Y-Axis Has a Flat Tire - Maybe

Hey folks, I’ve got an odd problem. I’ve read lots of entries here and on the web about folks having issues with bad steppers or mis-wired steppers, or eccentric nuts too tight, etc.

My issues seems to be a little different. Even before I put the belts on the Y-Axis, like any kid with a new toy, I pushed the gantry around to just see it move. I was able to keep myself from making Vroom Vroom noises, but only barely. As I pushed it back and forth, it would “thump.” Just like a car with a flat. It’s repeatable and rhythmic. Actually, it is more like when you are driving at speed and hit those breaks between concrete sections. You can actually feel it in the gantry.

As I sit here and type, I realize I should have marked the V-Wheels with white paint to confirm if the “thump” always happens at the same point when the wheel turns. Will do that tomorrow.

But this phenomena makes me think that one of my V-Wheels as a flat spot on it. But I’ve felt around the grooves of all 8 wheels and I can’t feel any flatness.

I put the belts on, finished up the assembly. And my X and Z axis move super smooth. But these bumps really make a big impact. I think I probably need to increase the POT for the Y. But if there is some physical issue with the gantry, I don’t want to try to “power” through it by jacking up the power on the Y.

Any ideas on what I should check next? I do have a whole set of V-wheels I could swap out, but really want to check all other options before I do that. Is it possible one of the ball-bearings might be buggered?

Sorry, I’ll stop throwing ideas and ask again, any ideas on what I should check next?

Thanks

Rob

I’ve found that they are all pretty soft and go flat from just sitting.

One of these days, I’ll write some code to move everything around for a while to let them get back to round and then check for the bumps.

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Hey @TonyNo, thanks for the reply. I appreciate it. It would never have dawned on me to move it around to get them “back to round.” Great idea!

I wanted to clarify that I observed this immediately after installation of the Y-Axis, within seconds of putting on the rail end-plates. I have also observed that even after sitting a few weeks without moving, the X-Axis - which presumably is carrying twice as much weight as each of the two Y-Axis plates - is still super smooth in movement.

I think I’m going to go ahead and change out the V-Wheels. A friend pointed out that it’s not possible for me to get my fingers deep enough into the groove to detect a flat spot. And in hind-sight, he is right. I’ll do that and update this thread.

Maybe a dumb question…

Does it only occur when you push it quickly? Mine “bumps” or vibrates when I manually push it quickly. If I move it slowly, it’s smooth as silk.

Suspect (on mine anyway) that this is something to do with the current produced by the motors when you push them around - you’ll see the lights come on, on the card when you push the gantry around.

Is this what you’re seeing?

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Yep, it is becase they are wired together, opposite of eachother each acting as a generator to drive the other motor the other way.

More info here:

Yes, I’ve always loved this, but have yet to find a practical use for it. Apart from potentially damaging the card, I wondered if this was what the “bumps” we’re he was feeling.

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Hey folks, thanks for the replies.

@RobertCanning - thanks for the cross-post. But the bump was first observed when no belts were present. Still present with belts. And yet still present when I removed the belts in testing.

@DavidWestley - fast or slow. With belts or without. Sigh.

All of that to say, without the belts attached, the steppers don’t even come into play. Very frustrating.

Thanks guys. Really appreciate the thoughts. Wheel replacements this weekend I guess.

As you push the gantry along, hold your fingers against the wheels and tracks each end, feeling the movement along the rails. When it “bumps” are both ends bumping together (at the same time) and by the same amount? If things are out of square, this bump could be one end ‘catching-up’ or realigning itself with the other.

Are all the gantries straight and parallel? Is the bump, one of the gantries being pushed or pulled out of line (or back into line). Are the V Wheels ‘riding-up’ the makerslide and the bump is when they re-align themselves or fall back into alignment?

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Hey folks! Success - kinda.

A while back I built a camera slider. So had a “known” good piece of makerslide. I didn’t see @PhilJohnson’s comment until it was too late to try his idea. But I did take the left gantry plate off and tried it on the “good” makerslide. Yep. Thump thump thump. Since it was just the gantry plate on a spare slide, squareness, belts, and steppers didn’t come into play.

I chucked the four v-wheels, put on new ones, put the plate back on, squared it up again. And boom. No thump.

Guess I’m just lucky. Actually, I really am since I picked the right plate to start with.

Anyway, thanks for all the support!

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I replaced the wheel and the bearings - The whole wheel. I didn’t know if it was a problem in the v-wheel or the bearings or what. And to be honest I was so frustrated by that point I didn’t care. Lol. Sorry I couldn’t provide more info.

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@PhilJohnson

Totally good. And I don’t feel too bad about the experience. I was totally convinced at first that it was a square issue. So I must have re-squared the machine half a dozen times. So I’m pretty good at it now. Probably should write a blog post on my technique.

Only deal now is that I’m regretting throwing away all four wheels. I should have taken the time to figure out which one was the offending party, and written up some observations in case that might help someone else at some point. But I was just so frustrated, and happy to have made some progress, and to get carving. Hopefully, this was just a freaky fluke. I tend to attract them like lightening strikes.

Carved for several hours now. Only issue I’ve had since is I screwed up and didn’t have one of the work pieces screwed down tight enough. Live and learn right? But aside from that, I’m a really happy camper right now!

Thanks for the follow up! I appreciate it!

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I have had two wheels on my x axis actually split into two pieces. I can see where the delrin could be damaged and have a bad spot in it. Glad you got it figured out.