Triangular notches in the support arms – why?

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    • #5927
      JeffRodriguez
      Participant

      I noticed these notches cut into the bottom of the support arm and I was wondering why they exist. My printer’s a bit misaligned and the split is having problems with adhesion.

      View post on imgur.com

    • #5929
      JeffRodriguez
      Participant

      Update: I disabled those notches in my local copy and printing went much more smoothly.

      Still curious why the notches are there 🙂

    • #5931
      Quentin Harley
      Keymaster

      The notches are there to help you measure your exact arm length. Because the SCARA inverse kinematic transform relies heavily on the accuracy of the arm length, you have to get it as accurate as possible.

      Problems here will cause scale issues when printing.

    • #5939
      MacMarty15221
      Participant

      Speaking of those notches….

      I was looking at the Configuration.h file today, and I noticed that the inner arm length and outer arm length are established right there at the top. It set me to wondering – If I wanted to have a larger build platform, would it be as simple as building appropriate arms (say, 200mm), changing the parameters, and recompiling the firmware? My hopeful self is encouraged, but my cynical brain, scorched by long experience, bets otherwise. (Optimistic self also wants to paint 3m by 3m pictures in the street using the SCARA mechanism.)

    • #5941
      Quentin Harley
      Keymaster

      Your optimistic self is right. You could make the arms as long as you want, but remember that longer arms will have lower resolution if you do not scale the drive wheels accordingly.

    • #5944
      Eujean
      Participant

      On this thought (Imagining a garage size Morgan Cheetah offspring) won’t the longer arms cause the load to be furthest away from the drive shaft causing sag?

    • #5945
      Quentin Harley
      Keymaster

      Yes, it could. This is not a problem though. The bed level code will compensate for any sag.

      Of course you will have to make some material choices to limit sag as much as possible.

    • #5946
      JeffRodriguez
      Participant

      Quentin, I’ve been working on my own Morgan clone based on your design. First off, a lot of the engineering decisions you’ve made become obvious when you dig into the design.I can see there’s a lot of thought and work in the Morgan, so congrats and thank you for your efforts.

      Q1: What made you decide to install the Psi arm on the threaded rod instead of the tube? It seems like the tube would better support the weight of the print head and reduce sagging.

      Q2: I’m planning to replace the upper tube bearing with three 608 bearings to simplify the BOM. Thoughts?

      Q3: I’m also working on replacing the print head bearing with a single 608 and moving the print head to the side of the outer Psi arm (perpendicular). I haven’t dug into the interpolation code yet, but I’d like to think 90deg and an offset wouldn’t be too big a deal. If it works, a second print head might not be too far off.

      Q4: I’m also working on replacing the smooth rods with angle iron, which I intend to use as two legs of a 3-legged table (ditching the PVC and associated feet). Are there any problems with that approach that you can see?

      Thanks again!

    • #5947
      Quentin Harley
      Keymaster

      Thanks!

      A1: Mostly arm placement. I have been working on a new set of arms that will be anchored on the pipe for stability, will post photos of it by next week.

      A2: Interesting… How?

      A3: You can make it work by just making the opposing arm proportionally shorter as well. This will keep the code the same.

      A4: The current triangular frame gives it the stability in that the frame is under stress. Removing the stress and triangles will introduce wobble. Wobble brings unwanted artifacts. Your job would be to combat those.

      Best of luck on the build! Pictures mandatory…

      Q

    • #5948
      JeffRodriguez
      Participant

      2: Like a lathe steady rest:

      3: Thanks. I’m not quite there yet, hopefully this week. I’ve been dealing with printer issues and finally have a set of decent drive wheels.

      4: That’s what I kinda figured. I’m gonna have to get creative and see if I can stabilize with less hardware. Have you considered guy-wires?

    • #5949
      Quentin Harley
      Keymaster

      2: Does the bearings ride on the pipe, or is the bracket attached to the pipe and the bearings run inside a hole?

      If the former, you will just need to ensure your pipe is perfectly round to prevent inaccuracies.

      4: I did try them initially, but they stretched, and I kept having to adjust. The triangular config followed, so I cannot say if I gave it enough time. Perhaps if you use pre stretched wire it should be good.

    • #5950
      JeffRodriguez
      Participant

      2: I was planning on a direct pipe/bearing interface so that’s good to know. I’ve got some 3/4″ round welded steel tubing. I wouldn’t say it’s “perfect” 19.04-19.25mm. So let’s see, that’s 0.21mm out of round on the diameter, or 0.105mm on the radius.

      4. I figured you might have 😉 Good to know. That does get me noodling on what materials might be good guy-wires and a good way to tension them. It would be *really* slick if I could use the same material for guy-wires and line-drive, e.g. spectra.

    • #5951
      Quentin Harley
      Keymaster

      You could stick the pipe in a lathe, and just make that section round…

    • #5960
      JeffRodriguez
      Participant

      Here’s an update Quentin!

    • #5971
      Quentin Harley
      Keymaster

      Looking good so far!

    • #5979
      JeffRodriguez
      Participant

      Hi Quentin, brain pickings again 🙂

      Here’s a new idea for the frame and table:

      View post on imgur.com

      View post on imgur.com

      Did you ever explore this corner-style format?

      One more with 225mm arms and a 300mm build plate:

      View post on imgur.com

    • #6033
      Quentin Harley
      Keymaster

      Nothing wrong, except that you need to cut a notch in the cornet for the wheels to stick through. Your wheels are too small to have a decent resolution on head movement. Other than that it seems good.

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