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 Fri 26 December 2008, 08:09
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Shudder along X Axis - unresolved

I would like to address my problem with the X axis and see if I can find a solution.

At acceleration of 25, 10 and 5, I can feel a shudder in the gantry and hear it when I move back and forth along the X axis. This is an X axis problem. It is more pronounced when the gantry is moving at a faster speed but even at slower speeds you can hear and feel it. The velocity is set at 250.

I have all motors tuned.

I tried slightly loosening the two bolts that hold the motor plate to see if that would make a difference but it did not.

I have tired putting less tension on the springs but that did not help.

The Gantry moves smoothly along the X axis when the X motors are loose and the gears are not engaged.

I am starting to think that the V Wheels are the problem. Sean thinks it might be the rack and gears not messing correctly but that are his thoughts over the phone. He has not looked at the problem.

I am open to suggestions of things to try.
Reply With Quote
  #2  
Old Fri 26 December 2008, 09:21
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Did you say previously that you had disengaged one X motor from its rack at a time, and that even with a single motor (either one) the shudder remained the same?

Does it matter where the Y-car is parked along the gantry when you get this shudder . . . . on either motor?

I think you also said before that the shudder is more pronounced at certain positions along the X-axis?
Reply With Quote
  #3  
Old Fri 26 December 2008, 09:30
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Gerald,

1) Yes the shudder remains the same when either motor is disengaged.

2) It doesn't matter where the Y car is located.

3) It appears there are locations were it appears more pronouced.
Reply With Quote
  #4  
Old Fri 26 December 2008, 09:40
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Did your adhesive tape bond properly between the rack and the alu?

With both x-motors disengaged from the racks, do all 4 V-Rollers of the gantry seat down firmly? Along the whole length of the x-axis?

Could you plug an X motor cable onto the Y-Gecko and confirm that the shudder remains? This will tell us we are talking mechanical and not electrical/tuning issues.

Is it not perhaps a rattle instead of a shudder - maybe something like the y-cable chain rattling on the back of the gantry?
Reply With Quote
  #5  
Old Fri 26 December 2008, 09:54
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Gerald,

1) The rack is firmly connected to the Aluminum.

2) I will have to check that but I have checked in the past and the wheels appear to be set.

3) I can not plug a X into a Y with out making up a new cable.

4) It is not a rattle. If I lightly place my hand on the Gantry while it is moving, I can feel vibrations in the Gantry. This is not some wires rattling around.
Reply With Quote
  #6  
Old Fri 26 December 2008, 10:10
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Even with the mass of steel we have there, feeling some vibration is normal. Sitting in my office downstairs of my son's MM, I could hear an irritating vibration coming through the concrete slab (until it got rubber shoes).

However, your level of vibration may be excessive and it is going to be hard to diagnose from this side of the Altlantic.

If I were you, I'd look at the cut quality produced by the various axes. ie. see if a square has better y-sides than x-sides. I have a funny feeling your shudder/vibration is quite normal. Probably caused by the springloaded teeth of the pinions riding on the tips of the rack. The x-racks are more solidly mounted, particularly directly over the legs. The y-rack is on a slightly spring gantry......
Reply With Quote
  #7  
Old Fri 26 December 2008, 10:17
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Gerald,

I am only getting the vibration on the X axis and It might be normal but Sean noticed when he was here and had me slow the machine done but it still exist. I am hoping that Sean will be able to help me look at it but I was going to see if I could find a solution before that.

Most of what I have been cutting has been close to the 0,0 as I learn to use the software. I am concerned that the vibration will affect the quality of my cuts.

Thanks for the suggestions.
Reply With Quote
  #8  
Old Fri 26 December 2008, 13:20
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
You say you can hear it, right? Could you manage to post an audio file? Just a crazy thought.
Reply With Quote
  #9  
Old Fri 26 December 2008, 15:01
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
I will put an audio file together and see if I can post it.
Reply With Quote
  #10  
Old Fri 26 December 2008, 15:36
William McGuire
Just call me: Bill
 
Weiser, Idaho
United States of America
May be a little of the current problem, but when tuning the motors, what would one due if one of the X axis motors tuned differently from the other? Would you just balance them out so they are not too far out?

Anything else would cause some strain in both motors wouldn't it?

Bill
Reply With Quote
  #11  
Old Fri 26 December 2008, 16:17
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Bill

When you tune the motors, you are twiking the Gecko drives so that each motor is running as smooth as it can. You remove the spings and allow the motors to drop from the rack.
Reply With Quote
  #12  
Old Fri 26 December 2008, 22:03
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Bill, the tuning is to minimise the natural resonance of a motor. This resonance is in a rather narrow speed range and causes vibration when the motor is turning near that speed.

The motor's natural resonance is caused by the way it is constructed; wire size used in coils, coil density, etc. Which means that a family of motors from the same same supplier, with the same model/type number, will have the same resonance point. And the Gecko's will be tuned to the same point. After tuning the Gecko's, you can happily swop motors around without worrying about tuning again.
Reply With Quote
  #13  
Old Sat 27 December 2008, 06:50
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Gerald,

I slowed the motors way down 10 - 1 and I can still feel and hear the shudder. I place my hand on the motors and I can feel but I can not determine if the problem is the racks or the wheels.

Though I lubricated the racks, I am going to buy some Dupon teflon and then I will try again.

I did record but with the motor sound it is hard to hear at the slower speeds.
Reply With Quote
  #14  
Old Sat 27 December 2008, 07:10
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
I get the impression that the shudder is not changing its frequency (or pitch, or tone) and that it only changes its amplitude (or loudness, or volume) when you change the motor speeds. Is that right?
Reply With Quote
  #15  
Old Sat 27 December 2008, 09:01
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Gerald,

Yes, I think that is correct.

I have placed my hand on the motor and even at lower speeds I can feel some thing. At higher speeds it is more pronounced.

I would have included a zipped sound file but I need more space. Please add. We can delete after we are done.
Reply With Quote
  #16  
Old Sat 27 December 2008, 09:25
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
How much space do you need?
Reply With Quote
  #17  
Old Sat 27 December 2008, 09:28
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
Can you feel it on the motor when the motor is disengaged from the rack? How about if you put a little load on the motor with a gloved hand?
Did you not feel this during your kitchen table project?
Did you have to correct the X axis to get it to move the right distances, like perhaps by having to double the values?

Here's a crazy thesis: You've got the motor wires crossed, and so you're actually driving them across the two output phases of the gecko. Test: pull the wires at the gecko, and measure the resistance across the phase A pair, and across the phase B pair. You should get a complete circuit with a fairly low resistance, and the values should be about the same. If you get an open circuit, then you've got the cross condition. If you get differing values, something is funny with your motors.

Hm.. are these 4, 6 or 8 wire motors? Is it possible that you have one phase full coil, and one half coil?

Grasping at a few straws here ...
Reply With Quote
  #18  
Old Sat 27 December 2008, 09:42
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
I eceeds my quota by 1.38 MB. If that is too big I can make it smaller.
Reply With Quote
  #19  
Old Sat 27 December 2008, 10:45
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Brad,

Do you think there is some thing wrong with the motors?

The motors run fine when they are engaged with the rack. They are smooth.

I just can feel the vibration when I place my hand on the motors like the feel the vibration when I place my hand on the gantry.
Reply With Quote
  #20  
Old Sat 27 December 2008, 11:35
William McGuire
Just call me: Bill
 
Weiser, Idaho
United States of America
"Bill, the tuning is to minimise the natural resonance of a motor"

I was thinking of the motor tuning done during the Mach3 setup (config... motor tuning and setup).

If one were set up the 2nd X axis motor as a slave, wouldn't that be called the A axis in Maqh3?

If so, and the velocity or acceleration were different for the two motors, couldn't that cause a problem? Or more likely, am I just not comprehending the setup correctly?
Reply With Quote
  #21  
Old Sat 27 December 2008, 12:01
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
When you have two X axis motors on the MechMate, you have a separate Gecko for each Motor. Mach3 sends instructions for X to the PMDX 122 (in my case). The PMDX 122 sends the instructions to the Geckos which control the motors. The X instructions are the same. The X output on the PMDX has a set of wires for each Gecko so there are two sets from X. The Y output and the Z output have only one. When you tune the motors in Mach3, you are telling Mach 3 the Velocity and Acceleration that you want for each Axis. So I tell Mach 3 that I want to use 250 - 10 for X, it will use the same values for both motors. Or actually they are Max values that will be used.

When you tune the Motors for the Geckos, you are tuning as Gerald explained.

To help others understand my problem. The motors have been Gecko tuned and I have configured them in Mach3.

I believe my problem is a rack or wheel problem and not a motor problem. The motors run smooth. It is possible there is no problem and I just think there is a problem. But I did not notice the same thing on Sean's machine.

Last edited by sailfl; Sat 27 December 2008 at 12:06..
Reply With Quote
  #22  
Old Sat 27 December 2008, 12:17
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
The hypothesis I was testing would have motors that ran rough or cogged only when they're under a little load.

I think from what I've read up above that your motors appear to run smooth when disengaged, but that your gantry rolls smoothly when the motors are disengaged. Changing the amount of spring tension on the motors had no effect. If it's a wheel problem, I'd think you'd be able to feel it by sitting on your gantry and rolling yourself around the table. Your weight would substitute for the pressure from the springs and motors.

Have you tested your motors disengaged, but under some load (like using a gloved hand to add a little bit of resistance to turning) ?
Reply With Quote
  #23  
Old Sat 27 December 2008, 13:06
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Brad

I have not tried adding a load to the motors with them disengaged from the rack. You are thinking that the motors might be okay with out a load but that they are having a problem with a load.

I have also not tried sitting on the gantry and moving it under a load.

I can try both of these things.

I have had another thought. If there was a load problem, the vibration would appear all the time but that does not happen. It is only in certain places along the X.

Last edited by sailfl; Sat 27 December 2008 at 13:09..
Reply With Quote
  #24  
Old Sat 27 December 2008, 13:27
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Back from dinner (10:26pm). . . . .

Nils, are your motors tightly screwed to their mounting plates? (Screws not too long, bottoming in holes?)

Are the mounting plates firmly held between the plastic washers?
Reply With Quote
  #25  
Old Sat 27 December 2008, 13:45
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Nils, mail me the sound file, I will host it and post a link to it.
Reply With Quote
  #26  
Old Sat 27 December 2008, 15:25
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Gerald,

You are suppose to be celebrating......

Yes, the screws and bolts are tight to secure the motors to the plates and plates to the machine.

I will send you the file.

Thanks for your help.
Reply With Quote
  #27  
Old Sat 27 December 2008, 18:15
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Nils,
I will try to come by tomorrow morning and see if I can diagnosis the issue.
I have list of mechanical things to check on.
I will call in the morning.
Sean
Reply With Quote
  #28  
Old Sat 27 December 2008, 21:35
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Sound file at:

http:/www.mechmate.com/DSCN1161.avi
Reply With Quote
  #29  
Old Sun 28 December 2008, 11:52
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Update.

Sean stopped by today to help me trouble shoot my shudder problem and he discovered a number of things.

1) Spring Bolt on the Motor Plate. I removed the bolt on the motor plate to limit any additional pull that might cause the gear to bind with the rack. We could tell some difference so I will leave it for now.

2) Rail alignment and VWheels. In one section towards the +121 X, the VWheel was riding on up on the rail. On that side of the Gantry the wheels do not have the same number of washers. We are not sure if the washers need additional adjusting or the rails need adjusting. It may be both. I have to do some measuring and checking. My first assesment is that I need to twick the rail first and then check the how the wheels are riding. That I will tackle on Monday.

3) Gecko Motor tuning. When I had checked the motors, I thought they were very smooth. Sean also things they are smooth. We attempted to adjust but the pots did not appear to have an affect. Before any one asks, Yes I am sure we had the right Gecko for the motor.... Duh.

I will give you an update after I have worked on the above items so more.

Thanks for all the suggestions and help.
Reply With Quote
  #30  
Old Sun 28 December 2008, 13:16
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Addendum:
The vibration appears to be purely mechanical, but a small amount of odd resonance/vibration happens on the 0,0 side of the table around x +100 to 121.
After we rule out all mechanical, then we will move to the electrical side to see if any isolation, ground issues or other is present.

All in all.....we are being really picky. The machine in present state cuts beautifully and smooth. All the issue's we are seeing haven't affected cut quality - yet.

More updates as we move forward.

Funny - I find Nils even pickier than me.....and that's saying a lot!

Peace
Sean
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


All times are GMT -6. The time now is 13:06.


Powered by vBulletin® Version 3.8.3
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.