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Archive for May 14th, 2011

Thing-O-Matic: Fastest Cephalopods EVAH!

Having printed out a quartet of small octopi in half an hour, I decided to see just exactly how fast this printer can go with its new steppers.

The starting point:

  • Print = 40 mm/s
  • Travel = 60 mm/s
  • Extrude = 2 rpm
  • Thickness = 0.33 mm
  • Width = 0.58 mm = 1.75 w/t
  • First layer = 10 mm/s

Which produced another batch of these cuties:

Small octopus quartet

Small octopus quartet

From here on, though, they’re full sized critters that sprawl over the entire aluminum plate.

Print = 40 mm/s, travel = 100 mm/s, extrude = 2 rpm:

Octopus at 40 mm per sec

Octopus at 40 mm per sec

The numbers scrawled around the tentacles indicate the thickness of the single-layer Skirt extrusion around the outside of the octopus. The platform is high by 0.1 mm in the left rear and low by 0.1 mm in the right front.

Print = 60 mm/s, travel = 100 mm/s, extrude = 3 rpm:

Octopus at 60 and 100 mm per sec

Octopus at 60 and 100 mm per sec

Still low on the back and high in the front, which is comforting. I forgot decided not to adjust that before starting the next part; given my proclivity for hurting myself, that makes sense.

Print = 80 mm/s, travel = 100 mm/s, extrude = 4 rpm:

Octopus at 80 and 100 mm per sec - lost Y steps

Octopus at 80 and 100 mm per sec - lost Y steps

This one failed with at least two cases of Y step loss, giving it a rather rakish, swept-back ‘tude that doesn’t look all that bad on an octopus. The motor was still at 900 mA (REF = 1.8 V), so I goosed it to 1.1 A (REF = 2.2 V) and tried again:

Octopus at 80 and 100 mm per sec - success

Octopus at 80 and 100 mm per sec - success

That one worked perfectly, which just goes to show that diagnostic tests never find the errors that crop up in real life.

So here’s a data point: a Super Stock Thing-O-Matic laying down ABS at 80 mm/s!

As it turns out, the TOM actually prints at top speed only up to about the eyeballs, at which point the Cool plug-in begins slowing things down. I started with a minimum of 15 s/layer, then dropped it to 10 s/layer for the 80 mm/s prints. It still takes about 25 minutes overall, with most of the time devoted to pasting the first layer on the build plate at 10 mm/s.

I didn’t do any optimizing for these prints: I just increased the speeds & flows, then reduced the first layer speed ratio to compensate. I’m sure some tweakage would improve things, but the results look pretty good right out of the box!

In particular, the Reversal plugin is still at 25 rpm, 90 ms in/out, 3 mm threshold, no early action. Those aren’t optimized, but the results seem workable.

The Y axis motor has a winding resistance of 2.2 ohms, so 1.1 A dissipates about 2.7 W. I left the motors continuously energized for about four hours while printing, pausing to make pizza for supper, and printing some more. After an hour at 1.1 A, the Y axis motor was at the high end of “comfortably warm” to the touch and the driver chip was just barely over room temperature. No heatsinks, no fans, no muss, no fuss: the right steppers Just Work.

This is without acceleration limiting, so the X and Y stages must accelerate to full speed in less than two full motor steps. That’s absurd, but that’s how it works right now.

In truth, I think anything over 50-ish mm/s shakes the printer entirely too hard and certainly doesn’t print as precisely, so I don’t plan to run it at those speeds. Except maybe for demos.

Cuing Jan & Dean on Turntable One…

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