eshapeoko X and Y axes wobbling furiously!

roebotic
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eshapeoko X and Y axes wobbling furiously!

Post by roebotic » Fri Jul 12, 2013 12:01 pm

Hi,
I already posted about this problem in the discussion section and a couple of people got back to me with some helpful suggestions. I thought the problem was solved, which it seemed to be when I was just drawing straight lines. Originally the motors were making a really loud noise which they aren't any more. Basically when I get my machine to draw a small curved c kind of shape, the X carriage wobbles back and forth noticeably and also a little on the Y axis. It kind of sounds like a printer! I was instructed to check my steps per unit, which are fine and also the tightness of the v wheels which are also fine, possibly a tiny bit loose. The actual c shaped curve actually turns out fine every time, but I have yet to see a video of somebody's machine behaving like this, so i'm a little worried. I've tried varying the feed rate and the curve turns out good regardless of how fast i push the machine, it just wobbles a lot more.

I have a stock eshapeoko with dual Y drive. My Y carriages seem to be able to move out of alignment with each other slightly by up to a few mm. I think the only solution to this would be to upgrade the X axis and I don't know if this could be the cause of the wobbling?

I'm using mach3 in evaluation mode running on an old laptop, (with windows XP) that I have configured to try and run mach3 in realtime better, with a cheap Chinese breakout board. The electronics seem to be working fine, unless it could be a problem with the control signals, but I don't see how this could be making the machine wobble so much? I have the wantai 400 steps/rev, 56 oz.in motors. Any thoughts would be greatly appreciated.

WillAdams
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Re: eshapeoko X and Y axes wobbling furiously!

Post by WillAdams » Fri Jul 12, 2013 12:27 pm

Gantry racking has been an on-going problem w/ the default design --- I think dual X Makerslide should be the default --- it's a sea change in terms of rigidity for the machine. I also think that the bolt length for attaching things to the Makerslide holes should be much longer.

Not sure about how the dual motors play into this though --- I've been a big proponent of driveshafts instead of Dual Y motors, due to the complexities of the latter --- it may be that some aspect of homing them is complicating this, but someone more familiar w/ them will have to chime in on that.
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twforeman
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Re: eshapeoko X and Y axes wobbling furiously!

Post by twforeman » Fri Jul 12, 2013 1:17 pm

Check the belt tension. They should be pretty tight, you should be able to pluck them and have them sound the same on both sides of the Y axis.
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cvoinescu
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Re: eshapeoko X and Y axes wobbling furiously!

Post by cvoinescu » Fri Jul 12, 2013 1:20 pm

Can you make a video?

If the curve turns out fine in the end, I'm willing to bet that the laptop is underpowered for Mach 3, or too busy doing something else, so it just freezes momentarily -- but I can't really say without watching it. I have a suggestion: with little more investment than an Arduino Uno, you can run your drivers from GRBL, just to check that they work fine and it's not a mechanical problem (you also need some solid core wire, 18 AWG or 0.75..1.0 mm^2, which you can strip and plug directly into the Arduino headers). Any old laptop should be enough to send G-code to GRBL, even if busy defragmenting the drive, scanning the entire hard drive for viruses, applying two years worth of Windows updates, or whatever else it may be doing that's slowing it down. :)
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Re: eshapeoko X and Y axes wobbling furiously!

Post by cvoinescu » Fri Jul 12, 2013 1:49 pm

WillAdams wrote:Gantry racking has been an on-going problem w/ the default design --- I think dual X Makerslide should be the default --- it's a sea change in terms of rigidity for the machine. I also think that the bolt length for attaching things to the Makerslide holes should be much longer.
The bolts are 14 mm on the X and Y rails (where they go through 2 mm or 4 mm of material and a washer, so there's at least 9 mm into the MakerSlide), and 18 mm on the Z (where they go through 7.5 mm and a washer, so, again, just over 9 mm of thread bites into the rail). That's compared to 10 mm screws on the Shapeoko X and Y, and I think 14 mm on the Z. Do you think I should make them even longer?

Also, dual-X is a stock option -- it's not the default, but about three quarters of my customers chose it. Nobody ever bought a single-Y drive machine yet, but one person said they thought about buying the single-Y because they planned to use a driveshaft, but wanted the dual-Y motor parts anyway. Granted, because of the default X rail placement, it's not easy to do the driveshaft on the eShapeOko -- the shaft would go right through the spindle or the Z axis. The motor plates come with holes for alternate locations (one of which is the original Shapeoko position), so it can be done, but those arrangements can lose X travel (the spindle bumps into the front end plate, just like on the Shapeoko).
WillAdams wrote:Not sure about how the dual motors play into this though --- I've been a big proponent of driveshafts instead of Dual Y motors, due to the complexities of the latter --- it may be that some aspect of homing them is complicating this, but someone more familiar w/ them will have to chime in on that.
When the motors are engaged, with well tensioned belts (and you can really tension them on the eShapeOko, because the anchors are the end plates themselves on Y, and they're solid, 30 mm wide 2 mm thick stainless steel plates on X, with the belt only millimeters above the X rail), dual Y drive is incredibly solid. I'm pretty sure it's easier to move the gantry in the X direction, flexing the Y motor plates, than it is to move it in the Y direction against the engaged motors. Because the Y motor plates are so stiffly held, the X rail contributes almost nothing, so there's practically no difference between single-X and dual-X as far as resistance to racking goes. (Obviously, dual-X helps a lot with X carriage and Z axis rigidity in the YZ plane, so you want that.)
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roebotic
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Re: eshapeoko X and Y axes wobbling furiously!

Post by roebotic » Fri Jul 12, 2013 1:57 pm

Cheers guys i'll get on check over those issues and making video of it.

WillAdams
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Re: eshapeoko X and Y axes wobbling furiously!

Post by WillAdams » Fri Jul 12, 2013 2:22 pm

cvoinescu wrote:The bolts are 14 mm on the X and Y rails (where they go through 2 mm or 4 mm of material and a washer, so there's at least 9 mm into the MakerSlide), and 18 mm on the Z (where they go through 7.5 mm and a washer, so, again, just over 9 mm of thread bites into the rail). That's compared to 10 mm screws on the Shapeoko X and Y, and I think 14 mm on the Z. Do you think I should make them even longer?
I didn't realize (but should've guessed) that you'd made this change from the original design (which is what I was critiquing) --- hate to sound like a Pontiac commercial, but longer is better --- you've probably got the bolts long enough, but I'll confess that on my machine, I determined how deep a thread I could cut w/ my tap, tapped that deeply on all the holes, and then worked out using bolts long enough to almost bottom out for the X and Y connections for each position.

Interesting that the other mechanical benefits of the eshapeoko ameliorate the need for dual Makerslide X.
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roebotic
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Re: eshapeoko X and Y axes wobbling furiously!

Post by roebotic » Fri Jul 12, 2013 2:38 pm

I tried to make a video, but I can't upload it because I only have the webcam on my girlfriends mac at the minute and the forum doesn't seem to like the file type .mov. I don't speak mac so i have no way to get round this. I made two videos, one of me jogging around the X and Y axis at the same time, which it had no problem with and another of it running a very short program in which it jitters like a printer. You can't see the jittering though and the sound is distorted because the mic is picking up too much interference. I think you're right Catalin. The problem definitely isn't mechanical as it runs fine when jogging 2 axes at the same time. I guess the wobbling is from the sudden decceleration caused by the interruptions in the pulse train. I think it's either get an arduino board or source a free second hand old desktop for free. Cheers again guys.

On another note I am planning on doing my own upgrade on the X axis with some 8mm rails I pulled out of some broken old printers that I had, some Delrin acetal rail mounts (that i plan on making) and some cheap linear slide bearings, I'm hoping that will make it more rigid. What do u guys think?

I'm also looking into using the spare plastic to make new Z axis screw mounts for a trapezoidal leadscrew Z axis upgrade. As I'm in the UK everything generally costs a lot more than in the US and there aren't people making loads of shapeoko upgrades. I've found all the bits I need pretty cheap. Think I can get a 300mm length of 8 or 10mm single start trapezoidal screw for less than 5 quid and a nut for around a 10er from a company called Merchant dice. Don't know what they'd want to have the end machined to fit into a bearing though. I'm hoping to get away with spending 40 quid on both upgrades. I don't suppose anyone has a good solution for fixing a screw in a bearing without having the end machined? I was thinking of using epoxy glue, but that doesn't guarantee it'll be centered properly or accurately perpendicular.

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Re: eshapeoko X and Y axes wobbling furiously!

Post by cvoinescu » Fri Jul 12, 2013 3:39 pm

I got some screw from Marchant Dice too, to play with. I'm also trying to find a way to secure it to the bearing without machining it. I may end up making some relatively thin trapezoidal nuts for that (I'm waiting for the tap I've ordered to arrive).
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roebotic
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Re: eshapeoko X and Y axes wobbling furiously!

Post by roebotic » Fri Jul 12, 2013 4:05 pm

Out of interest, did you get 8 or 10mm screw? I was thinking of getting 10mm screw because of the slightly greater turns per mm. i think the nuts for both have the same outside diameter. If you come up with a solution for fixing the bottom end of the screw i'd be very interested.

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