Problems with Z Axis Skipping Steps

LowRider CNC Troubleshooting
1

Hey all!

I finally got to put together my Lowrider! I’ve been having problems with the Z height though. My X and Y axis are working as expected, but when I try to raise my Z the motors skip like crazy. I’m running grbl on a rambo1.4 with the kit that is offered in the store with things wired for dual endstops (I haven’t plugged the endstops in yet, but I have individual wires for each motor). If I apply upward pressure to the gantry then it will raise. I have a 2.2kW spindle in the gantry, so afaik it shouldn’t be too heavy.

Am I missing something here? Are there settings in USG that I need to modify (I’ve been running it out of the box)? Is there something wrong with my motors and I need to get stronger ones? Am I just moving them too fast?

2

It’s either not enough Z motor current, or your steps are wrong. Post up your config part for the steppers. Also, how much does that spindle weigh?

3

I second Barry’s opinion regarding stepper motor current being the first thing to check.

4

Does the gantry move freely up and down?

5

Where would I find that? I haven’t configured anything in UGS and I’m using the grbl firmware what was posted on this site. I don’t have a scale nearby, but the spindle doesn’t feel like it weighs any more than a hand-held Milwaukee router with battery.

6

The gantry does not move freely up and down when the board is on. If I cut power to the board then it will fall down, but I think that’s to be expected. I can turn the motors by hand when the motors are on or off, but when the motors are off I can’t just raise the gantry, it picks up the y-plates.

7

Right. With the steppers off, you should be able to spin the lead screws by hand, might need to help by lifting the gantry with your other hand. Check for any binding. As for the firmware, no idea, I’ve not touched grbl yet.

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8

Ok, I’ll look into it. Would that setting be in the gcode sender, or in the firmware for the board?

9

It might be a $ setting, but my guess is it is in the firmware config.h file.

10

Hey Jeff!
I’ll check the $ settings on Monday as I know how to mess with those, but I’m not sure at all how to mess with firmware config files. Do you know of any resources that can get me started with firmware editing? Cheers!

11

That I know of its is in firmware no $ setting I’m aware of. I don’t know the settings as I set mine manually on a ramps board

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12

Tim, do you know what the setting is called or what line it is on?

Lou, you would change the file and then recompile and flash the firmware again.

13

No I have not looked into it yet not having a rambo sorry

14

I think this is the post

15

It looks like they are in the config.h, at least in this version:

16

Ok! Any idea what the value means? Is it 1.35A or something else? I’m having some trouble finding documentation for this stuff. Should I just increase the value slowly (like +5) until it starts working?
Thanks for all the help you guys, I’m completely new at this and probably asking questions that I should know how to answer.

17

135 is very close to right. They have a funky translation. I think the marlin firmware is set to 138 or 135.

18

I’ll try 138 on them tomorrow and see what happens.

19

I tried bumping the current value up to 138, but nothing seemed to change. I was looking at my board and it looks like there’s only 5 controllers for the 6 pinouts with the z axis sharing a controller. Is there a way to shuffle down one of the z pinouts so that every motor has a single controller? I’m hoping that would fix the issue, but I don’t know how to do that.

20

Interestingly, all my motors are warm except my Z axis.