Fighting with computers

Computers are not always friendly.

Tuesday, August 05, 2014

More on delta 3D printers

It's been quite busy around here lately. Still, I have managed to build a couple of delta 3D printers with heated beds and develop a couple of ideas that seemed worth trying.

One of these ideas is the use of a heated bed. While I can see that some people are moving away from ABS to use just PLA plastic, I do not see how I can use a PLA-only solutions for environments where temperature can be high, like inside of a car or near a hotend or heated bed.

Two different types of extrusions and carriages were tested: wheeled carriages over the extrusion resulted in a quieter and more accurate system than rails. But the IGUS guides used had quite play by design. After watching the videos of them working I am not sure they are a good choice for this particular use, though printed parts do not look bad after all.

While Johan pioneered the use of force sensing resistors on the bed for probe-less bed detection, I was not pleased with the additional cost these FSR sensors would add, so I turned to the same idea Brook did with the metal Printrbot Simple: the use of inductive proximity detectors (as I am using aluminum heated beds). As I wanted to add the sensor to the effector and to use magnetic couplings instead of Traxxas ball joints, I designed a few new parts.

I am very happy with these plastic parts for creating a Kossel Mini using 2020 extrusions. And the guys from Mecaduino provided me a set of parts for making a Kossel Mini using their metal parts (however I did print some plastic parts to use magnetic coupling and inductive proximity probe with it too.

With the magnetic couplings, with I liked more than ball joints, as they have zero slop, if you set the acceleration too high (in my case higher than 1500mm/s^2) the rods will fall apart on any fast movement, that will never happen with a ball joint. I am using 10mm steel balls and 6mm-diameter 8mm-long N35 magnets. I guess stronger magnets will allow you higher effective accelerations.

The second innovation I have been testing is the auto-calibration firmware I mentioned in a previous post by Rich Catell. While the first time I used in a 3DR printer with a mechanical switch the firmware converged quickly, these two other printers gave me hell and did not converge to a valid calibration all the time. Maybe part of the problem was due to not so accurate build of these deltas but another reason could be associated with the way measurements are performed. Once I switched to the median filter code by Brad Hopper the results of auto-calibration improved notably on both printers. 

Now it seems I am getting good prints from both printers and start to feel a bit more confident about this type of printer, so I guess I am venturing in a new type quite soon: Ingentis/Eustathios are next.


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