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: Science

If you measure something often enough, it becomes science

  • Stone Cold Swerve

    Stone Cold Swerve

    We’re southbound on Rt 376, ticking along at about 15 mph, with fresh string-trimmer debris littering the shoulder:

    T – 50 ms

    Did you notice the rock? I didn’t.

    The fairing ripples as my front tire hits the left side of the rock:

    T = 0

    I have no memory of the next two seconds.

    The offset impact turns the front wheel to the left, so the bike steers out from underneath my weight:

    T + 500 ms

    Because the bike frame was still aimed straight ahead, the wheel is steering further to the left and putting me even more off-balance. I am somehow trying to lean left far enough to get my weight lined up with the bike:

    T + 1.0 s

    One second into the event, Mary has no idea what’s going on behind her.

    My memory resumes with an image of the yellow midline just beyond my left foot:

    T + 2.0 s

    Mary heard an odd sound and asks (over the radio) “Are you all right?”

    I’m approximately balanced, turning toward the shoulder, and manage to shout “NO!”:

    T + 3.0 s

    I’m coasting toward the shoulder with my feet off the pedals:

    T + 4.0 s

    Mary is stopping and I coast past her:

    T + 5.0s

    Landing gear out:

    T + 6.0 s

    Back on the shoulder, lining up with the guide rail:

    T + 7 s

    Dead slow:

    T + 8.0 s

    Docking adapter deployed:

    T + 9.0 s

    And stopped:

    T + 10.0 s

    I sat in that exact position for nearly four minutes.

    A slideshow view of the same images so you can watch it unfold:

    • T – 50 ms
    • T = 0
    • T + 50 ms
    • T + 500 ms
    • T + 1.0 S
    • T + 2.0 s
    • T + 3.0 s
    • T + 4.0 s
    • T + 5.0 s
    • T + 6.0 s
    • T + 7.0 s
    • T + 8.0 s
    • T + 9.0 s
    • T + 10.0 s

    Doesn’t look like much, does it?

    If I could have looked over my shoulder, this is what I would have seen, starting at T = 0 with the rock impact blurring the image:

    • T = 0
    • T + 67 ms
    • T + 1.0 s
    • T + 2.0 s
    • T + 3.0 s
    • T + 4.0 s
    • T + 5.0 s
    • T + 6.0 s
    • T + 7.0 s
    • T + 8.0 s
    • T + 9.0 s

    Surely scared the daylights out of that driver, perhaps confirming all the usual expectations of crazy bicyclist behavior.

    Here’s what Mary would have seen over her shoulder, again starting at T = 0 with the fairing bulging from the impact:

    • T = 0
    • T + 467 ms
    • T + 833 ms
    • T + 1.0 s
    • T + 2.0 s
    • T + 3.0 s
    • T + 4.0 s
    • T + 5.0 s
    • T + 6.0 s
    • T + 7.0 s

    Timing is everything.

    That Benz is new enough to have automatic emergency braking, as it slowed pretty dramatically while I was busy getting out of the way, but it’s not clear whether AEB knows about small / lightweight targets like pedestrians and bicyclists.

    We completed the ride as planned, although I finally realized the front fender bracket had broken a few miles later.

    Every adult human male has at least one story beginning “But for that millisecond or inch, I wouldn’t be here.” Now I have one more.

    I must not fear. Fear is the mind-killer. Fear is the little-death that brings total obliteration. I will face my fear. I will permit it to pass over me and through me. And when it has gone past I will turn the inner eye to see its path. Where the fear has gone there will be nothing. Only I will remain.

    Frank Herbert, Dune
  • Tree Frog Season

    Tree Frog Season

    This year brings an abundance of tree frogs:

    Tree frog - on dahlia stem
    Tree frog – on dahlia stem

    Despite the snappy green color, they’re Gray Treefrogs:

    Tree frog - on patio step
    Tree frog – on patio step

    Their camouflage works better in the wild than atop a trash can lid:

    Tree frog - on trash can lid
    Tree frog – on trash can lid

    They are much smaller than you’d expect from their voices in the night:

    Tree frog - on trash can lid - thumb for scale
    Tree frog – on trash can lid – thumb for scale

    We think the drought brings them closer to the house in search of water, as Mary collects rainwater in the trash cans where the frogs easily walk up & down the inside surfaces.

  • OMTech 60 W Laser: Replacement HV Power Supply Waveforms

    OMTech 60 W Laser: Replacement HV Power Supply Waveforms

    While I had the hatch open, I thought it would be interesting to look at the HV supply’s current waveforms:

    HV laser power supply - current probe setup
    HV laser power supply – current probe setup

    The Tek current probe over on the right measures return current through the cathode wire, the point in the circuit where you might be tempted to install an ordinary analog (moving-coil) panel milliammeter, oriented so (conventional) current returning from the tube will produce a positive voltage.

    Unfortunately, an analog meter isn’t up to displaying anything meaningful for this nonsense:

    HV laser power supply - 5 mA-div - 50 ms 10 pct pulse
    HV laser power supply – 5 mA-div – 50 ms 10 pct pulse

    Admittedly, that’s a 50 ms pulse, during which an analog meter would barely twitch. The vertical scale is 5 mA/div, so the highest peaks exceed 35 mA, more than twice the tube’s recommended “14-15 mA”.

    A closer look at the pulse startup waveform:

    HV laser power supply - 5 mA-div - 50 ms 10 pct pulse - detail
    HV laser power supply – 5 mA-div – 50 ms 10 pct pulse – detail

    It sure looks like the chaotic current through a forced neon-bulb relaxation oscillator. Remember neon bulbs?

    An even closer look:

    HV laser power supply - 5 mA-div - 50 ms 10 pct pulse - tight detail
    HV laser power supply – 5 mA-div – 50 ms 10 pct pulse – tight detail

    That’s at 10% PWM, close to the threshold below which the laser just won’t fire at all. The power supply must ramp up to produce enough voltage to fire the tube while simultaneously limiting the current to prevent the discharge from sliding down the negative resistance part of its curve.

    Apparently this supply isn’t quite up to the task.

    A 10 ms pulse at 50% PWM gives the supply enough time to stabilize the current:

    HV laser power supply - 5 mA-div - 10 ms 50 pct pulse
    HV laser power supply – 5 mA-div – 10 ms 50 pct pulse

    The 14-ish mA at the tail end of the pulse (note the baseline offset) matches my previous 13 to 14 mA measurements as closely as seems reasonable. That 2 ms of hash on the leading edge suggests the start of each cut or engraving line will be a bit darker than you might expect.

    Another 10 ms pulse, this time at 99% PWM:

    HV laser power supply - 5 mA-div - 10 ms 99 pct pulse
    HV laser power supply – 5 mA-div – 10 ms 99 pct pulse

    The peak 24-ish mA matches the previous measurements. Note that the peaks in all the previous pictures exceed the 99% PWM current level.

    AFAICT, all PWM values below about 25% produce equivalent results: random current spikes with unpredictable timing and amplitude. Changing the PWM value does not affect the (average) tube current or laser output power in any predictable way.

    Some samples to illustrate the point, starting with a different 50 ms pulse at 10% PWM than the first one up above:

    HV laser power supply – 5 mA-div – 50 ms 10 pct

    A 50 ms pulse at 15% PWM:

    HV laser power supply - 5 mA-div - 50 ms 15 pct
    HV laser power supply – 5 mA-div – 50 ms 15 pct

    A 50 ms pulse at 20% PWM:

    HV laser power supply - 5 mA-div - 50 ms 20 pct
    HV laser power supply – 5 mA-div – 50 ms 20 pct

    A 50 ms pulse at 25% PWM:

    HV laser power supply - 5 mA-div - 50 ms 25 pct
    HV laser power supply – 5 mA-div – 50 ms 25 pct

    Now, that last one is different. After the hash during the first 8 ms or so, the power supply actually produces a stable 5 mA beam current, which is roughly what I measured using the power supply’s meter.

    However, the other three are pretty much identical: the 10% PWM pulse does not delivers half as energy as the 20% PWM pulse. The waveforms may be different, but not in a meaningful or consistent way: the two 50 ms 10% pulses are different, but you’d (well, I’d) have trouble separating them from the 20% pulse.

    To summarize:

    • The first several millisconds of any pulse will consist of randomly distributed spikes with very large tube currents.
    • For PWM values greater than 25%, the tube current will settle down to the corresponding current after 5 to 10 ms. Before the current settles down, the tube will be firing those random spikes.
    • For PWM values less than 25%, the tube current never settles down: the entire pulse, no matter how long, will be short, high-intensity spikes, without a consistent DC-ish level.

    No matter what an analog meter might show.

    I have no way to know if this power supply is defective, but I’ll certainly ask …

  • Smashed Glass vs. Epoxy

    Smashed Glass vs. Epoxy

    Just to see what happens, I laid some smashed glass in puddles of epoxy:

    Smashed Glass vs epoxy - samples
    Smashed Glass vs epoxy – samples

    Backlighting with the LED light pad reveals more detail:

    Smashed Glass vs epoxy - backlit samples
    Smashed Glass vs epoxy – backlit samples

    The chunk on the left is the proof-of-concept shot glass coaster with a form-fit black acrylic mask atop a clear epoxy layer on a clear acrylic base. The chunk at the top is raw shattered glass fresh from the pile. The two chunks on teardrop acrylic scraps are bedded in transparent black and opaque black tinted epoxy.

    A look through the microscope at all four, laid out in that order, with the contrast blown out to emphasize the grain boundaries:

    Smashed Glass vs epoxy - magnified comparison
    Smashed Glass vs epoxy – magnified comparison

    You may want to open the image in a new tab for more detail.

    The raw chunk has air between all its cuboids, so it’s nicely glittery. All the others have much of their air replaced by epoxy.

    Clear epoxy produces an essentially transparent layer where it fills the gaps, because its refractive index comes close enough to the glass. The stretched contrast makes the gaps visible again, but the backlit image shows the unassisted eyeball view.

    Transparent black dye sounds like an oxymoron, but it fills the gaps with enough contrast to remain visible. The overall chunk is not particularly glittery, but it’s OK.

    Opaque black dye produces a much darker tint; the slightly tapered thin layer between the glass and acrylic (the small white circles are air bubbles) cuts down on the transmitted light. The gaps remain nearly as prominent as in the air-filled chunk, although with very little glitter.

    Bedding the glass in epoxy against an acrylic sheet should reduce its tendency to fall apart at the slightest provocation, although the proof-of-concept poured coaster showed the epoxy must cover the entire edge of the glass sheet to bond all the slivers in place.

  • Onion Maggot Flies vs. Sticky Traps: Round 2

    Onion Maggot Flies vs. Sticky Traps: Round 2

    Mary decided the second round of sticky traps had collected enough Onion Maggot Flies (and other detritus) to warrant replacement, so this season will have three sets of cards.

    The two sides of each card after about a month in the garden:

    • VCCG Onion Card A - 2022-07-17
      VCCG Onion Card A – 2022-07-17
    • VCCG Onion Card B - 2022-07-17
      VCCG Onion Card B – 2022-07-17
    • VCCG Onion Card C - 2022-07-17
      VCCG Onion Card C – 2022-07-17
    • VCCG Onion Card D - 2022-07-17
      VCCG Onion Card D – 2022-07-17
    • VCCG Onion Card E - 2022-07-17
      VCCG Onion Card E – 2022-07-17
    • VCCG Onion Card F - 2022-07-17
      VCCG Onion Card F – 2022-07-17

    There are many flies that look (to me) like Onion Maggot Flies, in contrast with the first round of cards which had far fewer flies after about six weeks in the bed.

    Some could be Cabbage Maggot Flies, but my fly ID hand is weak.

    One of the frames screwed to a fence post suffered a non-fatal mishap, so I made and deployed a seventh trap. We’re pretty sure the garden has enough flies to go around.

  • Lawn Chair Re-strapping: Countdown Hold

    Lawn Chair Re-strapping: Countdown Hold

    I planned to replace the vinyl straps on our set of (salvaged) lawn / patio chairs and made a pair of rivets for one long-missing strap:

    Lawn chair strap rivets
    Lawn chair strap rivets

    The overall project is on indefinite hold, as a Steel-blue Cricket Hunter (*) has decided at least one of the chairs is an ideal place to start a family:

    Lawn chair - wasp nest under construction
    Lawn chair – wasp nest under construction

    The patio under the chair is littered with blades of grass and twigs that didn’t quite fit through the 5 mm vent hole in the tube, but that long stem went in just fine:

    Lawn chair - wasp nest grass stem
    Lawn chair – wasp nest grass stem

    We have seen the wasp airlifting crickets near the chair, so provisioning has begun. The cricket seemed not only larger than the hole, but also larger than the wasp; we assume the wasp knows what she’s doing.

    The new wasp will hatch this year, pupate over the winter, then hatch and emerge next summer, but I plan to replace the straps after the construction season ends.

    I have no idea how to clean out whatever’s accumulating in there …

    (*) I learned them as Steel-blue Cricket Killer, but the crickets are just paralyzed, not completely dead.

  • Gentec ED-200 Absorber Surface Damage

    Gentec ED-200 Absorber Surface Damage

    Having grossly exceeded the Gentec ED-200 maximum power spec, I wasn’t surprised to see this when I finally tucked it back in the drawer:

    Gentec ED-200 surface damage
    Gentec ED-200 surface damage

    The 0.5 mm scale suggests the damage came from a defocused 2 mm beam or the hot central part of a larger beam, but I obviously wasn’t paying enough attention at the time.

    The rest of the surface seems undamaged, so this may have been one of those inadvertent long-duration pulses or several shorter shots in one spot.