The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Category: Oddities

Who’d’a thunk it?

  • Independence Day 2011

    From our Declaration of Independence:

    We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness. That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness. Prudence, indeed, will dictate that Governments long established should not be changed for light and transient causes; and accordingly all experience hath shewn, that mankind are more disposed to suffer, while evils are sufferable, than to right themselves by abolishing the forms to which they are accustomed. But when a long train of abuses and usurpations, pursuing invariably the same Object evinces a design to reduce them under absolute Despotism, it is their right, it is their duty, to throw off such Government, and to provide new Guards for their future security.

    We read the original document in DC a few months ago, while doing the touristy thing. These days, that means submitting to a search on the way into each museum; Mary lost her forgotten-in-the-bottom-of-her-purse Swiss Army Knife to the Smithsonian guards.

    We left town feeling that something has gone badly wrong in the last decade or so.

  • Personal Protective Equipment: Start ‘Em Young!

    That comment prompted me to rummage around for one of my favorite photos: a much younger version of my Shop Assistant helping us shred leaves in the front yard.

    Shop Assistant in Autumn leaf pile
    Shop Assistant in Autumn leaf pile

    She thinks it’s entirely right & proper to:

    • don safety goggles while doing anything even remotely eye-unsafe
    • wear a dust mask to mow the lawn
    • jam 30 dB foam plugs into her ears during thrash metal concerts

    A parent can’t ask for more, methinks…

  • Thing-O-Matic: Large Knots

    Printing tiny knots showed the need for support under the loop takeoff points, which xorxo’s Hi-Res 3D Knot provides:

    Large Knot - scaffolded
    Large Knot – scaffolded

    My Shop Assistant cleaned up a second version:

    Large Knot cleaned - top
    Large Knot cleaned – top

    As the scrawled notation says: printed at 50 mm/s with 100 mm/s moves. The only cleanup: remove the scaffolding and slice off the Reversal zittage.

    If the truth be known, that was actually the third knot. The first suffered a spectacular failure: one corner of the filament spool snagged on the wall behind the printer and jammed the filament:

    Large Knot - failed
    Large Knot – failed

    The filament drive pulled all the slack out of the bundle, broke off three of the six internal guide posts (admittedly, they’re just hot-melt glued in place), and dragged a nasty kink halfway down the feeder tube. Obviously the stepper was shedding steps during that whole process, but it came rather close to doing the Ouroboros thing.

    While that went down, I was puttering around in the far reaches of the Basement Laboratory, attempting to clean up a bit of the clutter, and checking in on the printer every now and again. Seemed like a good idea at the time, is all I can say.

    Perhaps the Lords of Cosmic Jest simply decided this was an appropriate object to mess with. The vertices of the hexagonal filament spool stick out perhaps 10 mm from the printer’s backside and every one has cleared the wall on countless previous rotations. I moved the entire affair a bit further from the wall and maybe it’ll be all good from now on.

  • Stepper Motor Driver Bypassing: Mind the Voltage

    The supply voltage for that picture came from a bench supply and, having confirmed that the initial slope of the current waveform matched the voltage, I twiddled the knob while watching the slope change.

    As expected, lower voltage = lower slope and higher voltage = higher slope. That worked fine, right up until a firecracker popped about a foot in front of my face, launched a missile over my left shoulder, and filled the Basement Laboratory with the pungent smell of electrical death.

    Detonated electrolytic cap
    Detonated electrolytic cap

    While wiring up a hairball test circuit for that Pololu driver, I’d put a pair of electrolytic caps on the +5 and +12 V supply lines, seeing as how solderless breadboards aren’t all that great for power distribution. The brown fur growing just to the upper right of the heatsink is what’s left of a 16 V cap that had 25 V applied for a few seconds: I’d wired in the bench supply in place of the breadboard’s fixed +12 V output and forgot all about the caps.

    The cap body departed for the far reaches of the Basement Laboratory, leaving behind shredded cardboard and unrolled plastic strips. I’m sure it’ll turn up some day.

    Nothing else took any damage, but for a few minutes I thought I’d killed Eks’ AM503 current probe, which pokes in from the lower right.

    The black lump just above the probe is an ordinary AC current transformer that didn’t work well at all: the 1/rev frequency was just too low.

    If you don’t always wear glasses at the workbench, start now.

  • Bedbugs Redux

    Mary quite deliberately brought home a pair of bedbugs… even knowing what we went through, you cannot imagine how dead those things had to be. She doesn’t just want them dead, she wants them extinct.

    Anyhow.

    Some pix, atop a scale with 0.5 mm divisions:

    Bedbug - 4 mm - dorsal
    Bedbug – 4 mm – dorsal
    Bedbug - 4 mm - ventral
    Bedbug – 4 mm – ventral
    Bedbug - 6 mm - dorsal
    Bedbug – 6 mm – dorsal
    Bedbug - 6 mm - ventral
    Bedbug – 6 mm – ventral
    Bedbug - 6 mm - mouthparts
    Bedbug – 6 mm – mouthparts

    They were actually on load from Cornell’s Co-op lab, having recently been distinguished from bat bugs.

  • Gas Grill Igniter: Design Failure Therein

    The Judges at the Trinity College Home Firefighting Robot contest use butane grill igniters to light the candles in the arenas, but the gadgets seem to have terrible reliability problems: very often, they simply don’t work. I brought a few deaders back to the Basement Laboratory this April and finally got around to tearing them apart.

    It seems they don’t ignite because the trigger’s safety interlock mechanism shears the plastic gas hose against the fuel tank’s brass outlet tube:

    Grill igniter with sheared gas tube
    Grill igniter with sheared gas tube

    I tried putting a small brass tube around the (shortened and re-seated) hose, but it turns out the trigger interlock slides into that space and depends on the hose bending out of the way:

    Grill igniter with brass tubing
    Grill igniter with brass tubing

    So there’s no easy way to fix these things.

    It seems to me that a device using flammable gas should not abrade its gas hose, but what do I know?

  • OPB815 Optical Switch: Always Measure Your Components

    Given this ID printed on the side of an old OPB815 optical interrupter switch:

    OPB815 Optical Interrupter Switch - detail
    OPB815 Optical Interrupter Switch – detail

    And this pinout diagram from a randomly chosen datasheet for that part number:

    OPB815 Datasheet Pinout Diagram
    OPB815 Datasheet Pinout Diagram

    One might reasonably be led to believe that the white dot on the part marks the LED anode. That’s what I thought, too, but the innards are actually rotated 180° from the picture: the dot marks the transistor collector.

    Took me a while to figure that out; I eventually tore one apart and used my pocket camera to look for the blue-white glare of the IR emitter.

    After the dust settled, I rummaged around in the impacted shitpile holding my paper documents and found the original 1982 datasheet, with my very own scrawled notes:

    Original OPB815 Datasheet Pinout Diagram
    Original OPB815 Datasheet Pinout Diagram

    Back in the day, the dot on pin 1 marked the transistor collector…

    Memo to Self: No, scanning all that old paper wouldn’t help.