Mini Rambo vs MKS board?

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JonJahaerysSnow
Posts: 5
Joined: Wed Aug 16, 2017 6:46 am

Mini Rambo vs MKS board?

Post by JonJahaerysSnow » Sun Jan 28, 2018 2:09 am

So I caved in and got a cheap mk42 clone from ebay and planning to get an el cheapo pinda clone. Now I'm wondering if I should use a Rambo board or if I should stick with a regular MKS board with a modded firmware. My reasoning is that with the Rambo board I'll be able to use the original prusa firmware with its bed leveling functions, but I'd also like to use a 12864 screen fo which an MKS board would be perfect, but then I'd lose Prusa's autolevel and would have to use a modded Marlin and risk not being able to update as quickly as if I was using a vanilla version of Marlin. I'm totally at odds and absolutely indecisive about what to do. Any advice?

slippyr4
Posts: 224
Joined: Thu Jun 15, 2017 10:24 am

Re: Mini Rambo vs MKS board?

Post by slippyr4 » Sun Jan 28, 2018 9:02 am

Disclosure: the modded firmware is mine.

I don’t think it really matters what you choose, they are similar boards.

You won’t get the 128x64 working on prusa firmware with either board; there’s not enough code space left over and the support for it has long been stripped out of prusa fw.

If you really want that lcd then you will end up running marlin. It’s easy to configure marlin for either board, they are both well supported.

However, I don’t think there is much point in the LCD. It doesn’t actually do anything that the character lcd doesn’t, apart from the little pictorials of hotends.

Probably the most important thing that running prusa fw will get you is the live Z adjust. If your mk42 is a proper FR4 one (and not one of the aluminium ones that are now appearing on AliExpress) then you will find it much easier to get bed levelling working on prusa fw; on marlin it’s harder to get it to probe the correct locations on the bed.

My choice is always the MKS GEN because it’s a lot cheaper for a product that is only marginally inferior quality. But each to their own.
Self-built Prusa i3 MK2 clone
My things: https://www.thingiverse.com/slippyr4/designs
My Prusa firmware port for ramps & MKS : https://github.com/slippyr4/Prusa-Firmware

JonJahaerysSnow
Posts: 5
Joined: Wed Aug 16, 2017 6:46 am

Re: Mini Rambo vs MKS board?

Post by JonJahaerysSnow » Mon Jan 29, 2018 12:13 am

Thanks a lot Slippy.

The 12864 would be nice to have, but I can live without it; the main priority is the bed leveling feature because I just spent a niche chunk of change on this clone.

Is a Prusa style bed leveling procedure achievable on an MKS board running Marlin and a cheap pinda clone or should I go with your modded firmware?

slippyr4
Posts: 224
Joined: Thu Jun 15, 2017 10:24 am

Re: Mini Rambo vs MKS board?

Post by slippyr4 » Mon Jan 29, 2018 9:40 am

The issue, if you want to call it that, with the MK42 is that the bed levelling with the induction probe relies on the 9 calibration points on the bed. All these are is round copper pads, but they are surrounded by copper heater traces.

The sensitivity of an inductive probe varies with the type of, and amount of, metal it's exposed to. So, in the case of the MK42, it will trigger higher above the calibration points than other parts of the bed.

This means that whatever firmware you use, you need to be sure that it probes these 9 points, and not other locations on the bed. Prusa firmware is designed to probe these exact points, yet marlin is not.

However, marlin's bed levelling (which i've not used since before the UBL update) allows you to specify the grid size (3x3) and offsets, so it's feasible (but i've not tried) that you'd be able to get it to probe the right points.

Also since there's no mechanical endstop you need to use Z safe homing and ensure that the X,Y coordinate it positions itself at for homing Z is one of the points.

All that, for the ability to use the 128x64 lcd. The downside you have with marlin is that there isn't an easy menu option for tuning your Z height. Prusa FW has "live adjust Z" which really is an easy access to editing the value for M851. You can do M851 manually on marlin but it'll be a bit tedious and iterative to get the right Z tramming - remember, a MK2 has no bed adjustment screws so it's all done electronically.

I personally don't think there's anything useful in marlin that isn't is prusa FW. However, since each lcd is available for less than $/£/€ 10, it's not that much of a risk to try whichever one you prefer over the other!
Self-built Prusa i3 MK2 clone
My things: https://www.thingiverse.com/slippyr4/designs
My Prusa firmware port for ramps & MKS : https://github.com/slippyr4/Prusa-Firmware

oakdesign
Posts: 109
Joined: Thu Jun 15, 2017 10:21 am

Re: Mini Rambo vs MKS board?

Post by oakdesign » Mon Jan 29, 2018 4:34 pm

All that, for the ability to use the 128x64 lcd. The downside you have with marlin is that there isn't an easy menu option for tuning your Z height. Prusa FW has "live adjust Z" which really is an easy access to editing the value for M851. You can do M851 manually on marlin but it'll be a bit tedious and iterative to get the right Z tramming - remember, a MK2 has no bed adjustment screws so it's all done electronically.
I have to contradict that statement.
You can set the Z Offset through Marlin Menu and with BABYSTEP_ZPROBE_OFFSET enabled not even set but also live adjust the probe offset

Code: Select all

#if ENABLED(BABYSTEP_ZPROBE_OFFSET)

      void lcd_babystep_zoffset() {
        if (lcd_clicked) { return lcd_goto_previous_menu_no_defer(); }
        defer_return_to_status = true;
        ENCODER_DIRECTION_NORMAL();
        if (encoderPosition) {
          const int16_t babystep_increment = (int32_t)encoderPosition * (BABYSTEP_MULTIPLICATOR);
          encoderPosition = 0;

          const float new_zoffset = zprobe_zoffset + planner.steps_to_mm[Z_AXIS] * babystep_increment;
          if (WITHIN(new_zoffset, Z_PROBE_OFFSET_RANGE_MIN, Z_PROBE_OFFSET_RANGE_MAX)) {

            if (planner.leveling_active)
              thermalManager.babystep_axis(Z_AXIS, babystep_increment);

            zprobe_zoffset = new_zoffset;
            lcdDrawUpdate = LCDVIEW_CALL_REDRAW_NEXT;
          }
        }
        if (lcdDrawUpdate) {
          lcd_implementation_drawedit(PSTR(MSG_ZPROBE_ZOFFSET), ftostr43sign(zprobe_zoffset));
          #if ENABLED(BABYSTEP_ZPROBE_GFX_OVERLAY)
            _lcd_zoffset_overlay_gfx(zprobe_zoffset);
          #endif
        }
      }

    #else // !BABYSTEP_ZPROBE_OFFSET

      void _lcd_babystep_z() { _lcd_babystep(Z_AXIS, PSTR(MSG_BABYSTEP_Z)); }
      void lcd_babystep_z() { lcd_goto_screen(_lcd_babystep_z); babysteps_done = 0; defer_return_to_status = true; }

    #endif // !BABYSTEP_ZPROBE_OFFSET
Opa's bester Rat: Probieren geht über Studieren, Grandpas best advice: the proof of the pudding is in the eating

JonJahaerysSnow
Posts: 5
Joined: Wed Aug 16, 2017 6:46 am

Re: Mini Rambo vs MKS board?

Post by JonJahaerysSnow » Mon Jan 29, 2018 8:01 pm

All right, then Mini Rambo + Prusa firmware it is! Thank you so much!

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