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Author Topic: Spindle problem... slowly decreases RPM until stop.  (Read 4853 times)

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Spindle problem... slowly decreases RPM until stop.
« on: February 25, 2015, 01:07:13 PM »
I just added a PWM spindle to my machine (Mach3 > SmoothStepper USB > Gecko G540).  Now it runs, but with some very odd symptoms:

  • The spindle gets up to speed quickly (1sec?), but then slowly drops in speed... from 2500 RPM initially, down to <100, then stall, over the course of 2-3 minutes.
  • If I check voltage across Ground->Speed pins at the spindle, I can watch it correspondingly drop slowly from 5V down until it stops, in tiny increments.
  • Power cycling the spindle or Gecko G540 does not fix it.
  • Stopping and restarting the spindle from in Mach3 does not fix it.  In fact, if I stop the spindle, and restart it, it continues at whatever slow speed it was stopped at, and continues it's slow decline to stall.
  • Changing the spindle acceleration in Motor Tuning of Mach3 has dramatic effects.  A setting of 1 gives the "slow decline" behavior above.  A setting of 5 causes the spindle to start, then stop within about 1-2 seconds.  A setting of 10 causes the spindle to start accelerating and then decelerate to a stop before it even reaches full speed (<1sec), then it will do the same thing when the spindle is stopped in Mach3.
  • Closing, and restarting Mach3, without turning off or resetting anything else, will reset the problem... resetting the spindle to its full speed, to start a new slow decline.
  • Also, not sure if this is  important, but I'm typing 2500 into the spindle box, Mach3 is showing 2500 in the sVo box, but the RPM box always shows less (~2415).

I'm thinking that since the problem persists until Mach3 is reloaded means the problem is likely in there somewhere.  Anyone have any ideas?
Re: Spindle problem... slowly decreases RPM until stop.
« Reply #1 on: February 25, 2015, 07:56:11 PM »
Vfd settings?
Re: Spindle problem... slowly decreases RPM until stop.
« Reply #2 on: February 25, 2015, 08:11:23 PM »
Sounds like the VFD speed reference input is setup for 4-20ma instead of 0-10Vdc.  Reading voltage of 5Vdc to ground is typical of 4-20ma... (1-5Vdc across the drive's internal 250 ohm resistor = 4-20ma). Typically there is a jumper on the VFD that has to be moved and then the VFD's speed reference input has to be programmed for 0-10Vdc so the rpm scaling is correct.
« Last Edit: February 25, 2015, 08:21:23 PM by geh7552 »
Re: Spindle problem... slowly decreases RPM until stop.
« Reply #3 on: February 25, 2015, 08:21:57 PM »
Vfd settings?

They aren't really set to much.  I enabled the spindle PWM, and set it to 50Hz in Mach3, and then enabled the spindle and set it to 50Hz in the SmoothStepper (USB) Mach3 plugin.  The spindle's motor tuning settings are currently set to 5000 steps, 60, 1 accel... no real reason why, except playing with it from the 1000/60/1 settings I've seen recommended elsewhere.

Sounds like the VFD speed reference input is setup for 4-20ma instead of 0-10Vdc.

Is this a setting in software or a physical switch somewhere?
Re: Spindle problem... slowly decreases RPM until stop.
« Reply #4 on: February 25, 2015, 08:25:31 PM »
Both are VFD specific... should be in the VFD user manual. The drive parameters have to be setup correctly. THEN the setting in Mach 3 have to be setup correctly. Just playing with the Mach setting alone will not fix the VFD problems.
« Last Edit: February 25, 2015, 08:32:17 PM by geh7552 »
Re: Spindle problem... slowly decreases RPM until stop.
« Reply #5 on: February 25, 2015, 08:56:46 PM »
Unless I'm misunderstanding what I have (not impossible, though maybe unlikely) I'm guess that isn't it then.

This is the spindle controller... http://littlemachineshop.com/products/product_view.php?ProductID=4213&category=

The instructions ( http://littlemachineshop.com/instructions/4213CNCSpindleControlUpgradeKit.pdf ) include a wiring diagram to the G540 (page 8 ), and I have it set up as described.  There are no jumpers, DIP switches, or other adjustments on the board (besides a potentiometer for speed adjustment, which I've tried in many positions with no change in effect, besides top speed).  I know what they say about assumptions, but I'm taking this to be an indirect confirmation that it's known to work with the G540.
Re: Spindle problem... slowly decreases RPM until stop.
« Reply #6 on: February 26, 2015, 11:07:58 AM »
Contact the seller and ask for help. The wiring diagram shows a AC motor and connection but it's labeled as a DC motor?? The specs also state DC brushless motor control?? Which is it AC or DC?

Good Luck...
« Last Edit: February 26, 2015, 11:18:33 AM by geh7552 »
Re: Spindle problem... slowly decreases RPM until stop.
« Reply #7 on: February 26, 2015, 12:33:44 PM »
Is there a reason you think it would be on the spindle or spindle controller side of things?  If I wire the spindle controller up manually (e.g. just jumpered, not connected to G540) it runs fine.  The speed voltage signal from the G540 drops slowly over time, and since it resets happily when Mach3 is restarted it seems logical that the "issue" would exist in Mach3 or the SmoothStepper plugin for Mach3.  Do you disagree?  Why?
Re: Spindle problem... slowly decreases RPM until stop.
« Reply #8 on: February 26, 2015, 01:01:49 PM »
The seller has a 800 number to call.... best bet is contact them for help. One issue I see (and it may not be an issue) is the controller is 0-5Vdc where as Mach 3, ESS and Gecko 540 are all 0-10Vdc speed references. Could be a scaling issue. What I read is this is for a DC brushless motor??   
Re: Spindle problem... slowly decreases RPM until stop.
« Reply #9 on: February 26, 2015, 04:45:33 PM »
I really can't understand how it would be the spindle, since the spindle runs perfectly if manually connected (not to the G540).  I called them anyways... and they had nothing to offer.  They said if it works when wired up manually ("simple connections" in the manual), then their side of things works... which sounds reasonable.

I understand what you're saying about 10V vs 5V, but then it should run at 1/2 speed at least.

I'm waiting to hear back from SmoothStepper support too.
« Last Edit: February 26, 2015, 04:49:11 PM by guido666 »