, and much of it was american.. Do they use different terms for all that common,starpoint,earth,neutral,-ve supply/rail,0 volt stuff? Damned if I can work out what they are in English without even more varying terminology.. I ramble..

Does seem to be a big cure-all for a lot of electronics issues so I was wandering if there is a good post/guide to earthing for us feeble minded noobs? From what I have read, I ought to do this as a matter of course, if only to eliminate several potential problems...

Steve..

Seems to me that you have several issues that could and will be causeing this problem. . . First reduce the microstepping to 2000. Not much to gained above this it will also ease the PP work load. . . . Also good idea to run the driver test in Mach folder to test how well your PP works.
Then re tune your motors and see how it performs.

Next 24V is way too low for these motors and will restrict rapid speeds, this would be the first place I would turn to. . . . You could easily double this figure with these motors (If the drives can handle it)

Regards daisy chaining and grounding etc it's not really rocket science but is important if you want to restrict potential problems.
Basicly when running power from the power supply you want to run a separate wire to each drive not 1 wire to first drive then jump or "daisy chain" from this to next drive.

Think of the PSU as the centre of a star with all single wires running from it out to each component that needs to takes power from it.

The same applies to the ground wires, run each ground back to 1 central ground point. It's a good idea to have single ground connector with multiple connections, basicly you dont want multiple ground points around the machine other wise you can introduce ground loops which can cause noise issue's. Thou I'm pritty sure this is not your problem.

Their is another potential problem that can cause what you are experiencing. . . Mid band resonance.!!
This is caused by resonance from the machine which at a certain point in the accelleration curve interfears with the pulse stream going to the motors causing all sorts of random issue's.! rough sounding motors and poor performance as well has stalling as the speeds increase are just some of them.
Some drives have compensation for this built in some don't.! . . Not sure if yours do or not.?

If I was to place a bet on your problem I'd put money on it being down to 24V supply. . . And possibley too high on the stepping.

Also what Kernal speed are you running Mach at.?

Wow Jazz.. Lots to chew on...

Ought eliminate a couple of potential probs tho... I am not daisy chaining the motors/drivers with power, all have there own separate feeds/wires.. Not sure what the voltage limit is for these motors and I have been frowning a smidge at the 24v power supply as a possible weak point.. But the y axis is not stalling, and my last cnc was driven by just that one 24v psu, and it drove 4 x 3Nm motors then with no probs like this one...

Was running Mach3 at 25Khz, ramped it up to 45Khz in trying to fix this prob and it made no difference (using a dual P4 board, 2 gig ram with XP in desktop PC mode) so I left it at 45KHz..

Driver test is fine..

By ground, you mean earth right? Connect 0v and or ground to earth? Read this many times but when I look into my box of tricks, there are an awful lotta grounds and 0v points, more if you eyeball the PSU's too.. Pass the aspirin...

Mid band resonance... Is this a resonant frequency of the machines mechanical structure? If so I doubt this is a problem as the motors are very smooth and pretty quiet (apart from that dull thump caused by backlash comp in Mach3) until the very sudden growl from the nema 34's when they stall.. The fact that they both stall, and bearing in mind they are slaved together in Mach3, still suggests something electronic tho... Also as both the y and x are running at full speed simultaneously suggests it might be power, so will get a new battery for my multimeter first thing tomoz...

Will drop the steps as you suggest and check some voltages in the a.m. Starting to get intrigued by earthing, really feeling the need to get that one outa the way..

Steve..

Quote:

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Originally Posted by fasteddy

By ground, you mean earth right? Connect 0v and or ground to earth?

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Yes by ground I mean Earth.
One Earth point which each mains device leads back too or picks up from.

Basicly all roads lead to Rome or in this case one earth point.

Are your phase cables and signal cables shielded?
If not you may find that noise is being picked up on the signals.
This may be hitting the direction signals and causing one of the x axis to be changing direction?
disconnect the direction signals on the x axis and see if it still happens.

Hi Gary..

Cables are shielded, still troubling me that only the x axis is stalling.. y is unaffected yet is obviously part of the problem... sigh..


As I have got you here, what is the voltage rating for the 3Nm nema 23 motors you sold me? Has been suggested I may need to upgrade my
24v PSU for them...

Steve..

Chicken or egg?

Not sure if the problem caused this, or if this is the problem... On the power supply for the nema 34's (x axis), I have just discovered a 'crispy' component.. Think its a resistor, I can only read '8K' on its blackened surface.. I was about to check voltage outputs from this PSU when I saw a tiny wisp of smoke come from it.. I have switched it all off and will contact the chap that sold it to me to see if he knows what it is..

Steve..

Quote:

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Originally Posted by fasteddy

As I have got you here, what is the voltage rating for the 3Nm nema 23 motors you sold me? Has been suggested I may need to upgrade my
24v PSU for them...

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I run mine with the same PM752 drivers on 70V, so you can easily increase yours which will make a huge difference to the speeds you get. You can use up to 50V for the motors on the PM542... 48V is common and convenient. Easiest option is probably to get a big toroidial transformer to run both on 48V, but it would be better (faster) if you had two transformers to get 48V and 70V. There used to be someone selling lots cheap power supplies on eBay which were just under that voltage and ideal for this application. They've all suddenly gone now but you can buy them from Zapp for several times the price.

I did have a similar problem to yours at one point...
Since you're saying that X and Y both go at highest speed when moving at 45° you must have their feeds set the same. On my router I started with X a little slower than Y, so to get both to move at highest speed (which makes the actual speed the vector sum of X and Y maximum velocities) I had to move it at a different angle. At that angle or close to it the machine would often stall. The first thing I tried was to reduce the feedrate further on X from about 10m/min to 8m/min then 7m/min which each helped (stalled less often), but that was getting a bit slow...I had a spare transformer, so added that in to power the Y (and A) axis and left both the X's and Z on the bigger transformer. That makes the two axis independent, so from the driver's and power supplies point of view it's no different if one is drawing a lot of current or both. The voltage wont drop.
This didn't make a lot of difference, so I analysed both set-ups with oscilloscope. I can't find where I saved the graphs, otherwise I'd post them ... but it did show there was some ripple (couple of volts I think) with both setups and the ripple was slightly less with them split. Still evidently it was not enough to make much difference anyway.
Since that implies the power supplies were only a small part of the problem I decided to finally get round to swapping the computer to a better one I had (1.4Ghz AMD to a 3Ghz something or other), which made a massive difference. Feedrate on X went up from barely reliable at 7-8m/min to fine at 15m/min! It almost doubled the feedrate ... purely due to the computer's evidently better parallel port as I kept everything else the same. Since then I have increased the kernel frequency to 35kHz as that's sufficient to use 1600step/rev. You only need to use the minimum kernel speed to get the feedrate you require at the chosen microstepping value, so having it at 45kHz versus 25kHz is pointless and unnecessarily unstable if the former is sufficient.

Putting a bigger capacitor on the power supply may help, depending on what the value is currently?
Definately use the driver test in mach3 to check the parallel port. Perhaps try another computer?

Quote:

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Originally Posted by fasteddy

Chicken or egg?

Not sure if the problem caused this, or if this is the problem... On the power supply for the nema 34's (x axis), I have just discovered a 'crispy' component.. Think its a resistor, I can only read '8K' on its blackened surface.. I was about to check voltage outputs from this PSU when I saw a tiny wisp of smoke come from it.. I have switched it all off and will contact the chap that sold it to me to see if he knows what it is..

Steve..

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Ahh must be a switching power supply, good luck getting that fixed. If something has gone wrong with the regulation circuit that would explain your problem.

I forgot to mention in my previous post that the stalling only occurred with mine at or near full speed, and completely went if I made X really slow (it was always X that stalled). This doesn't seem to be the case with yours... so I'm not sure. Maybe try wiring both X drivers to the same step/direction pins on the parallel port and disable the slaving as that should reduce the 'load' on the parallel port.
Also remember that the average current drawn by the stepper motor is not a simple function of speed...

Hi Jonathan..

I have just emailed you and tried to telephone you.. It is the PSU I bought off you that has the crispy component..! Check your email..

Steve..

Quote:

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Originally Posted by fasteddy

I have just emailed you and tried to telephone you.. It is the PSU I bought off you that has the crispy component..! Check your email..

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:redface:

That'll be the bridge rectifier then. I put two capacitors and rectifiers on the transformer as it has more than one secondary. Were you using both (one for each motor) as I think that's what I said to do to share the load? Looks like it needed a heatsink, unless something else caused it. I can post you another (this time bigger) bridge rectifier so you can solder it in? I've got to go to a lecture quite soon... I'll give you my mobile number so you can call me after about 5pm.

It's strange as that's the same bridge rectifier as I'm using, and mine has ran 4 of the 3Nm motors just fine for a long time, which adds up to a lot more current than the

I think transformer gives 40VAC, so about 55V DC... can remember exactly. Either way it's a lot more than 24V.

Hi Jonathan..

Just emailed you again;

Just had a real close look at it with a loupe, I can see a single strand of wire from the +ve very close to the –ve.. Reckon it may have been arcing.. Tried to take a pic for you but my camera/phone cant take pictures that close and all I could get is a blur..


Part of me is relieved as this could well be the source of my probs... You set the the PSU for two outputs, 65v 8amps which I am pretty sure is fine for those motors.. Yes please, if you can send me a replacement rectifier, I will solder it on.. The -ve wire is also crispy so will replace that too...

Steve..

Quote:

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Originally Posted by fasteddy

You set the the PSU for two outputs, 65v 8amps which I am pretty sure is fine for those motors.. Yes please, if you can send me a replacement rectifier, I will solder it on.. The -ve wire is also crispy so will replace that too..

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Ok, I've got a few 35 amp ones lying around which should do the trick.

I'm a bit worried now you appear to be using this power supply with the PM542 drivers? I thought is was PM752. If that's the case it's bad as those drivers are only rated for 50V. I'll check in our emails what voltage the transformer actually is/was.

EDIT: Nevermind, that's me being an idiot...it's the PM752 so not a problem.
I really need to go now.

Hi Jonathan..

No, I am using your PSU for a pair of nema 34's, which are run by a pair of PM752 drivers.. Think these are rated at 70v and have run them well till now.. Have just been reminded that I moved the PSU last week, perhaps I jogged that single strand of wire...?

Steve..

Hi all..

Jonathan gave me a quick fix for the PSU so am up and running again.. But the problem of the x axis remains, so please dont give up on me all you CNC gods out there...

Steve...

Steve

I have one of the PSU's that Jonathan is talking about (the ones off eBay).


I have to have a clearout so if its any good to you make me an offer.

I have not used it, just powered it up to make sure all is ok when I first got it.

Regards

Andy

Quote:

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Originally Posted by audioandy

I have one of the PSU's that Jonathan is talking about (the ones off eBay).

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I'll buy it if Steve doesn't, but it looks like his needs are greater. I'm guessing as it says you're also in Nottingham there would be no need to post it...

Ok Jonathan

No problem, let Steve have first call then it's over to you.

Regards

Andy

ps I'm in Sutton-in-Ashfield just off Junc 28 M1

Same/very similar problem here. When jogging an X-Y table with MACH3 at full speed (400mm/min) in either the Y+/Y- direction and then, at the same time, attempting to jog either X+/X- at full speed [and completely vice versa] there are a lot of loud horrible mechanical noises and the table clearly stops moving correctly. This is 100% repeatable. Not seen this happen when machining a piece - that said I'm not aware of a situation where the machine is asked to move full speed in, say, the X direction whilst it's already moving full speed in the Y direction. I assumed - for no good reason - that this was a MACH3 jogging thing. So now I'm very interested in the answer.

Setup:
Motors: SY60STH88-3008BF (x3)
Driver: PM542 @ 1,600 pulses per rev, 2.37A(Peak) [1.69A(RMS)]
Supply: 43V
MACH3 motor config': 627 steps per mm, 400mm per min

Quote:

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Originally Posted by Karl

I'm not aware of a situation where the machine is asked to move full speed in, say, the X direction whilst it's already moving full speed in the Y direction. I assumed - for no good reason - that this was a MACH3 jogging thing. So now I'm very interested in the answer.

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Nothing to stop you running a program like this. It's conceivable on a drilling cycle.

G21 G61
G0 X0 Y0
G0 X100 Y100
G0 X0 Y0
G0 X100 Y100
G0 X0 Y0
G0 X100 Y100

Quote:

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Originally Posted by Karl

Setup:
Motors: SY60STH88-3008BF (x3)
Driver: PM542 @ 1,600 pulses per rev, 2.37A(Peak) [1.69A(RMS)]

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You and Steve are both running these motors in Bipolar series, not parallel ... interesting.

Quote:

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Originally Posted by audioandy

No problem, let Steve have first call then it's over to you.

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Thanks :)

Hi Karl..

At last! Someone with the same problem.. I ran a piece of code last week with 16000 lines and it was not until near the end that it stalled my x axis.. The code was making a rapid move at 45 degrees for 11mm and then stalled the x axis.. I have now spoken to several people about this problem and between us have eliminated most of the potential problems.. What remains is;

Re-install Mach3 including driver..
Trying a different PC in case it is the parallel port..

I will dive into the workshop and try both these things and report back any success/failure..

Steve..

Hi Jonathan..

I had always thought bipolar series was preferred to get the higher speeds? Is parallel better?

Steve..

Quote:

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Originally Posted by fasteddy

I had always thought bipolar series was preferred to get the higher speeds? Is parallel better?

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Yes parallel is generally faster. Bear in mind the current the drivers is set to also makes a difference as the torque is roughly proportional to the current (until you go much above the rated current and the rotor saturates). If the nearest current setting to the current in series is greater than the parallel setting then it may not make much difference. Karl has the motors on 2.37A, and the rating is 2.1A so it's already 13% over. The PM542 maximum is 4.2A, so the same as the motors ... so if putting in parallel gains less than 13% then you may not gain anything though it would be nicer. There's more to it than that though... in the end it's easiest to just try it and see. Keep an eye on the motor temperature too.

Quote:

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Originally Posted by Jonathan

You and Steve are both running these motors in Bipolar series, not parallel ... interesting.

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If so then it's very likely your way under voltage and just simply running out of torque, the torque drops off very quickly when wired series.!#

Quote:

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Originally Posted by JAZZCNC

If so then it's very likely your way under voltage and just simply running out of torque, the torque drops off very quickly when wired series.!#

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However, for completeness, the torque when wired in bipolar series is greater at low speed than the same motor wired in parallel.

It looks like in Steve's case it's the Y/Z axis motors that are in series, and they're not at fault. Still worth trying, as long as the power supply can take it.

Quote:

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Originally Posted by Jonathan

However, for completeness, the torque when wired in bipolar series is greater at low speed than the same motor wired in parallel.

It looks like in Steve's case it's the Y/Z axis motors that are in series, and they're not at fault. Still worth trying, as long as the power supply can take it.

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Yep exactly, thou as the speed rises the torque drops away very quick in series and because the X axis needs the most torque due to it's mass and it's happening when rapiding I'd be changing to parallel.

Edit: That said I still don't think this is Steves problem due to him having the problem at lower speeds.?????

Just taken some motor current measurements on my machine - measured at the output of the star-wired PSU:

- Powered up but stationary the 3 drivers and motors together pull 0.87A (DC) total. Motors bipolar series. Driver PM542 settings now 2A (RMS) limited.
- MACH3 jogging X,Y or Z axis individually pulls 1.36A during acceleration levelling at 1.25A - this is the machine's full MACH3 limited speed of 400mm/min.

Jogging in, say, X and then also jogging Y - ie causing the horrible mechanical noises and poor movement - pulls 1.6A to 1.9A total.

Jogging the Z full speed and then - at the same time - jogging either the X or Y in any direction does not cause any problem (likewise moving either X or Y and then engaging Z causes no problem).

My PSU is rated at (43V) 5+ amps so, given the figures above, current does not seemed to be an issue.

I'm wondering if this problem is due to inertia/momentum/twisting forces in the, not very expensive, X-Y table?

Hi Jazz..

Just a quick mention that I am only getting this problem when the X and y are at maximum speed...

Steve..

Have now re-installed Mach - no difference..
Also tried another PC, although it is a pretty low spec laptop (setup as a standard PC) - no difference..
Going to rewire my nema 23's (3Nm) in bipolar parallel today, not sure if I will be able to do the same with my Nema 34's as they are 4 wire motors, just waiting on a bit of advice on that, unless someone out there knows how to do it?

Just want to say that although I have not got to the bottom of this problem yet (and neither has Karl, my sympathies dude), I am very grateful for all the advice given.. Checking so many aspects of my machine is a real confidence booster with the level of scrutiny it has had this week, I feel like several engineers have checked my work and so far, most of what I have done seems right and a couple of things I have been able to improve..

Steve..

you cant connect a 4 wire motor in parallel, it is similar performance wise as if you had an 8 wire motor connected in parallel.
Out of interest does this problem happen if you disconnect the ballnuts from their mounts?
Also does the X axis stall when the Y axis is in a specific position or is it random?
My thinking is that is may be a mechanical problem with the stiffness of your machine?

Still happens with the ballnuts disconnected, I had removed the ballnuts last week and cleaned them out, then tested that principle as I was originally thinking along the same lines.. The problem can happen at any position on the bed (2mt x 1.4mt) although it seems to happen much more on moving the x axis +, rather than -..
Mechanically, the machine is sound and I have torn apart and rebuilt it twice in the last week, everything is freely moving..

If I get a chance, I will make a little video of it happening later today..

Steve..