MechMate CNC Router Forum

Go Back   MechMate CNC Router Forum > After Building the Beast - Operating , Troubleshooting and Maintenance > Troubleshooting
Register Options Profile Last 1 | 3 | 7 Days Search Today's Posts Mark Forums Read

Reply
 
Thread Tools
  #1  
Old Wed 20 January 2010, 12:57
Claudiu
Just call me: Claus #43
 
Arad
Romania
Loosing Steps - underpowered ?

I did cut some stuff for testing and learning. What I remarked after proper zeroing Machine Cords and proper zeroing starting point is that after the cut is done, lets say a full sheet of different shapes, when the spindle goes back to the starting point I see a difference of 1,4 on the table and on the screen ?
Why is that so, shouldn`t it go back to 0,0,0???
Next is that when the gantry is mooving fast over x direction I hear a crrrrccrrrr sound, gantry is not mooving and when it stops I realize that during all the sound that I heard the motors were active but did not turn. I checked rails, they had no obstruction. Pinions are well fitted on motor, screws are tight.
It`s strange that both motors are doing this simultaniously, my gantry remains ok, it`s not pulled on one side more or less...!
The only thing that I forgot about was the current resistor on the geckos, was still set to 1,5 Ah. Now I changed the resistors to 4 Ah and hope that this will change the behaviour of the twoo motors.
Can it be that underpowering or limiting current to the motors result in keeping them in a state of brrrrr but not turning?
Reply With Quote
  #2  
Old Wed 20 January 2010, 13:03
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
"I see a difference of 1,4 on the table and on the screen ?"

If the screen always corresponds to the position on the table then you have NOT lost steps.

"Next is that when the gantry is mooving fast over x direction I hear a crrrrccrrrr sound, gantry is not mooving and when it stops I realize that during all the sound that I heard the motors were active but did not turn. I checked rails, they had no obstruction. Pinions are well fitted on motor, screws are tight.
It`s strange that both motors are doing this simultaniously, my gantry remains ok, it`s not pulled on one side more or less...!"

. . . .now THAT is the classic lost steps due to too low current or too low voltage supply to the motor. (Or motors that are too small or incorrectly geared)

Watch the motor temperatures after changing the resistors.
Reply With Quote
  #3  
Old Wed 20 January 2010, 13:18
Claudiu
Just call me: Claus #43
 
Arad
Romania
I use the geared OM 7:1. I will check temps when cutting next time.
Thanks Gerald
Reply With Quote
  #4  
Old Tue 16 February 2010, 01:22
Claudiu
Just call me: Claus #43
 
Arad
Romania
Hi all,
I`m back with some new info on my loosing steps problem.
After changing voltage limitation from the geckoes to 4Ah, loosing steps got better. Temperature of the motors, when doing some surfacing along x axis raises to about 50 degrees celsius, but I was doing surfacing with some 18 mm tool so they had to run a lot.
But it`s not gone...
I`ve tried to do some other exclusions to find out where the problem could be.
1.st I`ve gone into WinXp and cut down more of it`s services wcich I will never use on the Mach comp. I stopped touching the computer during cutting something.
2.nd found out that I had to redo some earthing on my exhaust tube because I once in a while get a shot when touching table with my pants.( It`s a tiny shot like 1/10 of the power you sense when touching an electric lighter). It seems i still get some static from that evac system.
3.rd I`ve checked also the rails for mechanical defects, but they are all ok. Also loosing step does not appear allways in the same spot.

What is going on with the machine:
It is only one motor which causes the lagging ( lost step), the one oposite to 0,0,0 on the x axis. Mostly it appears when going fast from x-max to the 0 direction, and only into that direction. This is also the motor with the biggest backlash. I found out that the motor axis holding the gear is not 100% vertical on the rail, I have a dif of about 3 degrees. ( could this provoke jumping one tooth?)

When lost step appears it`s allways something like 1,5 to 2 mm, so it`s not only one but a whole bunch of steps...

I will check now my screening again inside the control box to be sure there is no emi inside near the bob where the output to the gecko starts.
Reply With Quote
  #5  
Old Tue 16 February 2010, 06:50
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
Claus-

I suspect the motor/pinion are binding to the rack somehow, increasing friction to the point that the motor stalls briefly. Since the other X motor keeps going, the gantry twists out of square, which somehow frees the binding enough to continue.

I'd try either tightening or loosening the slot and/or pivot bolt for that motor mount plate to see if it changes the behavior. From what you describe, sounds like it's a bit tight as a guess.

Tooth jumping should be a dramatic event that you would notice, so I think you're dealing with something else.
Reply With Quote
  #6  
Old Tue 16 February 2010, 07:15
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Claus, something else you can try is to swop motors, or geckodrives, with your y-axis and see if the problem moves to a different place.
Reply With Quote
  #7  
Old Tue 16 February 2010, 07:19
gixi
Just call me: Marius (AVO) #32
 
Bucharest
Romania
Send a message via Yahoo to gixi
Claudiu you should check if the motor pinion is not to tight to the rails. I had this problem when put back a motor on X axis and I forced the motor pinion to stay extra tight to the rail (it was the A motor). The only tension should be aplied to that pinion is the tension given by the spring.
Reply With Quote
  #8  
Old Tue 16 February 2010, 09:14
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Claus,

Did you grease your racks? After you do what Gerald suggested.
Reply With Quote
  #9  
Old Wed 17 February 2010, 08:57
Claudiu
Just call me: Claus #43
 
Arad
Romania
Hello and thank you all for the feedback,

What Ive done so far and some results:
I checked rails for mechanical defects, they seem ok.
I rearranged motor plate so pinion is vertical on the rail.
I recentered pinion to slide evenly along the rail.
I greased rails and pinion with an anti seize lubricant.(thanks Nils)
I loosened the spring, and rechecked skrews holding motor plate in place.(thanks Brad) Theyre easily moveable now. (thanks Marius)
I set back Mach frequency to 25kHz.
I tuned motors again from geckoes.
I reduced Motor velocity to 5000 mm/min.
I changed acceleration Settings to 50.

Allways checking MM behaviour between each step did not bring any success until I changed:

Step pulse to 5
and Dir pulse to 5

I still have to read more about these settings but it seems that symptoms disappeared.

After that I started raising velocity again but got a stall in the motors above 9000 mm/min. Stall means I heard them brrrr but no moovement anymore, simultaniously on both x motors. I guess thats because of the frequency setting and motors came to their max rotation value.!?

I set now velocity to 8000 and accel. to 70. I will do some more testing also under working condition.
motor speed.jpg
Gerald, I thought about swapping motors, do you think it is enough to swap only the back side of the geared motor and leave the gearbox mounted on the machine or should I change the complete units?

Am I demanding too much speed? It is tehnically by the limit to go with 8000 mm/min?

I also post here some CV Settings. Maybe it helps.
CV setting.jpg

Last edited by Claudiu; Wed 17 February 2010 at 09:20..
Reply With Quote
  #10  
Old Wed 17 February 2010, 09:51
lumberjack_jeff
Just call me: Jeff #31
 
Montesano, WA
United States of America
I run EMC, but I have my acceleration set to something like 10inches / min / min.

The speed limit on my machine is comparable to yours and is a function of corner speed. Does the Mariss formula suggest that you should be getting higher speeds?
Reply With Quote
  #11  
Old Wed 17 February 2010, 09:57
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by Claudiu View Post
Gerald, I thought about swapping motors, do you think it is enough to swap only the back side of the geared motor and leave the gearbox mounted on the machine or should I change the complete units?
It is not a good idea to split open the OM gearboxes - I had some problems there once and the motor was jammed afterwards - no movement at all. After a few attempts, it suddenly was running again and I am still not sure what I did wrong.
Reply With Quote
  #12  
Old Wed 17 February 2010, 10:07
Claudiu
Just call me: Claus #43
 
Arad
Romania
ok, you convinced me. I change whole unit when nothing changes in behaviour.
Gerald, what do you think of the speed settings?
Reply With Quote
  #13  
Old Wed 17 February 2010, 10:27
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Claus, I am out of touch with the speed settings on the geared motors. (I have not "tuned" a MM for a few years). But 8000mm/min [320 inch/min] sounds a bit low.
Reply With Quote
  #14  
Old Wed 17 February 2010, 11:18
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
I have my OM 7.2s at 450 in/min, largely due to the limits of the PC I'm using. I went out and pushed the PC beyond it's reliable limit, and got 500 in/min. I recall running rapids at 600 in/min on a different PC in the past. There are no symptoms of motor problems at any of those speeds. So I would expect you to be able to get to 12000 to 15000 mm/min with those motors.
Reply With Quote
  #15  
Old Wed 17 February 2010, 11:39
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Have you looked at Typical settings for Mach motor tuning ? Looks like you are not far off the mark for speed, but that your Acceleration setting can be increased a lot. This will have a big effect on CV settings. (Your accel. is 70 while everyone else is around 500)
Reply With Quote
  #16  
Old Wed 17 February 2010, 14:48
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
What is your power supply's voltage? Remember that Current mostly impacts torque and Voltage mostly impacts speed. You stated that your motors were running about 50-C. That seems a little low to me. When I run my PK296B2A-SGxx motors with a 35VDC power supply, they temperature stabilize at about 65-C. (I try to keep motors below 80-C.)

The OM motors are derated because of the gearboxes. The identical PK296-03AA motor is rated at 4.5A when wired half-coil, but the geared motors are rated at 3A. Drawing less current will allow the motors to run cooler, so that may be the reason your motors run at 50-C.

Under test loads, I've run my motors at 900 RPM, which would be about 8-ips (or about 12,000 mm/minute) assuming a 1.25" diameter spur gear.
Reply With Quote
  #17  
Old Wed 17 February 2010, 15:10
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
Claus' build thread shows a 29 VAC toroidal, so about 40VDC, presumably. Claus can you confirm that is the measured amount?

Also, can you confirm the measured value of your current set resistors?
Reply With Quote
  #18  
Old Wed 17 February 2010, 18:54
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The current set resistors for a PK296A2A-SG7.2 motor and a G203v stepper driver should be 35k. I use the closest standard resistor, which is 33k, on the motors at my test bench.

The formula is: 47 * Amps / (7 - Amps) = Current Set Resistor X 1,000. Example: 47 * 3A / (7 - 3A) = 35.25 and 35.25 X 1,000 = 35k. A 1/4 watt resistor works fine.
Reply With Quote
  #19  
Old Thu 18 February 2010, 03:34
Claudiu
Just call me: Claus #43
 
Arad
Romania
Quote:
Originally Posted by bradm View Post
Claus' build thread shows a 29 VAC toroidal, so about 40VDC, presumably. Claus can you confirm that is the measured amount?

Also, can you confirm the measured value of your current set resistors?
The sec value of the torroidal is 29 V measured, after the rectifier from PMDx its at 39 V. All measured.
The resistors on the geckoes have a measured value of 56 kOhm.
My motors are half coil. Would it be a good idea to swap coils, maybe theres something wrong with one of them?
Reply With Quote
  #20  
Old Thu 18 February 2010, 05:55
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
I looked at your 'build' section and noticed in the photo from the first page of the posts that you have JP1 on the PMDX-122 set to positions 1-2 (5V) instead of to positions 2-3 (ground). That would cause problems for the Geckodrive G203v. The G203v uses a common Ground signal and requires that the step and direction signals be Active High. (The G201 and G202 are just the opposite. They require +5 volts on the common and Active Low signals.) If JP1 is set to +5V, that might also explain why you get better results when you set Step and Direction to 5 in Mach3.

You may have changed that setting. I only scanned your build for photos of the PMDX-122.

Because I sometimes use G202 stepper drivers on my test bench and sometimes use G203vs or the G540, I have to constantly change the JP1 setting and the Mach3 pin settings. When I forget to change JP1, I get missed steps and rough running.
Reply With Quote
  #21  
Old Thu 18 February 2010, 07:28
Claudiu
Just call me: Claus #43
 
Arad
Romania
Mike, Im working on swapping motors like Gerald proposed. Im gonna change z with x2. x2 is the one making trouble.
I checked BOB.

DSC00186.JPG

The jump 1 was in the right place but I also checked my ports and pins settings and found out that Step and dir low active was checked !!! Can this be a source of problems?
I unchecked them now and will test after swapping motors. Thanks
Reply With Quote
  #22  
Old Thu 18 February 2010, 07:34
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Claus,

I was accussed of changing too many things. When you are testing you need to change one thing and then test it. If you change two things like swapping the motors and unchecking dir low active, you don't know which one fixed the problem. Change one thing at a time, test. If it is still not working, put what you changed back and try the other thing. It some times will take multiple things changed but you don't know what your changes are doing if you change multiple things at the same time.

It takes time to fiqure out what the problem is and it takes consistant testing to do it.
Reply With Quote
  #23  
Old Thu 18 February 2010, 07:42
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Claus, you have told us that both your X motors give a similar performance now - there is no need to swop motors for more troubleshooting. Work with Mike Richards on your voltages, currents and settings.
Reply With Quote
  #24  
Old Thu 18 February 2010, 08:54
Claudiu
Just call me: Claus #43
 
Arad
Romania
Nils, you are perfectly right. In my list of the things I have done there was allways a checking and jogging to see if the simptoms dissappear.
Unfortunately it seems not to matter if I go fast or slow velocity, nor acceleration, nor direction.
You can hear only something like a clonk and thats all, gantry is out of square by some mm. There is no rule when it happens.

Gerald, the simptoms were remarkable on one motor. X2, the one far away from 0,0,0. After I set step and dir pulse to 5 it only seemed to be better ( in my hopes) but still I have those small blackouts. (not me, ...the motor)
Reply With Quote
  #25  
Old Thu 18 February 2010, 14:53
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Claus, having the signals checked 'active low' in Mach3 will cause roughness. (I've had to scratch my head a few times when I've changed between the G202, which uses active low signals, and the G203 or G540 which uses active high signals. When I had the polarity upside down, the motors ran noisy and rough.)

Verify that all signals are properly set. Having one X-axis motor active low and the other active high will not only cause roughness, but it will cause your gantry to 'rack'.

From a technical point of view, the problem with defining the active level has to do with when the signal is seen by the software. Normally, an Active High signal is seen when the signal changes from Low to High and an Active Low signal is usually seen when the signal goes from High to Low. Because there can be a large amount of elapsed time between signals, having a signal 'trigger' on the wrong edge can mess things up.

When I have problems that are hard to trace, I work with one axis as a time. Write a G-code file that only exercises one axis at a time. Try various speeds. When that axis works properly, modify the G-code to exercise another axis. If the X-axis is faulty, you may have to drop the motors away from the rails. That will tell you immediately whether the problem is mechanical or something to do with Mach3 and the steppers. But it's harder to trace problems when two motors are involved. In fact, when I've had problems with a slaved motor, I dropped the motors so that they could run freely and then I exercised one motor as the X-axis motor, without a slave, and then I exercised the other motor as the A-axis motor, without a slave. (In that case each motor seemed to work perfectly by itself, but the two motors wouldn't work together. If I remember correctly, it turned out to be different acceleration settings for the two motors in Mach3.)

Step by step. It takes time, but when you follow a systematic approach you can cross off the list everything that works properly until you find the problem.
Reply With Quote
Reply

Register Options Profile Last 1 | 3 | 7 Days Search Today's Posts Mark Forums Read

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Motors loosing steps - Breakout board not suitable mgandy02 Troubleshooting 17 Mon 02 November 2009 11:01
All motors run fine then start chattering and loosing steps - interrupt in the PC KevinL Troubleshooting 24 Wed 14 October 2009 22:11
Loosing steps - noise interference problems MariusL Troubleshooting 14 Sun 15 March 2009 06:34
Steps getting lost - poor quality parallel port cable javeria Troubleshooting 5 Wed 03 December 2008 07:35
My introduction - the first scary steps - Miami Florida thesaent14 Introduce yourself and start planning 11 Sun 16 September 2007 14:01


All times are GMT -6. The time now is 13:14.


Powered by vBulletin® Version 3.8.3
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.