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

**Jonathan** · 04-10-2011

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..

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...

**fasteddy** · 04-10-2011

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..

**Jonathan** · 04-10-2011

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...

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?

**fasteddy** · 04-10-2011

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..

**Jonathan** · 04-10-2011

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..

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.

**fasteddy** · 04-10-2011

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..

**fasteddy** · 04-10-2011

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...

**audioandy** · 04-10-2011

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

**Jonathan** · 04-10-2011

Originally Posted by audioandy

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

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...