Thing-O-Matic: Oozebane Turds

Printing those fairing mounting plates gave me an opportunity to explore the Oozebane parameter space. I wasn’t quite sure how it would work and now I’m certain that it can’t.

Here’s the joint at the start/end of the perimeter extrusion around one of the plates, with Oozebane set for a 4 mm early shutdown:

Perimeter joint - Oozebane
Perimeter joint - Oozebane

You’re looking straight down at three edges (bottom = 2 layers, middle & top = 3 layers), but the shadow obscures the vertical faces; they’re firmly joined. The nozzle enters the picture from the left, slows and stops at the joint, then departs for another location.

The turd appears on the far side of this picture, just above the left hole:

Fairing mount - outside
Fairing mount - outside

Here’s the same joint, but with Oozebane turned off:

Perimeter joint - normal
Perimeter joint - normal

Any questions?

Ah: layer thickness 0.3 mm, w/t=1.7 → width =0.56 mm, 45 mm/s feed, 255 PWM flow.

As nearly as I can tell, Oozebane can’t possibly work the way it’s currently defined, at least for the DC extruder on my Thing-O-Matic. The problem is that Oozebane simultaneously shuts off the extruder and slows the feed rate, but the pressure on the molten plastic inside the extruder continues to force it out at about the same rate for quite some time.

Thus, with the feed rate reduced to some unknown (and unprogrammable) value and the flow continuing at the original rate, each thread endpoint accumulates an oversized turd.

Maybe Oozebane works for somebody else, but a stepper extruder is the right solution…

20 thoughts on “Thing-O-Matic: Oozebane Turds

  1. ed:
    the start-stop points should not line up vertically,they should be like finger joints.

    ps: talk is cheap


    1. There’s a Jitter setting that’s supposed to randomize the endpoints, but I haven’t gotten around to worrying about that…

      Without Oozebane, they’re pretty much a fused joint anyway.

  2. I’ve never gotten Oozebane to do anything useful, and it usually creates a larger mess than when it’s off.

    There used to be DC motor reverse commands (from a “Revese” skeinforge module), but these got removed for some reason. I suspect that with the dodgy motors and/or controllers, it only made things worse (by creating even more EMF glitching).

    My MK5 DC motor is forward-only at this point, because it stopped working directly off the extruder controller board but it does work with a relay. But it really doesn’t matter because the rotation rate is too slow for reversal to really work.

    The MK6 StepStruder seems to have some really fast reversals and re-pressurize motions from what I’ve seen in the videos. I’m on the cusp of purchasing the MK6 upgrade kit because the models I’ve seen pictures of printed with it are really clean (no threads at all).


    P.S. I’ve really enjoyed following your well-thought-out postings.

    1. I tried Oozebane early on with poor results. Now that I’ve puzzled over it for a while, I understand why. Fortunately, nobody will ever notice the edges of those plates on the bike!

      StepStruder seems to have some really fast reversals and re-pressurize motions

      I just finished setting up a combination of Ruttmeister’s Coloso-Gears and ScribbleJ’s filament tensioner with a moderately husky NEMA 17 stepper and it’s a vast improvement over the DC motor. I’m not convinced the additional current required for a direct-drive stepper is a Good Thing, but a geared stepper works fine so far.

      Make sure you apply strong (red) Loctite to the extruder gear setscrew. I’ve had it work loose twice with low-strength (purple) Loctite: the stepper version of Reversal really puts the boots to that gear!

      Thanks for the good words. Although I’m having fun with all this Thing-O-Matic stuff, I’d kind of like it to be over at some point… which point I think is coming up fairly soon. Whew!

      1. >I’m not convinced the additional current required for a direct-drive stepper is a Good Thing,…

        What do you mean by additional current required? If you look at the Calibration page on the wiki, it is being driven with less current than the x and y stepper motors. The motor they are using has a low current rating and is being driven at or under spec.

        1. I take that back, on second glance it is driven with more current than the x and y motors. I still dont understand why a direct drive motor needs “additional current” though. Seems to me if a motor is specially designed to deliver high torque, and it is being driven at its specified current rating, there should be no problems, no?

          1. I must shuffle my notes into order on that thing and do up a formal post, but here’s an overview.

            Assuming the motor is an Anaheim Automation 17Y402S-LW4-01 (by following that comment), then we can find some data there.

            The coil resistance is 12 ohms and the rated current is 850 mA; the coil resistive voltage is 10.2 V and it dissipates 8.7 W standing still. No wonder it needs that cute little fan!

            Coil inductance is 29 mH and the driver has 1.8 V headroom over the resistive drop, so the current changes at 62 A/s (1.8 V / 29 mH). Assuming full-step drive, the current reaches its rated value in 13.7 ms (0.85 mA / 62 A/s), which works out to 73 step/sec. However, the torque depends on the current, so for most of that time the motor delivers far less than its rated torque.

            It normally runs at 2 rev/min, which means 400 step/min, so each step requires 150 ms. The current ramps up 850 mA in the first half of each step, then the driver holds it constant. In round numbers, it’s delivering 75% of rated torque for the entire step.

            However, in order to make the much-touted Reversal ooze control work, the default configuration has it reverse instantly to 35 rev/min = 117 step/sec for a mere 8.6 ms/step.

            With barely 1.8 V to work with (ignoring wiring and driver voltage drops), the current rises to only 530 mA in 8.6 ms: 63% of the rated value. But the average value is half that, so the motor is running at barely 1/3 rated torque.

            Now, the obvious question is how much torque you really need. I can push the filament into the extruder with quite a bit of effort, so let’s assume 10 pounds = 45 N. The filament drive gear has about 9.8 mm effective diameter, so that’s 45 N x 0.005 m = 0.2 Nm.

            The motor’s torque-speed curve at full current shows 75 oz in = 6.3 Nm, so it looks adequate even with the derating due to slow current rise. The torque required during reversal is quite low, so it’ll work for that, too. The folks pushing Reversal to 75 rev/min may be close to the wall, though.

            In contrast, the stepper I’m using gets barely warm while delivering enough torque to the filament through a 7:51 gear train that I can’t stall the motor by pulling backward on the filament. It reverses at 35 rev/min just fine, too. I think that’s a better solution: cheap parts that don’t get hot.

            The writeup slated for tomorrow has a bit more about my geared stepper setup, but doesn’t have the grisly details on torque. I must do more note-beating for that…

          2. I definitely see where you are coming from with the heat issue, and also how it is not the most efficient use of the available torque.

            I look forward to reading your post. It would be great if you talked a little bit about why having so much torque in a geared setup is a good thing. Ever since I have upgraded to the MK6, I have not once stripped the filament because whenever there is a high amount of back pressure the motor will just skip, and I will know to look for something that is not right. I think that is an excellent feature that Makerbot should advertise a little more.

            When I was using the MK4, I actually destroyed the hot end mount at one point from accidentally trying to extrude when the system was not heated up. (required a timely rebuild) The DC motor had so much extra torque beyond what was required to extrude that nothing was going to stand in its way.

            Whether the MK6 is the best solution available or not, I have been printing the best results ever, havent even adjusted anything in skeinforge, and I now have no inhibitions about printing anything. Completely satisfied with my purchase, now I am just hoping it is going to stand the test of time….

            1. whenever there is a high amount of back pressure the motor will just skip

              Now that is an interesting data point!

              I just checked the MK6 setup instructions and the default current setting is about 1.1 A. Now, that’s from a 12 V supply into a motor with 12 ohm coil resistance, so the driver flat-out saturates (it can’t supply 1.1 A) and the motor dissipates 12 W at standstill. No wonder it needs a fan!

              And, at that, it provides less torque than a barely warm NEMA 17 through a gear train.

              Words fail me…

              destroyed the hot end mount at one point

              That’s why I wired the thermal lockout circuit to kill the power, rather than just disconnect the heaters, when it detects an overheated Thermal Core. The MK5 hot end is a lot more robust, but a complete shutdown is the right way to get your attention.

              printing the best results ever

              Absolutely! I have some of the prettiest calibration objects ever! [grin]

              I’d say a stepper extruder lets the TOM print the way it should have from the beginning.

              Well, after a whole bunch of Quality Shop Time devoted to solving other problems, that is…

    1. Just downloaded that one, oddly enough.

      I’ve just finished setting up a geared stepper extruder, so now I’m exploring the Reversal plugin’s oddities… other folks report a slight suckout at the end of the perimeter threads, which I’m also seeing. So many peculiarities!

    1. A random NEMA 17 from eBay, slightly larger than the axis motors and much smaller than the MBI monster. The 7:51 gearing puts plenty of force on the filament while the motor gets just barely warm.

      Maybe it’s just me, but I don’t see the need for for extremely high power motors in a Thing-O-Matic. I do see a definite need for better mechanical and electrical and software design, though.

      Now that it’s running again, though, I have a bunch of stuff that wants to get printed… before improving the filament drive!

      OpenSCAD is now refusing to preview the whole thing

      Looks good here, although there’s the usual announcement about anything even mildly complex:

      WARNING: Normalized tree has 1005 elements!
      WARNING: OpenCSG rendering has been disabled.

      Even with the warning, there’s a pretty 3D structure up there that looks complete and twirls nicely. Whatever’s missing isn’t obvious and what’s there is an impressive design: I like it!

      The doc on that program is so thin…

  3. While I don’t know if they’ve said as much, I suspect the reason MBI went with the monster direct-drive stepper is for the really fast reversal and re-pressurize motions. They sure look fast in the video. A smaller stepper that is geared down just won’t be as fast. How much it matters, I don’t know.

    You sound burned out on the TOM, and that’s sad. I hope you find a way to keep it fun!

    1. I think the “really fast reversal” advantage is somewhat overrated, to put it gently.

      Ruttmeister’s herringbone gears have no significant backlash, so you just reverse the stepper at 51/7 of the speed you want to drive the filament and you’re done.

      A mere 20 rpm seems to work for me, which translates to a whopping 145 rpm at the stepper. That’s on the low end of the torque vs rpm chart: with single stepping, it’s 500 steps/s.

      I haven’t tried to find a speed at which the motor won’t start, but the specs indicate it’ll cold start at 1000 rpm. If reversing at 40 rpm doesn’t do the trick, I’d say there’s something wrong elsewhere.

      But, eh, what do I know?

      find a way to keep it fun!

      Well, I’ve started actually printing stuff, which is certainly a change for the better…

    1. Excellent!

      The original one didn’t work with the current extrusion settings: the bars simply vanished. I was thinking of parameterizing it much as you just did: I’m glad you got there first!


      1. How have you got on with Ruttmeister’s stepper upgrade for the MK5 so far? I’m thinking of printing one for my ToM rather than going for the MBI MK6, I’m trying to find a suitable NEMA 17 stepper at the moment, not as much choice here in the UK.

        1. It’s working fine; tomorrow’s post has some details. After putting the TOM together again, I made a bunch of temperature measurements that were, mmm, distracting.

          I think any random NEMA 17 with about the specs of the axis motors will work fine, because IMO the torque requirements at the extruder have been grossly overstated. Not, of course, that I’ve done any measurements, but … the evidence so far suggests there’s no need to put the boots to the poor thing.

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