View Full Version : Heelp! Dual axis steppers.. Losing steps.. Pulling hair out..!

09-05-2010, 08:27 PM
Hi all..

Well, finally finished putting together my cheapo cnc router;
6' x 4' bed
4 x 3n stepper motors.. 2 are slaved together on the x-axis..
Chain drive X and Y axis
M20 x 3mm leadscrew Z-axis..
System 3 board with additional drv25 driver linked as added axis..
Mach 3 software..

Was chuffed to bits a few days ago when I configured Mach 3 to run it.. High speed jog worked really well, for a few minutes.. Then the X-axis (slaved the A axis to it in Mach 3) started 'jumping' and stalling about 5 or 6 times per revolution.. First on one motor, then occasionally on the other.. Then the direction would suddenly reverse on one motor and had to correct this in Mach 3..

I have now spent many hours trying to sort the, completely reconfigured Mach 3 several times.. Every time I switch on the motors and boards, it works very well for a couple of minutes, then starts dropping steps, occasionally one of the x-axis motors reverses direction.. The step dropping is much more pronounced when I run code and the x-axis is moving slowly..

Have got to the point of wanting to swap it for a playstation.. Might be more fun..lol

Any ideas please? Have rewired it several times, swapped around the drives on the boards, but it is only the slaved dual drive x-axis that is playing up.. Have spent hours skooshing around on the net, found many examples of folks having dual axis problems, but none that seem to echo my probs..

Could really do with some pointers as not much hair left to pull out now..!!


John S
09-05-2010, 08:37 PM
How have you got the motors wired/ series or parallel?

If they are Roys motors parallel requires 5 amps and series 2.5 but it will be right at the limit for a series 3 board.

Try going to series if you haven't and stuff a bloody big fan onto the board and try that.

John S.

09-05-2010, 09:20 PM
Hi John..

Have them wired in series and running at 2.5 amp.. Thats the way to get the most torque out of them yes? Have them stepping at 1/16th as the chain is a course pitch (1/2" pitch with 9 tooth drive spocket).. Tried them at 1/8th step but same problem..

Have the boards just out in the open at the moment, will put them in a nice box when everything is working.. As it was so cold in my workshop the last few days I did not think it would be a problem, but do you think they could be over heating? If that is a possibility I will box them with a nice fan before my next hair pulling session..

I was kinda thinking it might have been something in Mach 3 but the probs are a bit variable..


John S
09-05-2010, 09:47 PM
Steve, check your pulse setting in Mach.
go config > Motor Tuning and check the step pulse rate, try 5 or even up to 7

Gives it a longer pulse so the driver has chance to see it.

It's a funny setting as it's computer related, even if you are given an XML with it set at 5 your computer may see it at any figure, usually far lower than needed.


09-05-2010, 10:19 PM
Had similar problem on my machine when trying to run the motors too fast, they would work for a few minutes then started locking up and losing steps.

I did what John has suggested to you and put a bloody big fan cooling the driver cards (2 in fact), never had a problem since. Other than that you could try slowing the steppers down a bit.

09-05-2010, 10:33 PM
Thanks guys..

Will build a box with a fan tonight, fit it all tomorrow (Monday) and let you know how I get on.. Will also do as you suggest John..

Ta lots..! Might have some hair left by the end of the week..


13-05-2010, 11:16 AM

Sorted!! Running nice and smooth now.. Thanks Hiltonsteve, built a box like your with a couple of fans nicked out of a PC (courtesy of the local recycling centre).. Gonna cut some 2.5d stuff this afternoon.. Anyone have any 3D code I can use as a tester? Will try and produce some of my own this weekend but am a bit of a newbie to 3d so could take a while..

Thanks again..

14-05-2010, 09:23 AM
Hi again..

Finally!! It started doing it again.. It was the steps on the driver board, had it set to 1/8" step, once I got it down to 1/4" step it ran smoothly.. I guess my steam powered laptop (P3 600MHz) was not up to calculating so many steps.. Shame as the movement is not quite as smooth as I would like.. Better than a poke in the eye with a bent stick though..!


14-05-2010, 01:26 PM
Glad to hear that the fan idea worked but not so glad to hear about your problems re-appearing.

I would try and get my hands on an old pc to run it off rather than a laptop, heard about one or two people that have had problems using them and then other people having no issues at all, just pot luck into which category you fall.

If you lived a bit closer you could and come and 'borrowed' one of mine as I have a stack of half decent PC's in the corner of the workshop that would do a better job of running mach3 than your laptop.

14-05-2010, 02:32 PM
Ah.. What it is to be wealthy, well, in PC's that is.. Have built my CNC router for the princely sum of 400 all in.. Laptop was from freecycle so can't be sniffed at.. I did change the format of Windows 2000 from laptop mode to that of a desktop pc, bit fiddly as some of the drivers were not the same but it seems to work fine and does the job well enough for me at this stage..
If I can make a bob or 2 with it I will upgrade everything as I go along but am happy enough with it as I think I have a lot of learning to do what with software and all that..

Will post some pics when I have finished a bit of tweaking..
Thanks for all your help..!