Question about endstops on a CoreXY machine



  • Hi,

    I'm working on a CoreXY machine that started life as kit of parts from China with the printed parts done by Shapeways.

    The X gantry has a endstop switch for homing. Naturally this allows homing X at any position of the Y gantry. Of course this means there are a set of wires for the X endstop switch running to the gantry and the associated need to handle the movement of the wires as the X and Y gantries move.

    But I got to thinking - is it really necessary to provide for homing X at any Y position?

    If Y is always homed before X, then the Y gantry would be in a fixed position when X was homed and the endstop switch for the X axis could be installed at a fixed position on the frame rather than on the X gantry.

    Is there any reason, in the real world, that this would not work?

    Thanks much.

    Frederick



  • You're in control of the homing process, so if you can ensure that the Y gantry can place the carriage in the right position to hit the X endstop then sure, go for it.

    The default position of the DBot Y endstop is at the back right and the X endstop moves to the left, so if you homed Y first to get the gantry to the back and then had the carriage move to the left the endstop could be tucked at the back left.

    You'd lose the ability to home X and Y at the same time in homeall to save some time, but that's not a big deal.

    And your homex.g would have to home Y first.



  • @phaedrux

    Thanks for the feedback.

    There is not too much left of the original DBot design. I'm still using the four top corner printed parts. And the X and Y gantry are still the original "wheel-on-extrusion" design but that may soon change.

    I've finished up the new Z axis setup (using MGN12 linear rails, 8mm lead screws and one big stepper). I much prefer it to the two motor, cantilevered, "wheels-on-extrusion" design of the DBot. I did set it up that way to start - I just didn't like it.

    My first cut at installing the bed wasn't to my liking but the current approach is going to be fine. Just need to print some parts to verify the fit before I machine them in aluminum.

    I've gained a bit of build space. The original 300x200x300 could be expanded to 300x250x330 but I already have the parts for a 300x200 bed so I'm going to use them. I still get the additional 30mm on the Z axis.

    I've retired all my deltas so I need this printer up and running to backup my FT-5.

    Thanks again.

    Frederick



  • That's a good observation. The Hypercube Evolution for example has the X endstops (two of them) on the gantry.

    With the Duet you can also dropt the X,Y endstops and just used motor stall detection. I went this route and am happy with the results and the simplicity. For Z you can just use a level sensor such as BLTouch.

    Another interesting CoreXY homing goes like this (try manually), rotate one motor while the other is free, you will see that the gantry will move diagonally and then along the edge until it reach a corner and then stop.



  • @fcwilt It would work but you still need to run wires to the hot end heater, thermistor, fans etc. So it's only 2 wires out of many. In fact, it could be only one wire by using a common+. The downside is that you won't be able to coarse home X and Y together and neither will you be able to just home X on its own. Whether that loss of functionality is worth the gain of running one or two less conductors to the carriage is a choice that only you can make.



  • I used to have the X endstop on the extruder carriage, but I am always looking for ways to reduce the number of wires going to the carriage to maximize reliability (and ease connector selection) and moving the X endstop was a no-brainer. I mounted it on the printer's frame and then set the config file to always home Y before it homes X (in the homex file). It has never failed to operate correctly.

    What I'd like to be able to do is run only power and a serial data line to the extruder carriage. That would minimize the wiring and connector issues but require some electronics on the carriage.


  • administrators

    @mrehorstdmd said in Question about endstops on a CoreXY machine:

    What I'd like to be able to do is run only power and a serial data line to the extruder carriage. That would minimize the wiring and connector issues but require some electronics on the carriage.

    This will be coming, in the form of the Duet 3 Smart Tool board. Essentially it will be a cut down version of the Duet 3 expansion board with support for (provisionally) one stepper motor, one heater, two fans, one thermistor or PT1000, a Z probe, and some sort of LED lighting. It will talk to the Duet 3 main board over CAN bus.



  • @dc42 Ohh! Count me in to be a beta tester when it's ready!



  • @dc42 said in Question about endstops on a CoreXY machine:

    This will be coming, in the form of the Duet 3 Smart Tool board.

    This is going to be a very popular add-on!

    What will be the total wire count including the power?

    Next thing we will need is a bowden tube with integrated conductors 😉


  • administrators

    @zapta said in Question about endstops on a CoreXY machine:

    What will be the total wire count including the power?

    Four: two power wires (with enough rated current to power everything) and one twisted pair for the CAN bus. We are using RJ11 connectors for the CAN bus, because RJ11 cables are easy to source.



  • @mrehorstdmd said in Question about endstops on a CoreXY machine:

    I used to have the X endstop on the extruder carriage, but I am always looking for ways to reduce the number of wires going to the carriage to maximize reliability (and ease connector selection) and moving the X endstop was a no-brainer. I mounted it on the printer's frame and then set the config file to always home Y before it homes X (in the homex file). It has never failed to operate correctly.

    What I'd like to be able to do is run only power and a serial data line to the extruder carriage. That would minimize the wiring and connector issues but require some electronics on the carriage.

    Thanks for the info. Good to know it works in the real world.

    I like the idea of reducing the wiring to a minimum. The upcoming Duet 3 line seems to have a solution in the works.

    Frederick



  • @dc42 said in Question about endstops on a CoreXY machine:

    This will be coming, in the form of the Duet 3 Smart Tool board.

    Brilliant! Sign me up! Put me in the queue or whatever!

    In the meantime I will work on the explanation for the wife as to why I need to replace all my Duet 2s!

    Frederick



  • We are using RJ11 connectors for the CAN bus, because RJ11 cables are easy to source.

    They may be on the large size for a two data wires connector but I don't know what the board size.

    Since you have local sensing and control, you can also implement local safety, independent of the main board. E.g. shutting down the heater in case of over temperature, bad sensor, unreasonable commands from main board, or communication loss, but I am sure you already thought about it. ;-).

    I love this idea. Moving the complexity from copper to silicon.


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