Messages

911

General Mach Discussion / Re: Problem in Mach3 R3.042.029?

« on: November 07, 2009, 09:24:50 PM »

"the stepper motors seemed to (obviously) be given the wrong signal at the time of the error" - Nothing obvious about it.  If the DROs indicate the correct position, but the tool is not where the DROs say it should be, you have almost certainly lost steps.  One more time, cut the velocity *and* acceleration in *half*, and see if the problem goes away.  What you are seeing is typical of a machine that is being commanded beyond it's capabilities.

Regards,
Ray L.

912

General Mach Discussion / Re: Problem in Mach3 R3.042.029?

« on: November 07, 2009, 06:39:15 PM »

"My controller is working perfectly - there are no skips when I jog manually." - That is not necessarily a true statement.  It is entirely possible, in fact quite common, for these machines to work perfectly when jogging, then screw up when machining.  There are many factors that can cause this, from noise and grounding issues, to power supply and controller problems.  Try detuning the motors - reduce velocity and acceleration by half or more - then re-run the program.  If the problem goes away, then there is a problem with the machine, not the software.  I'd guess you find it works fine detuned.

Regards,
Ray L.

913

General Mach Discussion / Re: Need help with resonance problem

« on: November 04, 2009, 10:20:17 PM »

This motor is German, Nanotec - Munich, 4H5618C0408, 3.4V, 2.85A, 1.8deg.  NEMA 23. 

 I'm not microstepping it.  The controller can do half and quarter steps if that will help.

The error is always the same direction.  I.e., when I stop it to check position, the carriage is always farther away from home than it should be.

In playing around with jog mode, I was able to run the stepper at 900 and acceleration of 120 without obvious stalling.  But in actual use I was still seeing errors down at 250 and 40. So I cut it to 25 and 2 and the errors stopped.

I'll generate some code to run it back and forth short distances, lots of reversals, for use in determining the velocity and acceleration at which the errors begin.  Given the mass of the leadscrew relative to the size of the stepper, I'm expecting that acceleration is going to be the problem.

Should I be half-stepping to improve performance?

Dave

You should definitely go to quarter stepping.

Regards,
Ray L.

914

General Mach Discussion / Re: Need help with resonance problem

« on: November 04, 2009, 06:20:10 PM »

You've verified that it behaves if BOTH velocity and acceleration are cranked way down, but doesn't sound like to verified WHICH one is the real problem.  In a stepper, resonance is more likely to cause a stall than a few lost steps.  Sounds to me like you're just seeing lost steps due to over-driving the the axis.  Leave acceleration very low, and see how high you can crank the speed and still get reliable results.  Once you find the limit, back off by 30-50%.  Now do the same with acceleration.

What stepper drivers are you using?  Are you microstepping?  If so, by what factor?  Any good stepper driver will have mid-band resonance correction,  but it sounds like your problem is occurring at higher speeds.  Microstepping will help mitigate high-speed resonance problems.  Mechanical dampers should rarely, if ever, be required in a properly setup system.

Regards,
Ray L.

915

General Mach Discussion / Re: one limit switch triggers two green input port pins

« on: November 03, 2009, 11:40:31 AM »

Try swapping the connections on the BOB for two switches.  You may have a short or bad chip on the BOB.  If you swap the wires and the double-LEDs move to another axis, then the BOB is defective.

Regards,
Ray L.

916

General Mach Discussion / Re: Switching on/off large DC Motor

« on: November 01, 2009, 03:45:58 PM »

You should also consider using either a DC motor controller that will ramp up the current, or switch in a series resistance for the first second or two, to limit the inrush current.  When first switched on, the motor looks like almost a dead short.  Those 40uF caps can provide an enormous amount of current for a short time - FAR in excess of the supplies continuous rating.  A smaller dedicated power supply with less capacitance would also help a LOT.

Regards,
Ray L.

917

General Mach Discussion / Re: G04 Dwell Code

« on: November 01, 2009, 01:09:01 AM »

I need to add a little extra time to my G code. I was trying to use G04 Dwell, G04 P3000 (I think this should give a 3 second dwell). When running this in Mach3, the dwell happens, but then doesn't resume the program. What did I do wrong?

The argument to G4 can be either milliseconds, or seconds, depending on a setting in Config->GeneralConfig.  Yours is obviously set to seconds.

Regards,
Ray L.

918

General Mach Discussion / Re: Unseen Post

« on: October 31, 2009, 02:03:07 PM »

Try making the post without the attachment.  If that works, then re-name the attachment, and edit the post to add it.

Regards,
Ray L.

919

General Mach Discussion / Re: Axis Drive Design Helper Spreadsheet

« on: October 28, 2009, 05:32:12 PM »

Ray, a couple questions, I'm not very familiar with excel, is it possible to make the "white" cells read only? It is easy to accidentally remove the formulas in those cells. Of course, if not saved, you can reopen the document to recover the lost formulas but it would be better if you couldn't erase the cells in the first place.

I like the "drop down" list. How do you make one? I couldn't find this function.

Steinar

Steinar,

I don't know of any way to protect individual cells, but I'm no expert either.

To create a drop-down, create the list of values you want to allow (they're at the bottom of column A in my spreadsheet), select the cell you want to have the drop-down, then select Data->Validation, and in the drop-down in the dialog that pops up, select "List", then put in the range of cells containing the allowable values.

Regards,
Ray L.

920

General Mach Discussion / Re: Axis Drive Design Helper Spreadsheet

« on: October 27, 2009, 04:17:42 PM »

Hi Ray,

very nice spreadsheet you have made

However there seems to be some errors still. Motor power at target feedrate both stepper and servo and thrust at target feedrate for servo. I'm working on correcting the formulas even if I'm not familiar with the new versions of excel.

Edit: This is for the metric version. I havent checked the Inch version.

You're right!  I fixed the max calculations, but not the target.  I'll get that fixed shortly.

Thanks!

Regards,
Ray L.