LR2 dual end stop - miniRambo - necessary?

Good morning, me again !

So, reading some documentation on end stop, I do have a question as I admit I’m slightly confused…

We will need to cut material on both sides, so we need a precise homing mechanism. Our current LR2 setup is not using endstop.

So questions are:

  • Are “hardstop” accurate enough for sub mm accuracy when homing
  • if replacing with endstop, why wouldn’t this work with a miniRambo (as I’ve read you need a 5 channel control board, but I must admit I’m not quite sure of the why)
  • This link here is dead (I found a reference to it in older threads): as all dual endstop documentation is referring to LR3 now. Any link to the LR2 dual end stop documentation ?

Thanks !

Hello Vincent,

the hardstops on my Primo were pretty spot on, maybe 0.2mm off, but it took a while to configure them. There are a lot of ideas floating around this forum on how to achieve it with a LR2.

You need 5 channels, because otherwise the software stops the whole axis when the endstop triggers (if you have two drivers connected to one channel, it does not matter whether you connected two endstops, it will trigger as soon as one gets triggered and the whole axis stops), so it does not help you to achieve squareness at all.

The LR3 was the first version to have dual endstop firmware available when it came out. But the documentation is essentially the same.

After you engage the motors, they move in lock step. The two Y and two Z will stay at whatever squareness you started with. If you use some kind of hard stop to align them before you engage the motors, then they will stay that way unless they skip steps or are disengaged.

If you had 5 drivers you could auto square. Each of the Z motors would turn independently until they each touched their own endstop. Same with the dual Y. This would make the position and the angle of the gantry repeatable between jobs and sides.

If you only have 4 drivers, you can’t drive the extra motors independently. So you don’t get autosquare with the mini rambo.

I think starting the motors against hard stops is reliable enough for repeat jobs in wood. But you would have to measure the tolerances and decide for yourself.

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Ah so dual endstop is not about homing accuracy, it’s about squareness. Got it, and it makes sense indeed.

But for Z, that implies homing up, instead of homing down, right ?

if my need is only homing, then I should be able to get away with regular endstop (one per axis), right ?

I don’t know exactly how the LR2 works, but the LR3 homes up, correct. :slight_smile:

If you really only want to home, you can get away with one but then you could just push it against hardstops, that’s faster. :smiley:

If you aren’t reliably square, then you aren’t going to get reliable homing. You can use single endstops (the firmware already supports them NC on XY, touch plate on Z). But if your other motor is not square, the position will be wrong.

Put another way, you can’t get positional accuracy until you have squareness accuracy. You can have square accuracy without positional accuracy.

Well conceptually, I could just use four endstops (two for X, one for Y, one for Z), provided I can configure Marlin for that purpose, and hope that my Z gantry alignment is mechanically correct, but that’s probably easier just to go out an buy a full sized Rambo and put the mini aside (I have a need for it anyway for a Zen table, so it won’t go to waste).

I’m just trying however to find assembly pictures on the best location for end stop for LR2, any pointer / picture ?


That is one reason we didn’t document endstops for LR2. It didn’t have their placement designed in. You’ll have to scrape the forums.

It is possible. I don’t have preconfigured versions for this.

You can configure Marlin for this, and it could work. It’s a matter of how much work is it worth?

For me, editing firmware isn’t a big deal, but it’s still work to do, and I’d usually rather do other stuff. (I code for a living, so it’s not difficult, but it’s hard to ignore work time compared to my wages.) For an hour’s wages, I can buy a nice board that I can drop in and go. (Though saying that, I use Duet boards with different firmware that needs configuration editing… In my defense though it takes me less time to reconfigure for a V1 machine than it would to recompile and install a new Marlin firmware.)

I will admit to often going a “cheap” way that is only inexpensive if I value my own time at $0/hour, particularly for hobbies, but this only works for me if I’m solving new problems. Once I have the solution worked out, it’s just work. This is why so many of my projects get done as far as “proof of concept” builds and never get a nice finished build. Example: I have a DIY video projector still in the “good enough for now” box I built for it in 2007.

Anyway, my point is that it may be worth evaluating the cost of a 5 driver control board that has “just works” firmware. The SKR 1.4 board for example…

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Well that’s exactly why I just ordered a SKR Pro 1.2. As you state, spending time configuring the firmware is not something I want to do (although I do know how to do it, VSCode and PlatformIO are installed on my system).

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