Only Z1 endstop works when homing

Hi all,

I am having some trouble getting dual endstops working for the z-axis on my Lowrider2. I have the endstop switches installed on both side (will attach a photo to a followup reply to this post). M119 shows that both of the Z endstops are working as expected, so they both indicated TRIGGERED when they are supposed to and open otherwise. Also, moving Z in the positive direction moves both sides up.

However, when I try homing using Auto Home Z (both from the LCD display and Repetier Host), the firmware does something unexpected: it only seems to stop moving Z if the Z1 endstop is triggered, and ignores Z2. Also, it does not back off and retry after hitting the limit on Z1, it just kind of hangs and stops accepting commands. Once movement stops, Z2 remains frozen wherever it was. If Z2 hits the end first, it keeps going and I have to pull the plug to prevent damage.

I am using this firmware with no modifications to any of the files: V1CNC_Rambo_DualLR / 510

Any idea what I might be doing wrong?


I am using a Rambo v1.4 board. Here is a photo of one of the Z endstops.

My guess is that they are swapped, so the Z2 endstop is triggered, stopping the Z1 motor.

Hmm, I double checked and when I trigger the Z1 endstop manually M119 reports:

21:20:52.751 : Reporting endstop status
21:20:52.751 : x_min: open
21:20:52.751 : y_min: open
21:20:52.751 : y2_min: open
21:20:52.751 : z_max: TRIGGERED
21:20:52.751 : z2_max: open
21:20:52.751 : z_probe: open

And manually triggering the Z2 endstop gives:

21:33:06.938 : Reporting endstop status
21:33:06.938 : x_min: open
21:33:06.942 : y_min: open
21:33:06.942 : y2_min: open
21:33:06.942 : z_max: open
21:33:06.942 : z2_max: TRIGGERED
21:33:06.942 : z_probe: open

So I think this is correct, right?

That looks right. Are you sure you have Z1 and Z2 motors where you think they are?

Yep double checked that too. I did get it to work once, when they were both close to being aligned already. The auto home Z did what it was supposed to do. I am wondering if I need to up the voltage on my drivers a bit. I noticed the Z1 was having trouble lifting when the router was on that side. Maybe they are a bit underpowered currently?

If they can’t reach the steppers that would do it. Or if they were binding when they got higher or out of square.

Can you just tap both of them instead of letting the motors get there?

OK. I gave that a try. If Z1 triggers first I can only get the home Z to complete if I manually trigger Z2. Here’s the video:

Any ideas?

Could this be a problem with the dual trigger offset, or whatever it’s called. I remember reading something about when you have dual end-stops that if one triggers, and the other doesn’t trigger within n distance, then it aborts the homing cycle.

Boy. That is super weird. I am not sure about that. It doesn’t look like it is struggling at all to raise the gantry.

Seems like it might be a firmware issue to me. Any chance that someone can confirm that / 510 works correctly for them with Z-axis home with dual endstops?

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In the meantime, I’ll try some older versions to see what happens.

Figured it out… I did not replicate the connections in this table correctly:

Motor Driver Endstop
X X Xmin
Y1 Y Ymin
Y2 E0 Ymax
Z1 Z Zmax
Z2 E1 Xmax

I had my Z2 motor connected to the Z port beside Z1… I guess that makes sense that it was doing whatever Z1 was doing.

When I corrected that, everything started working flawlessly!!!

Thanks for the help to debug this.


Oh, of course. Sorry, I could have guessed that. I should have asked for a photo of the board.

And bonus, we have another person who has tested the DualLR version on v510. Thank you.

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It’s part of why I like the MPCNC projects so much. Building my own CNC from basic components really makes me understand how everything works, and how to fix things when they go wrong!

Next issue I have is that I messed up something mechanical and the x axis rails aren’t equidistant from the table surface. Maybe my yz assemblies aren’t square? Not sure… when I rest the x rails on some blocks of wood, they sit nice and flat as long as the wheels aren’t touching down. But if I lower the wheels to the table, it is apparent that one wheel is higher than the other.The wheels lower more on one side than the other. This happens the same on both sides…

Is there twist in the gantry pipes? Maybe loosen them a little and see if it settles down.

I think I figured it out. The z-axis pipes weren’t properly perpendicular to the x rails. I played around with the four screws on each side to square them up and it seems to have done the trick.

Now the x rails are pretty close to the same distance from the tabletop all the way along. There does seem to be some deviation or flex in my pipe (maybe up to 1/16”) but I assume that that is to be expected. Can you confirm?

Here’s a short video showing what I mean:


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