I’m having issues with my x-axis stuttering as it travels. Strangely, it is able to move from the minimum to the maximum on the x-axis with no trouble, but when it travels back, it gets to the middle and start stuttering and skipping steps. It eventually gets past whatever it’s hang up is and continues, but doesn’t make it back to the starting point due to the missed steps. If I give it a little push when this happens, it seems to be able to recover quicker, but it still doesn’t make it all the way back to the start.
From my observation, it doesn’t appear to be skipping on the belt; I can see the stepper stalling and skipping steps.
For reference, the travel in my x-axis is about 1175mm. I know that’s long, but I would think the axis should travel smoothly. L
The most likely culprit is wiring, which if it is intermittent is a bit nasty to diagnose because with a multimeter it can appear to be fine most of the time. It could be asymmetrical if there is strain (even very light strain) on a poor connection, creating a temporary open circuit. The fix is not to add strain relief but to identify the poor joint and make it robust. And then maybe strain relief in addition.
I don’t think it is wiring as it always occurs at the same spot. Interestingly, though, is that when I pulled the z-axis out of the gantry, I was able to get it to reliably run back and forth without skipping after a small adjustment to belt tension. But when I reinstalled the z-axis, it started having issues again.
If you can feel a difference when you move it by hand, even with the belts on, then you can try to narrow down why there is a physical hiccup at that location.
If it moves easily and you don’t feel anything different in the spot where it gets hung up, then it is still possible that it could be wiring and for some indirect reason (“magic”) it seems to be in the same place.
Are both sides getting hung up at the same time? This is also an indicator because it would require two independent physical events, which is possible but less likely than one electrical event.
When I push the gantry by hand, I don’t feel any hiccup as it pass through the offending portion of its range. It rolls smoothly with no apparent resistance.
I’m thinking I might need to do a slow motion video when it happens and try to figure out if both sides are stalling or only one. It’s possible that one side is stalling and causing the axis to twist stalling the other side as it binds up.
Take the belts off and check the motors individually, and check the pulleys. It is hard for use to diagnose this type of thing without touching the machine.
All right, I pulled the belts loose from the pulleys and ran the machine through it’s paces (Gcode that moves the axis back and forth through the trouble spot). With no belts, the steppers ran without issue; No skipping.
I took the center gantry off and ran the same test with just the pipes attached and it started skipping again.
I’ve tried loosening and tightening the belts, and the skipping gets worse or better, but never completely goes away.
I’ve about reached the point of just rebuilding the machine to be narrower and see if that resolves the issue. My suspicion at this point is that the belts are flexing as it moves, and when it reaches the center, the flex in both sides of the belt is causing the axis to twist and bind up.
Just because I haven’t seen in mentioned here yet – Have you set/checked the current your stepper drivers are pushing? It almost sounds to me like one of your motors is marginally underpowered…
FWIW - I know the 0.7v config value is thrown around a lot for the 8825 drivers, but I have 4988 drivers on my build and the vRef I calculated for those was 1.2v. So, if you’re not using 8825 drivers, and have them configured at 0.7v, they may be underdriving your motors?
You are already doing that basically. You took the center off and still had an issue so you are at the rollers. Either belt is too tight or the tension bolts are too tight.
I did have to tighten up the X-axis rollers because they were loose. That made things somewhat better, but didn’t eliminate the problem. The rollers now seem to roll smoothly without any binding are wiggle.
Any advise on how to know when the belts are properly tensioned? I’m mostly just going by my gut feel. I have a suspicion that I may have them too tight at the moment as the machine has now developed an issue moving away from the X-min position where it starts. And I’m running out of Zip Ties too.
Ok - yep the mini Rambo doesn’t have the little pots to adjust the current, so that shouldn’t be the problem.
Just an idea of something to try to help eliminate possible problems…
Have you tried turning the motors by hand with them powered up (but not moving) and not connected to the belts? It’s a fairly easy test to ensure that you don’t somehow have a weak motor in the mix. You might still be able to overpower them and make them turn (with the leverage of the sprockets on the shafts), but you should feel quite a bit of resistance before you get them to turn…
Again, best of luck in getting it worked out – seems like you’re quite close, but sometimes those last few steps can be quite frustrating.
Just loosen them both and see if you still have an issue.
If that is not the case your wiring must be loose or something. You have already eliminated all the issues. You aree left with belts, tension bolts being too tight and a wiring issue, there are no other issues I can think of based off what you said works and does not.
But… a picture would really help here. You have no idea how many times we spot things.
This is your most worrisome statement. The parts are an interference fit and if you had to tighten it something is wrong with your prints or rails size.
No. Not using steel belts. Bought them off Amazon using the info provided by Ryan.
I tried this when I was testing with the belts off. They were both nice and firm and took significant effort to turn.
I think this was an oversight on my part when I assembled it. I haven’t really started working on full travel until the last couple weeks. I’ll pull the calipers out and check the tube diameters to make sure they haven’t gotten dented or something.
I’ll see about getting pictures of it next time I work on it. Thanks for all the help everyone.