Delta 4th axis length and limits?



  • Intro

    I working on a 'flying' extruder based on the newish addition of extra axis on delta's. I am wondering what happens if the usable travel length of the 4th axis is shorter or longer than what would be required?

    Setup

    For example, my delta has a homed height of 634mm with a 4th axis located at (0, 0). My extruder should be a be able to swivel in a directions for a maximum of 55° from the bed normal. Combined with a 446mm diameter bed, the virtual diagonal rod would have to be ~272mm.
    If we make the assumption the print head only moves up and down at (0, 0) you would need a usable travel length of 634mm , located from Z=272 to Z=906. Adding X/Y moment in the mix, you would need to lower the Z=272 to Z=156 for the hotend to be able to reach the bed edges. If my old cos and tan's are correct, a 4th axis travel of 790mm is required (from Z=156 to Z=906).

    Question

    How does the firmware deal with shorter or longer upper limits? What happens if the 4th axis endstop is located higher than the what the machine can reach based on all the rod legths etc. Same question for when the endstop if located lower, so the 3 main tower endstops cannot be reached. Bonus question, do you need a endstop at the bottom of the 4th axis as well?


  • administrators

    RepRapFirmware won't handle that configuration properly. However, you should find that the travel needed for the 4th axis is less than the travel needed for the main towers. I expect your main rods are about 540mm long and the carriages go up to about 1080mm. So between the extruder outlet at the top of its traveland the top of the machine, you should have around 170mm, in which to fit the extruder and the 4th axis mechanism. If you need more space, then the 4th axis mechanism will need to protrude from the top of the machine.

    You don't need an endstop at the bottom of the 4th axis.



  • @dc42 My diagonal rods are 500mm long with carriages mounted on 1000mm mgn12 rails, so you were fairly close 🙂 . Can you elaborate on what won't work in that setup (and do you mean my IP setup, or a setup with sorter limits?)


  • administrators

    What I mean is that you need to set the homing switch height for the 4th axis such that when all 4 switches are triggered, the extruder is at the correct distance from the effector, or at least close enough not to be a problem (you can fine-tune the 4th homing switch offset in the M666 command).



  • @dc42 said in Delta 4th axis length and limits?:

    What I mean is that you need to set the homing switch height for the 4th axis such that when all 4 switches are triggered, the extruder is at the correct distance from the effector, or at least close enough not to be a problem (you can fine-tune the 4th homing switch offset in the M666 command).

    I see, that is an important piece of info. Does RRF assume the homed height is the same for all axis, ie. once the machine is homed it is assumed the 4th axis can move 634mm down in my machine, or how does that work?


  • administrators

    Once the axes have been homed, RRF assumes that all axes can be moved by the amounts needed to reach the defined build area.



  • Thanks for the info @dc42, I think I can continue the design process. I see what I come up with in a few weeks/months and post here.



  • Some minor tweaking here and there is expected but normally the design for my 4th axis extruder should be completed. All the parts are printed and will probably installed tomorrow 🙂
    On the arm a Pi with a camera is mounted near the carriage. The extruder (Bontech BMG) will be installed in a gimbal style mount so it can swivel in all axis, to minimize the required bowden length.

    0_1564007053258_2019-07-25 00.11.13.jpg



  • Following with great interest.



  • @danal said in Delta 4th axis length and limits?:

    Following with great interest.

    I can already tell you that the first version I designed of the 4th axis worked quite well. The arm was printed to heavy and the carriage I used wasn't ideal but it did it's job.



  • @Nxt-1 said in Delta 4th axis length and limits?:

    @danal said in Delta 4th axis length and limits?:

    Following with great interest.

    I can already tell you that the first version I designed of the 4th axis worked quite well. The arm was printed to heavy and the carriage I used wasn't ideal but it did it's job.

    Thanks to this thread i'm very keen on having this on my heavily modified Anycubic Predator.

    You mentioned that the first version worked quite well. Have you had any other revisions since?

    What challenges did you encounter when designing and implementing the fourth tower?

    Got a video of it in action?

    In my case, I'm running a zesty nimble remote drive extruder. I'm planning on using a shorter drive cable and have the extruder motor, some-what in the middle, with a gimbal to minimise forces that the cable would exert on the effector. Also, I'll add the berd-air pump to the forth tower to reduce the length of the air tube and reduce the pressure drop that a longer air tube would induce. Perhaps also add the filament spool to the other side to reduce the length of filament to the hot-end. All just ideas at the moment. Will be interesting to see how it turns out in practice.

    Anyway, I'm interested in hearing your thoughts.

    Thanks,



  • @Munce31 I have not got any recent pictures and I am not near my machine for the week. I will take some if I remember next weekend. I can tell you that I still use something very similar to the picture I posted above.

    The arm has gotten way more complicated (and heavier) since I added a full blown water cooling setup on there. At the moment I a working on a simple counterweight systems to offset the ~2.2kg of mass that the moving arm carries.

    If you are interested in the water cooling part you can check out the ongoing project in this thread.



  • Here is what the latest iteration looks like in CAD.
    Clipboard01.jpg



  • @Nxt-1

    Wow that looks like a fantastic piece of engineering. I guess you're printing in a heated chamber environment.

    I see that your tower is driven by belt, so how do you prevent it from falling down with all of that weight on it?

    Also, am I right in saying that you can have the 4th tower's end stop lower than the end stops of the delta towers?



  • Also, I'm wondering if there is a way to make the 4th tower move simply as an offset of the Z height?

    My understanding is that the current coding in RRF is for flying extruders, so it tries to maintain 'X' amount of distance between the extruder output and the hot end's entry point, effectively the length of the bowden tube.

    The scenario I'm thinking of is for cameras, where you want the field fo view to remain at the same level or offset of where the print head currently is in the Z orientation.


  • administrators

    @Munce31 said in Delta 4th axis length and limits?:

    Also, I'm wondering if there is a way to make the 4th tower move simply as an offset of the Z height?

    My understanding is that the current coding in RRF is for flying extruders, so it tries to maintain 'X' amount of distance between the extruder output and the hot end's entry point, effectively the length of the bowden tube.

    The scenario I'm thinking of is for cameras, where you want the field fo view to remain at the same level or offset of where the print head currently is in the Z orientation.

    As I said in another thread, you can achieve this by pretending that the 4th tower has a very long rod length.



  • @Munce31 said in Delta 4th axis length and limits?:

    @Nxt-1

    Wow that looks like a fantastic piece of engineering. I guess you're printing in a heated chamber environment.

    I see that your tower is driven by belt, so how do you prevent it from falling down with all of that weight on it?

    Also, am I right in saying that you can have the 4th tower's end stop lower than the end stops of the delta towers?

    Actually I do not have a heated chamber. I incorporated water cooling, because I could 🙂 and to avoid 'tiny fan noise' where possible.

    The whole system is indeed belt driven. During operation the power of the motor is enough the overcome the weight, albeit just. The stepper I had laying around when I started working on this is not terribly powerful, I might swap it later but it is fine for the time being.

    In its current form the issue arises when the power is switched off. For now I have written a shutoff script that moves the head to the edge of the bed at Z=0, so the 4th axis is as low as I can be. Only then is the power actually turned off. This minimizes the distance the carriage will drop. To resolve this, I have started working on a simple counterweight system. On the cad picture I posted you can spot the wheels where the cable will run over at the top (in a upside down 'U' shape). I have not completed everything I need for this to work, so no pictures yet.

    With regards to the 4th axis endstops. Unless I am mistaking, you can place them at any height you want. The only thing RRF requires/assumes is that when the machine is homed on all axis, the (vertical) distance between the 4th axis endstop and the attachement point at the other end is the correct distance you specified in the config.g file. It as to assume this as there is no way to probe this similar to the actual printhead.


  • administrators

    @Nxt-1 said in Delta 4th axis length and limits?:

    With regards to the 4th axis endstops. Unless I am mistaking, you can place them at any height you want. The only thing RRF requires/assumes is that when the machine is homed on all axis, the (vertical) distance between the 4th axis endstop and the attachement point at the other end is the correct distance you specified in the config.g file.

    That's correct.



  • @Munce31Here are some crude pictures I took yesterday. Sadly no video yet, I hope to get some things completed in the coming month or so before I make a clip.

    2019-11-17 10.40.09.jpg 2019-11-17 10.40.01.jpg 2019-11-17 10.39.52.jpg 2019-11-17 10.39.40.jpg 2019-11-17 10.39.33.jpg



  • @Nxt-1 Wow! looks great. I'm surprised the stepper motor can handled all of that equipment on the one axis.

    Just one question: Why not have the radiator and pump outside? Then you could close up the sides and retain more heat for warp-prone plastics.