BLtouch on Polar kinematics and some questions



  • Hi all, I'm currently doing a Circa V2 Polar 3D printer that as the name says, runs on Polar co-ordinates, as I feel like it'll be much "cooler" to watch then the two cartesian type the schools has for my students for them doing 3D designing. I just have some questions before I make the splurge and buy the Duet Maestro for it, if that is okay.

    1. Unfortunately for me, the bed isn't leveled with the Nozzle and varies wildly up to 0.6mm from one side to another, and since Polar beds are hard to level manually (at least to my knowledge and this printer's design), I did some drilling and managed to fit a BLtouch (will be putting in a genuine one, just using this one as a temporary) in there.

    For the X and Y offsets, now I'm not concerned so much as for the X offset, as that is the Radius motor so it's straight in line, but my Bl touch is not mount straight to the nozzle, as you'll see in the picture, there is Y offset (the turntable). So while the X offset seems straightforward to measure, is it true also for the Y offset? Or is there some other measurement method I have to use to measure the Y offset? Or is it the same as any other kinematics, just measure and input it in?

    1. I realize that for some polar machines, they cannot print on position 0,0 due to kinematics, does the Duet has this problem too or no it can print moves around 0,0 or on it perfectly fine?

    2. For the slicer, will any slicer do as long as I make it into circular bed like a delta and choose relative movement or are there only certain slicers that can make it work?

    I've included some pictures to hopefully better demonstrate what I mean, as I'm usually really bad a saying what I want to say in words/texts.

    https://www.dropbox.com/s/6wy7tib7dlla4b5/2019-11-09 22.07.35.jpg?dl=0
    https://www.dropbox.com/s/23f13b5t74vpqja/2019-11-09 22.07.41.jpg?dl=0
    https://www.dropbox.com/s/h5qe1fs5uymgwl6/2019-11-09 22.07.53.jpg?dl=0
    https://www.dropbox.com/s/occ5xww9sjx4t7n/2019-11-09 22.07.59.jpg?dl=0
    https://www.dropbox.com/s/36a2v61c8cc5nyb/2019-11-09 22.08.16.jpg?dl=0

    Thank you very much!!

    Small Update: I also see that my nozzle isn't exactly in the middle of the bed, is that a fail and this build is bust? It's a little like 0.5mm off to the left as you can see in these pictures below. man Polar printers can have less mechanical parts, but the amount of work >.<

    https://www.dropbox.com/s/tluk55ce1bq1ake/2019-11-09 22.46.07.jpg?dl=0
    https://www.dropbox.com/s/gfjbx2z0myvgps7/2019-11-09 22.46.09.jpg?dl=0



  • @iamthebest22 I have some thoughts about your questions. I cannot answer all your questions, but here are my ideas:

    • Your 0.5 mm offset to the middle should be corrected, as there is no offset configuration possibility in the provided Marlin code of the Circa project, and there is no offset option in the Duet firmware also. (BTW It would be easy to change the Duet firmware to add a configuration option for it, but someone has to do and support it.)
    • printing in the center: there is an interesting comment by user unlimitedbacon in the thread https://reprap.org/forum/read.php?185,178379,206119 which explains it very good IMHO in his comment on May 06, 2013 06:44PM which begins with "The speed issue is an interesting question."

  • administrators

    @iamthebest22 said in BLtouch on Polar kinematics and some questions:

    1. Unfortunately for me, the bed isn't leveled with the Nozzle and varies wildly up to 0.6mm from one side to another, and since Polar beds are hard to level manually (at least to my knowledge and this printer's design), I did some drilling and managed to fit a BLtouch (will be putting in a genuine one, just using this one as a temporary) in there.

    For the X and Y offsets, now I'm not concerned so much as for the X offset, as that is the Radius motor so it's straight in line, but my Bl touch is not mount straight to the nozzle, as you'll see in the picture, there is Y offset (the turntable). So while the X offset seems straightforward to measure, is it true also for the Y offset? Or is there some other measurement method I have to use to measure the Y offset? Or is it the same as any other kinematics, just measure and input it in?

    I can't see any reason why you can't just measure the Y offset and enter it in your G31 command n the usual way.

    Note, if you don't have a homing switch for the turntable (i.e. it starts in a random position), then you will need to probe the bed at the start of each print, and not home the printer between bed probing and printing. OTOH if you do provide a turntable homing switch, then you should be able to save and recall height maps, avoiding the need to probe the bed each time.

    1. I realize that for some polar machines, they cannot print on position 0,0 due to kinematics, does the Duet has this problem too or no it can print moves around 0,0 or on it perfectly fine?

    All polar printer have a problem at the origin, because the turntable position is indeterminate there and crossing the origin requires a rapid movement of the turntable. I've never built a polar printer, but RepRapFirmware on the Duet should be able to cross the origin. However, the large turntable movements as you cross the origin will slow down movement to keep the speed and acceleration within limits, so print quality will be poor around the origin. Therefore I suggest you avoid printing at or close to the origin.

    1. For the slicer, will any slicer do as long as I make it into circular bed like a delta and choose relative movement or are there only certain slicers that can make it work?

    Any slicer should do.

    Small Update: I also see that my nozzle isn't exactly in the middle of the bed, is that a fail and this build is bust? It's a little like 0.5mm off to the left as you can see in these pictures below. man Polar printers can have less mechanical parts, but the amount of work >.<

    https://www.dropbox.com/s/tluk55ce1bq1ake/2019-11-09 22.46.07.jpg?dl=0
    https://www.dropbox.com/s/gfjbx2z0myvgps7/2019-11-09 22.46.09.jpg?dl=0

    RepRapFirmware doesn't yet have a parameter to allow for that, but it could be added. Of course, such an offset will make it impossible to print within 0.5mm of the origin.



  • Okay that is great to hear that there is no special measurement needed for the Y offset phew.

    Ah I see, well it's meant to be a fun experiment for my elementary students, it's never going to print anything high quality or precision, so I'm okay with it, as long as it can print at in the middle.

    Interesting enough, I just found out it's not the mechanical parts that's offset in the middle, it's the nozzle I'm using (it's a cheap clone I'm also temporary using), it's just so slightly off due to the cheap hotend block. After a little hammering and twisting, it's not pretty much on point (like 0.1mm at most). Worse comes to worse, I can just add a very small hole int he middle of everything I build right? xD

    Okay I will purchase the Maestro and get started, I can continue to post any problems or questions I have in this thread, if that's alright?



  • @iamthebest22 If financially possible, I would prefer Duet 2 (Wifi or Ethernet) to the Maestro, because Duet 2 has an FPU and to my knowledge Maestro doesn't have it. The Polar kinematics uses tan, sin and cos functions to calculate the positions. Maybe @dc42 can tell whether this matters in respect to timing/stepper speeds.


  • administrators

    @JoergS5 said in BLtouch on Polar kinematics and some questions:

    @iamthebest22 If financially possible, I would prefer Duet 2 (Wifi or Ethernet) to the Maestro, because Duet 2 has an FPU and to my knowledge Maestro doesn't have it. The Polar kinematics uses tan, sin and cos functions to calculate the positions. Maybe @dc42 can tell whether this matters in respect to timing/stepper speeds.

    That's correct, the Duet Wifi or Ethernet can do the trig calculations much faster. In fact there is a special M-code (M122 P103) to time how long sine and cosine calculations take. I've just run it, and here are the results:

    Duet 3: single precision 6.55us, double precision 12.07us
    Duet WiFi/Ethernet: single precision, 2.14us ok, double precision 50.68us
    Duet Maestro: single precision 31.83us, double precision 50.17us

    Duet 3 is running with cache memory disabled at present, it should get a lot faster when we enable the cache. RRF uses almost exclusively single precision maths, so it is the single precision speed that matters.



  • Oomph if you only had just posted a few hours earlier >.< I already purchased the Duet Maestro >.<. Maybe in the future, right now I only plan on printing at like 30-40mm/s at most on this polar machine, so I think the Duet Maestro will be fine at that speeds for now? Or would the Duet Ethernet be a really much better choice? (Ethernet version because I have a 32 network switch in my 3d printer room so all my printers are on ethernet, except the ones running the duet wifi's) I can possibly cancel the order and get the duet ethernet cheaper (cause I got a discount).



  • Question, my Duet Maestro is on it's way, I'm using the reprapfirmware online configurator, and I don't see the Polar as an option under Printer Geometry, do I temporary select Cartesian, and then later change the movement section under config.g as mentioned here?

    https://duet3d.dozuki.com/Wiki/ConfiguringRepRapFirmwarePolarPrinter

    Thanks


  • administrators

    @iamthebest22 said in BLtouch on Polar kinematics and some questions:

    Question, my Duet Maestro is on it's way, I'm using the reprapfirmware online configurator, and I don't see the Polar as an option under Printer Geometry, do I temporary select Cartesian, and then later change the movement section under config.g as mentioned here?

    https://duet3d.dozuki.com/Wiki/ConfiguringRepRapFirmwarePolarPrinter

    Thanks

    Yes. When assigning motor parameters and endstop inputs, treat the radial arm as X and the turntable as Y.



  • Thanks, got the config sorta setup via configuration tool, just need to change the movement to polar and will post it here soon to confirm before my Duet Maestro arrives.

    First thing, about the Bltouch offset, is it similar to Marlin (if that's okay to say here), so as you can see in the pic, the BLtouch is to the right and front of the Nozzle (you can see the homing switch for the X in the back also, that's the X maximum Radius, NO minimum X radius homing switch). So that means the offset if similar to the Marlin, should be -17.5mm for Y and for X should be +22.5mm? Is that correct?

    Pics:
    https://www.dropbox.com/s/is500e0kb6gc5kl/2019-11-15 23.39.37.jpg?dl=0

    2019-11-15 23.39.54.jpg


  • administrators

    @iamthebest22 said in BLtouch on Polar kinematics and some questions:

    the BLtouch is to the right and front of the Nozzle (you can see the homing switch for the X in the back also, that's the X maximum Radius, NO minimum X radius homing switch). So that means the offset if similar to the Marlin, should be -17.5mm for Y and for X should be +22.5mm? Is that correct?

    If in Cartesian coordinates +X is to the right and +Y is to the rear, that's correct.



  • wait I just realized, if the radial arm is the X and turntable is Y, shouldn't what I said before be flipped? the X be -17.5mm and Y be 22.5mm?



  • I just changed the config.g and the homeall, homez, homeradius, homebed, I've post it up here, I'm wondering these are correct? Thanks.homez.g homeradius.g homebed.g homeall.g config.g


Log in to reply