View Full Version : slaved stepper problems

10-12-2011, 07:55 PM
i have two ballscrews, motors and drivers on my long axis, x and c. all of a sudden my c axis screw decides to turn the wrong way. if i move it posotive its fine and x and c both move posotive. if i move negative x axis moves negative and c moves posotive. i checked all the wiring it all seems fine and even changed to outputs on my bob to see if the bob is iffy. I just cant seem to find the cause as it has been running well for a couple of months now. any ideas anyone

10-12-2011, 09:57 PM
Sounds like the C-axis stepper driver direction input has stopped working as it's just stuck in one direction. If you can, measure the voltage at the direction pin of the C-axis stepper driver. If it doesn't change when you move the axis the other way then it's most likely a problem with the breakout board. If it does change then it looks like a problem with the driver. To check the driver try moving the input wires to a different driver and see if it works properly...

Have you got any spare outputs on the breakout board? If so you can use one of those for the direction input to C instead and just redefine it in the ports/pins settings. Probably easiest to try this first.

10-12-2011, 10:18 PM
alredy tried moving the wires on the bob and its the same so i'll try measuring the voltage tomorrow and post my results tomorrow. cheers jonathan

10-12-2011, 10:30 PM
measured voltage across the direction pin on all of the drivers. 2.99v one direction, 0v in the other direction so it can't be that. all seems to have happened just after i greased the ballnuts. any other suggestions

11-12-2011, 12:02 PM
What stepper driver is it? 2.99V might not be enough? What's the equivalent voltage for one of the drivers that is working.

For instance, if it's a M752 driver they have a 270 ohm resistor in series with the opto-isolator, which gives the correct current for those to switch on with 5V, not 3V ... 3V may not be sufficient.

Just re-read your post and noticed you said all the drivers, so that's all irrelevant! I'll leave it just in case it helps someone else.

It doesn't sound like a mechanical fault, as the motor isn't stalling it's just moving the wrong way? Have you tried putting a different driver on the C-axis? Swap Y and C for instance...if it works then you know it's not a mechanical fault and must be something wrong with the driver. I once had an optoisolator break on one of my drivers, connected it wrong, so I just soldered a new one in and it's fine.

11-12-2011, 12:15 PM
actually just came in from doing it. the driver obviously has problems. they are 452 drivers, all of them. any ideas what could be wrong with it.

11-12-2011, 12:22 PM
So just to be clear, the suspect driver works fine except for only going in one direction and the symptoms are the same if you feed it from the breakout board outputs that work with other drivers, and the motor/slaving works if you use a different driver for C?

Is the driver heating up abnormally?

Assuming the above is right, the driver is ignoring the direction input. That implies the opto-isolator inside is broken (so the PGA isn't getting the signal), or something else which will be more difficult to fix. If you want to post it to me I can have a look at it and hopefully fix it, just send me the return postage.

11-12-2011, 12:36 PM
just tring to get hold of bloke i bought them off to get replacement, refund seeing that they are less than 3 mnths ols. if not i will take you up on your offer. thanks a lot

11-12-2011, 01:32 PM
actually just came in from doing it. the driver obviously has problems. they are 452 drivers, all of them. any ideas what could be wrong with it.
If the voltage going to the direction is only 2.99V, it is unlikely a problemn with the driver but the signal is too low for the opto to change.
What are you using to power the 5V on the breakout board?
If you are using USB, dont and get yourself a 5V power supply.

11-12-2011, 01:57 PM
If the voltage going to the direction is only 2.99V, it is unlikely a problemn with the driver but the signal is too low for the opto to change.

3V is borderline, more susceptible to interference, (driver manual says minimum 7mA, 2.99V gets about 4-5mA) yes, but as the same signal works with the other drivers it's less likely to be that. Still it's worth just applying 5V and 0V to the direction pin from a power supply, or directly from the USB +5V to check.

11-12-2011, 03:31 PM
i'm using a routout cnc bob and 5v comes directly from the sreial cable. all the other three drivers are fine just not this one, although it was working for the last 2 1/2 months

11-12-2011, 03:35 PM
where are the opto isolators on the 2m542 drivers and what do they look like o i can see if its burnt or anything. cheers

11-12-2011, 03:43 PM
ok, my suggestion is to get a 5V power supply, connect this to the positive side of the pul+, DIR+ and ENA+.
Then the step goes to the PUL-, direction goes to DIR- and Enable goes to ENA-.
This bob is very simble and has no opto isolation of buffering and you are reliying of the quality of the 5V from the parallel port.
In most cases it will be under spec and 3V is borderling working or not, and any noise will give you problems.
you could also use the 5V from the USB, but i would not trust that, so getting a 5V power supply is much better.

11-12-2011, 03:49 PM
i actually meant the optoisolator in the driver itself. if it needs 5v then why do all the others work fine, by the way it might be my multi meter, might try on different setting to se if that changes anything

11-12-2011, 05:07 PM
tried on all settings, definately 3v

07-01-2012, 05:22 PM
I've now tested your driver. I connected it up in place of my Y-axis driver. I use *752 series drivers, so they're on 70 volts hence I used a lab PSU set to 48V for your driver. It works fine... I've not done anything to it, just connected it and changed the switches to 1600 step/rev as that's what I use. Then tested it on 800 and 400, not really expecting that to make a difference, and it didn't.

Interestingly the motor runs more quietly and possibly more smoothly (difficult to tell of course) with your driver. I'll have to test my own driver on 48V to see if it's just the lower voltage causing that. If not then that's useful information as it implies they use different control algorithms. As expected though the feedrate I can get with 48V is less (24000mm/min @ 2000mm/s/s acceleration) but still plenty!

So what would you like me to do now? Just send it back and hope it starts working on yours too? I'll have a look inside anyway just to be sure.

07-01-2012, 06:34 PM
yeah just post it back and i'll play with it again. were you running it from a 5v power supply o straight from the parralel port. when you get postage cost pm me and i'll paypal you the cost. thanks alot

07-01-2012, 08:12 PM
the motor will run quieter at a lower voltage, this is typical with stepper motors.
also you are running the 752 at 70V, this is the absolute maximum for this driver.
I would advise to run it at a lower voltage.
60V is a good voltage with the SY60.
As i mentioned before the problem is not with the driver but the 3V is too low.
I come across this a lot when people are using the parallel port.
It is a very cheap and simple 5 minute fix.

07-01-2012, 08:36 PM
I am running it directly from the parallel port.

the motor will run quieter at a lower voltage, this is typical with stepper motors.

I suspected that, was just interested in checking the theory!

also you are running the 752 at 70V, this is the absolute maximum for this driver.I would advise to run it at a lower voltage.

I would advise myself that too, however I've checked it by connecting my oscilloscope to the MOSFETs (IRF540) whilst running and measuring the peak voltages at the points where it they switch under various conditions. There are no peaks above the rating of the MOSFETs, which is 100V, so I'm happy that it's safe.
That's no reason for anyone else to do the same, since each system will vary.

It looks like it must be the low voltage of your parallel port, but that still doesn't explain why the driver wouldn't work from the same pins on the parallel port that the other drivers worked with.

07-01-2012, 09:30 PM
going over everything i think it has some thing ti do with the act that its slved with another motor/driver. the drivers on single axis are ine but this only happened on the slaved axis so maybe it was dropping the voltage too low

07-01-2012, 09:40 PM
Have you slaved it in mach3, so the drivers are connected to seperate pins (4 in total) of the parallel port, or is it one step/dir signal going to two drivers in parallel? If it's the latter that would explain it as the parallel port can't source much current, so with two drivers the voltage will drop.

08-01-2012, 08:54 AM
yes as jonathan has said, putting one output in parallel is not a good idea.
if it has its own output from the parallel port than it is just down to tollerance.
the driver that has the problems is just slighly out of spec or the others just have a higher tollerance.
just power the opto up with a good +5V and problem solved.
Or get a breakout board that buffers the outputs.

08-01-2012, 12:14 PM
yes it is slaved in mach3

11-07-2012, 07:00 PM
I know I'm late coming in with this but if you really must run the same axis on two stepper motors I'd be inclined to ensure they are identical bipolar type and connect them in series.