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?

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

My Shop Assistant cleaned up a second version:

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

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.

2011-06-23
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

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.

2011-06-21
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 – ventral

Bedbug – 6 mm – dorsal

Bedbug – 6 mm – ventral

Bedbug – 6 mm – mouthparts

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

2011-06-19
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

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

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?

2011-06-18
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

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

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

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.

2011-06-12
Architectural Forethought: Lack Thereof

Plumbing trim plate vs tiled wall

This from a restroom near the new high school auditorium, rebuilt at vast expense over the course of several years. You’d think for all the big bucks, somebody would remember that trim plates require a flat surface.

It’s not like I’ve never forgotten a detail in any of my designs. In this case, though, several different people surely noticed this situation and none of them were sufficiently empowered to fix the problem.

I’ve got a ten cent bet with myself that this will never get repaired. I’ll likely never know, though, as my Shop Assistant graduates this year.

2011-05-24
Mysterious Warning Glyphs
Found this on the hand-cranked reel that deployed an outdoor table umbrella in DC…

Table Umbrella Cable Winch

I think you’re not supposed to:
- Stand under something held by this cable
- Use it for motive power (?)
- Hang from it
I think they’re violating the first warning, as the cable holds the umbrella open over your head. On the other paw, it’s not a monster dead weight, so maybe it’s OK.

The food was pretty good.
2011-05-16