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  #1  
Old Mon 02 February 2009, 18:07
waynec
Just call me: Wayne from White Salmon
 
White Salmon, WA
United States of America
Lurching at Reset - interference from spindle VFD

Boy, I just spent a half a day messin this contraption. I'm about ready to throw it over a cliff. For the record its NOT a MechMate. I wish it was.

Anyway, that's all working now and seems to be OK except for a little problem. My problem is that when I push the RESET button in Mach 3 to take it offline I get a good 20mm of lurching motion on the X axis motors.

It doesn't show on the Mach 3 DROs, so I dont think that Mach is sending step signals. It seems lke the motors are getting a surge at shutoff. I wonder if I'm missing some setting, or if something is wired goofy.

Thanks as always for the excellent help here.

Wayne from White Salmon
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  #2  
Old Mon 02 February 2009, 23:36
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
". . . I push the RESET button in Mach 3 to take it offline"

1. Are you using the mouse to click the Reset on the screen, or

2. Are you using keyboard keys (forgotten which they are), or

3. Do you have a wired-in Reset button away from your PC?

What do you mean by taking it "offline"? (Reset and offline mean different things to me - they are not the same)
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  #3  
Old Tue 03 February 2009, 13:10
javeria
Just call me: Irfan #33
 
Bangalore
India
Wayne - when this happens is your VFD on or off -

http://www.cnczone.com/forums/showth...t=6840&page=33

mike at the zone had a similar problems - but it was a servo -

just hinting - the problem might be anything else!

RGDS
Irfan
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  #4  
Old Tue 03 February 2009, 22:57
Kobus_Joubert
Just call me: Kobus #6
 
Riversdale Western Cape
South Africa
Send a message via Yahoo to Kobus_Joubert Send a message via Skype™ to Kobus_Joubert
I could be on the wrong track, but this sounds like too high a acceleration speed setup in Mach. I had something similar when I first started....this beast will take off....run like the wind and when I release the keyboard button while jogging manually the gantry kept going....brought down the acceleration and it stops dead when I take my finger off the keyboard.
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  #5  
Old Wed 04 February 2009, 03:10
waynec
Just call me: Wayne from White Salmon
 
White Salmon, WA
United States of America
Thanks for the great replies.
Gerald, I use the mouse to click the reset button on the Mach 3 screen. Offline means just clicking the reset button so that the motors are no longer controlled by Mach 3, or at least I can't jog or move the motors after reset is clicked.

The VFD is generally ON when this happens- but I'll double check this excellent tip when I work on it tomorrow. If its related to this new set of gear, shutting the spindle may remove the problem. Thanks, Javeria for a great tip that will help me narrow things down.

Kobus, I'll try changing acceleration tomorrow, and see if its related. That is also an easy way to see if its related to software somehow.

I found the problem that was causing hair loss a couple of days ago. Its another broken wire- two actually. The wires have always broken right at the metal connectors on the back of the plugs. They are Molex connectors, and I'm developing a true distaste for them. I can get the wires into them OK, but for some reason the connections are getting stressed and the wire is breaking right at the connection point. This last one was hanging on by one thread, and when I moved the control box it finally broke. I also had a loose connector at the Gecko. Both easy enough to fix. Tomorrow I'll cut like the wind to try and catch up, and see if this happens any more.

But I'm considering swapping to a soldered connector with a screw on connection and proper strain relief, like military spec circular connections. I don't think these molex are up to the job. I'm a fair solderer, so for the price of a few chasis mount connectors and plugs I can greatly reduce the chance of intermittent wire failures. Seems worth it right now.

THANKS guys for your help. I'll test some tomorrow and see if I can narrow things down.

Wayne
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  #6  
Old Wed 04 February 2009, 05:55
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
If it odd movement after a mouse click, then it might be worthwhile trying another mouse and keyboard. We had some odd things happening where a new keyboard and mouse cured the problem. Still don't understand it, but it made a difference.

Yeah, connectors are the devil . . . .
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  #7  
Old Wed 04 February 2009, 12:13
waynec
Just call me: Wayne from White Salmon
 
White Salmon, WA
United States of America
HA! Thanks Irfan for the tip. I turned the spindle VFD off before clicking on RESET, and it did not lurch at all. So that really narrows it down. Maybe I'll go over and ask at the CNC4PC blog and see if there's a history of this. Maybe one of the pieces of my spindle chain has some loop path so that when I disconnect a surge of current finds its way back to the Geckos or to the motors themselves.

I don't want to have to turn the VFD off every time I click reset, but if this is the only practical solution I can figure out a shut down routine.

Anyway, HI 5 to Irfan

W
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  #8  
Old Wed 04 February 2009, 12:54
javeria
Just call me: Irfan #33
 
Bangalore
India
wayne - straight away i can say that you have an issue of grounding -

is your spindle cable shielded? if so how is the shield connected?

if you go thru the CNC zone thread which Mike posted - there is everything there

May be our own electronics man (Mike)can comment here

RGDS
Irfan
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  #9  
Old Wed 04 February 2009, 19:53
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
Wayne, I think what Irfan means by "issue of grounding" is that you have an electrical noise problem, and I agree.

I'm hard pressed to think of any kind of "surge" that would cause stepper motors to move multiple steps (and the 20mm of lurch you are describing is a lot of steps!). However, it's easy to imagine noise on the 'step' input of your geckos causing motion. I'm not sure what's stopping the motion, though. Does your 'reset' button turn off the motor power supply? If so, then perhaps you're seeing the capacitor get drained, which ends the lurch.

Irfan is also correct that the usual solution to this class of problem is to clean up your shielding and grounding. If this has already been done, then you may need to add a pull-up, or pull-down resistor to the step signal to make it more resistant to noise. Let's fall off that bridge when we get to it, though.
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  #10  
Old Wed 04 February 2009, 20:21
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The mouse clickable "Reset" of Mach3 should NOT be turning off the power supply - this is why I a bit confused with Wayne saying it takes his motors "offline".

The Reset button flashes when a limit or E-stop has been hit, and Mach stops all movement. Clicking on the button allows Mach to move again. The button toggles - click on it under normal circumstances and it will flash while stopping movement - this is the mode Wayne refers to.

But I havn't seen anyone that has this button functioning as a true mouse-clickable E-stop where it shuts down the power in the control panel. I mean, the button is activated by limit switches, and that shouldn't be shutting down the control panel.
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  #11  
Old Thu 05 February 2009, 09:51
waynec
Just call me: Wayne from White Salmon
 
White Salmon, WA
United States of America
I read the thread at the Zone and I can't say I"m experiencing the same thing. My motors don't run away on me, they stop after a one time jerk. It doesn't sound like a motor running at all.

Really, when you suggest that its a capacitor emptying that sounds more like what I'm experiencing.

But I do have all my spindle control junk mounted inside my control box. By junk I mean the speed control board, a parallel port buffer with its USB power supply, and a parallel port breakout board that lets me connect to the speed control board. Can these be the source of noise?

I don't have a shielded cable to my spindle- just a hacked up extension cord. I'll install this if its needed, but I don't have any other problems with this, so if the noise source is more likely INSIDE the control box I'll build a shield to isolate the junk inside the control box.

Sigh. I was hoping to miss the hassle of chasing noise problems. But in the end it will make my router more reliable and help me pick up chicks.

Thanks for the help!

Wayne
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  #12  
Old Thu 05 February 2009, 14:54
Alan_c
Just call me: Alan (#11)
 
Cape Town (Western Cape)
South Africa
Send a message via Skype™ to Alan_c
Quote:
Originally Posted by Gerald D View Post
The mouse clickable "Reset" of Mach3 should NOT be turning off the power supply - this is why I a bit confused with Wayne saying it takes his motors "offline".

The Reset button flashes when a limit or E-stop has been hit, and Mach stops all movement. Clicking on the button allows Mach to move again. The button toggles - click on it under normal circumstances and it will flash while stopping movement - this is the mode Wayne refers to.

But I havn't seen anyone that has this button functioning as a true mouse-clickable E-stop where it shuts down the power in the control panel. I mean, the button is activated by limit switches, and that shouldn't be shutting down the control panel.

Mine works like that, as will anybody using the SoundlLogic BOB and CNCDirect BOB (or any bob that has relays controlled by the charge pump) I have wired the control signal to the main contactor through this relay, so if the computer faults, the supply to the geckos switches off. If I reset on the computer, I have to restart the geckos before I can move. It may prove to be inconvenient as any time that the charge pump triggers on the computer I do actually need to re-home the machine to maintain accuracy - but I feel it is a safer arrangement.
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  #13  
Old Thu 05 February 2009, 18:00
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
Thanks, Alan, I was wondering about that.

Wayne: By definition, the output of a VFD to a spindle is an electrically noisy signal with a variable frequency. Running it through an unshielded cable acts as an antenna to broadcast the noise in your shop area. Under ideal conditions, it's good to stop both the source antenna (that unshielded
cable to the spindle), and the receiving antenna (your wiring from BOB to geckos).

While you could concentrate just inside the box, you may want to consider the entire environment.

You don't happen to have an ordinary radio around, do you? I'm curious as to what happens to your reception when you turn your VFD on and off.

(For the record, the radio in my shop definitely picks up a little noise from my stepper motors, and they have shielded cables and use a heck of a lot less power than a spindle).

P.S. don't forget the tin foil hat to protect your brain
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