Answered Troubleshooting Y axis shifting

Hello!

I got my Robo 3D R1+ this past December and have had successful prints off the bat. Recently, I've been running into issues with Y axis shifting.
I've gone thru the forums for possible solutions and have done the following:
- played and adjusted the tension of the Y belt (using the screws on the bed frame)
- cleaned and lubricated Z screws (just in case)
- verified zero switch was no obstructed and switching ok
- released the ribbon cable for the bed from the bed clip to ensure it wasn't snagging on anything
- I also ensured that nothing else was snagging underneath the bed (metal foil tape, cables, etc.)

Everything else such as X and Z and extrusion/retraction quality seem to be just fine.

Calibration cubes print out perfectly. I made some simple primitive box and cylinder shell shapes and they all print perfectly (no shifting at all). However, when I try to print more complicated shapes, like tubes that (boolean) go thru a shape along the X or Y, I noticed the shifting occurs around the bottom and a top of where the hollowed area would be. I'm wondering if the shifting is occurring due to some error in the STL files?

BTW, I am using Cura 15.04.3 because I prefer to print from an SD card and Matter Control's SD card feature doesn't seem to work properly for me.

Thanks!

 

Pictures are worth 1000 words

Did you make sure the set screw on the Y axis pulley is tight?

 

Hi Mike,

Sorry...I'm not exactly sure what the set screw is, but I think I did. I tightened the 2 allen-type screws on the Y pully (the toothed cog that drives the Y belt). I also tightened the belt enough to get rid of the 'slop' and was careful that it wasn't too tight to cause binding. The bed still moves smoothly.

I have attached some pics for reference.

One thing I noticed as I was taking the pics was in the bones_vs_clamp pic, the Y shift seems to occur near the same spot. I estimate it to be around layer 60 or so.

Also, the other thing that I find odd was that my Primitive Shell Samples all print out perfectly. Note, as a test, I printed the orange square shell AFTER the failed bones prints to see if the Y was shifted on it... but yet it printed perfectly fine.

So right now, I'm kinda stumped as to why the Y shifts on some prints, but then prints perfectly for these primitive shapes.

As I mentioned, I've been slicing with Cura. I will try printing with Matter Control and see the shifting still occurs there.

 

Ok everything there is a red flag for a loose set screw on the pulley, even though you've said you've tightened it I think we need to revisit.

The thing about pulley is a loose set screw can handle a decent amount of pull before slipping, that's why in the cases of the circles you're not seeing it as much. The transition from X to Y is where you will see the skipping, especially when it's a sharp transition like 90 degrees

Print a cal cube and see how that looks.

If you still get that slipping I want you to take the bed off, completely loosen the belt until you can remove it from the pulley. Loosen the set screws on the pulleys so you can remove the pulley completely.

In an ideal world you want to put some locktite on the set screws and reinsert them, but I never have and never had an issue.

HOWEVER, the thing i'm worried about is that the hex pattern in the set screw has started to strip out and you can't get enough tension. You really need a lot of torque because what you're trying to do is crush the two metals together to create an essentially spring force between the set screw and the motor shaft. Using loctite will help because you don't need to get quite as tight.

Give this a go and report back. If this isn't the case it might be a case of the stepper driver overheating but that's hard to say right now.

If you could watch/record it happening that would be best so we have first hand accounts of what happens when it slips

 

Ok. I will check the set screws again. It won't be able to mess with it for a couple days, but I will let you know when I do.

One thing I noticed last night when I was tinkering with the printer bed tho...
While connected to Matter Control, I was controlling the printer bed testing its travel. Every 10mm or so, I would push/pull on the bed a little bit. There were some points were it would actually slip loose and travel about 1/8 to 1/4 inch and it was usually around the middle 50 to 70mm section of the bed. I didn't get any slipping when the bed was at the further + or - extremes. Is that a sign of the set screw slipping or perhaps be an issue of the ramp motor gear?

I guess I should mention that ever since I had the printer, that when it does the auto leveling, the bed would always seem to be moved forward too far by the motor and it would jolt itself. I'm thinking this is what is contributing to the slipping and perhaps stripping gears in the motor?

 

Depends on how it's slipping. If it's the motor coil coming undone and skipping that's caused by under current on the stepper drivers. However, a faulty driver would get really hot and trip out as well, so we can't negate that possibility. Verify the fan on the bottom of your printer is running and getting sufficient airflow. Though in GENERAL a overheating stepper driver tends to stutter during long movements and is fairly obvious, but for cases of faulty it just can't really provide the correct amount of current vs temperature so you typically end up with 2 extremes, barely enough current to drive the motor when not overheating or enough current to drive the motor but overheating. This is usually resolved by a new stepper driver card.

You can test this pretty easily by engaging the motors (or do a movement, this will enable them until they time out/are disabled) then try and move the bed with a reasonable force. If it skips easily it's under current, but if it's hard to move it's fine. My misbehaving stepper driver would sort of cycle, so it would be strong for a few seconds then disable shortly, then repeat. You'd hear the buzzing sound it made as it enabled then disabled power to the motors.

Now if it's just a tiny click back and forth, then that sounds like the set screw. Why it would do it at certain location doesn't make sense though it also doesn't make sense in the case of the stepper driver either.

Mysteries!

In the event you do find it's a bad stepper driver, you can eitther A) try swapping it with a different one to see if it moves axis or B) submit a replacement part request to robo for a new one and hope it's that

Granted you should do B in either case I'd say.

 

Okay... So I finally got around to tinkering with the printer tonight and went back to revisit the set screws. Upon further inspection, I realized the set screws were not as secure and tight as I thought. I went ahead and REALLY tightened the set screws. I ran 2 prints and both turned out perfectly clean! No more Y shifting!! YAY!!

A few notes for any newbies, like me, who are just getting familiar with printer parts and with troubleshooting or repairing their ROBO 3D R1+ and are running into similar issues...

-The gear(or cog) that drives the belt for the (Y)bed sits on the Y stepper motor. I initially thought the stem(axel) from the stepper motor was a square shaped stem, but upon closer inspection, I discovered that the stem is actually mostly round with 2 flat faces in which the set screws need to tightened on to.
-When I first tried to tighten the set screws, I had removed the gear/cog to inspect it, but probably did not align the set screw properly and they did not seat properly to the flat faces, thus were not secure and still slipped.
-So when tightening, be sure the set screws align to the flat faces of the the stepper motor stem.
-Unfortunately, none of the allen wrenches that were included with the printer fit the set screws properly, so I had to use one of my own allen wrenches. Make sure that the gear/cog is inserted onto the stem down far enough so that the teeth will align with the belt properly, but also not too far that the set screws are unaccessible. I aligned mine just enough so I could get the allen wrench to the set screws.
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Anyway, I think tightening the set screws solved my Y shifting issues. Fingers crossed that it's not anything more serious.
I'm sure you will hear from me if the Y shifting persists.

Thanks for you help and guidance Mike!! I appreciate your involvement and support in these forums!

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So I am apparently a idiot how do I get the allen wrenche in thee to tight the set screw. It's recessed and my allen dose not fit do I just need a small allen wrenche?

 

You either have to take the bottom cover off and drop the motor so you can get at it.

Or I used some cheap Ball end hex wrenches like this when I tightened mine..they let you come in at an angle.

http://www.harborfreight.com/13-piece-metric-ball-end-hex-key-set-96416.html

 

Thanks I thought I might have to drop it out the bottom but I wanted to ask before I did it. I will grab some ball end wrenche those sound good.

 

So I dropped the steper and tighten the set screw. Next print was fine. Had to wait two days for new filamint to come I did the same print and had a y axis shift just one time at about 80% through the print. I added some lube and I'm trying the print again. Will update you in the morning.

 

So I forgot the Loctite and just tightened the screw I will pick some up a do that thanks all.

 

I did do Loctite worked but the issue is back I noted the quark on the bottom of the bed was sagging down. luckley my new bed had just got in but still skimping. I will cheek the steeper motor set screw might be the steeper weirs thy have come lose twice already am I missing anything i might need to cheek.