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  1. #11
    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.?

  2. #12
    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..

  3. #13
    Quote Originally Posted by fasteddy View Post
    By ground, you mean earth right? Connect 0v and or ground to earth?
    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.

  4. 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.

  5. #15
    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..

  6. #16
    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..

  7. #17
    Quote Originally Posted by fasteddy View Post
    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...
    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?

  8. #18
    Quote Originally Posted by fasteddy View Post
    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..
    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...

  9. #19
    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..

  10. #20
    Quote Originally Posted by fasteddy View Post
    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..


    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.

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