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

Bafang Brake Sensor Magnet Realignment

As mentioned earlier, the Bafang brake sensors on Mary’s Tour Easy require a magnet on the brake levers to activate the switches. They arrived with disk magnets that did not suit the levers, so I used neodymium “bar magnets”:

Tour Easy Bafang BBS02 – brake sensor – installed

That worked for a few rides, but the alignment turned out to be entirely too critical, because the magnetization is through the bar’s thin dimension, rather than along its length, making the field weakest in the direction of the switch.

Magnetic field visualization film shows the field null along the thin edge of the bar:

Neodymium bar magnet – edge field

That’s a slightly shorter magnet from a different toothbrush head, cemented edgewise into a holder conjured from the vasty digital deep:

Brake Magnet Mount – PrusaSlicer prevew

The field is much more uniform on the flat side of the bar:

Neodymium bar magnet – side field

Some double-sided foam tape snuggles the sensor and the magnet together on the brake lever:

Bafang Brake Sensor – released detail

I coated the magnet with JB Plastic Bonder urethane adhesive in the hope of filling any gaps in its nickel coating caused while extricating it from the toothbrush head.

The rusty screw head in the upper right positions the lever at the proper distance from the grip to suit Mary’s hand. An earlier version of the holder shows the alignment:

Bafang Brake Sensor – released position

The switch trips (opens) with the lever roughly parallel to the grip, again with the earlier holder:

Bafang Brake Sensor – activated position

A detailed view of the gap with the lever at the tripped position:

Bafang Brake Sensor – activated detail

The levers have enough travel to prevent accidental trips due to light finger pressure, which turned out to be a problem with the original end-on alignment.

The brake pads don’t quite touch the rim when the switch trips, so the motor has plenty of time to shut off before the brakes take effect. It also stops when the pedals stop turning, so we should not see any disagreement between motor and brakes as to the bike’s momentum.

The wider base on the new mounts makes them much more stable on the levers, although I don’t like having them stick up so far. Mounting everything underneath the levers would look better, but any problems will be more obvious with everything in plain sight.

I may affix the magnets directly to the levers with Plastic Bonder if the foam tape doesn’t live up to its reputation. Removing them would be more challenging; a shot with a small chisel should suffice.

2021-05-10
Vultures Sunning

Spotted after pre-season prep at Mary’s Vassar Farms garden:

Vultures sunning

It must feel really good up there atop the old barn, even if they’re sunning themselves to kill off parasites.

Taken with the Pixel 3a zoomed all the way in at 7× from a bit over 200 feet:

Vultures sunning – photo range

Then cropped and sharpened just a smidge. Not a great picture, but good enough for practical purposes; the Good Camera + Big Glass takes better pix and is too awkward to carry in my pocket.

2021-04-03
Discrete LM3909 Blue LED: Off at 1.0 V

The blue LED inside the radome got fainter as the alkaline AA cells faded away, but remained visible in a dark room until the discrete LM3909 circuitry stopped oscillating with the battery at 1.0 V. One of the cells had flatlined, with the other supplying what little current was needed.

The circuitry restarted with a pair of weak alkalines applying 2.4 V across the bus bars:

LM3909 Blue – 2.4 V alkaline

The LED waveform shows it needs about 2 V:

LM3909 Blue – 2.4 V alkaline

It’s barely visible in normal room light and strikingly bright at night.

2021-03-15
Adhesive vs. Concrete: Tenacity Thereof

Sometimes, sticky labels hold on forever:

Faded NO PARKiNG sign

It’s standing near what was once the Red Oaks Mill dam, which continues to disintegrate:

Red Oaks Mill Dam – 2021-02-25

Sixteen years ago, the dam was in better shape:

Red Oaks Mill Dam – 27 Feb 2005

Maybe the sign was shiny-new back then?

2021-03-07
Rust Never Sleeps

Spotted at the corner gas station on a recent walk:

Gas pump barrier – smashed

Judging from the tire tracks and extrapolating from recent weather, a snowplow driver misjudged the truck’s right-side clearance while backing.

That big steel tube didn’t put up nearly as much resistance as the architect figured after consulting the relevant building codes:

Gas pump barrier – right base

The paint seems to have been the only thing holding the other side together:

Gas pump barrier – left base

Google Streetview suggests the barriers were new-ish in May 2009:

Gas pump barrier – newish 2009-05

Steel is a great construction material, but it doesn’t fare well when installed at grade (or above) where it’s exposed to water and salt. On the other paw, they got over a decade out of it, so maybe it’s as good as it needs to be.

2021-02-14
123 Block Links: Blackened!

While looking for something else, I came across my bottle of Aluminum Black, so I just had to do this:

123 Block Links – blackened

Looks much snappier than the originals:

123 Block Links – trial assembly

Those are plain old alloy steel cap screws with a black oxide finish.

The Aluminum Black package directions tell you to apply it with a swab, rinse, and repeat, which seemed like a lot of work for a handful of pins. Instead, I poured a little into a pill bottle, dumped the pins in, and gave it a good shake to coat the pins, whereupon the cap blew off as the contents proceeded to boil merrily. A quick cold-water rinse calmed things down, with no particular harm done, although I had to chase the threads with a tap to get the black powder out. A layer of oil prettied them up nicely.

Today I Learned: the reaction between selenium dioxide and bare aluminum is strongly exothermic.

2021-02-11
Snow Flow

The recent snowfall arrived on a stiff north wind layering it atop the garage roof and sculpting the corner:

Snow – roof wave

The retaining wall along the driveway accumulated a thick coat that gradually peeled off as the weather warmed:

Snow – wall wave A

The wave crashed to the driveway in slow motion:

Snow – wall wave B

It seems to rebound from the wall, even though we know it’s been there all along:

Snow – wall wave C

This winter has more snow in store for us, but so far it’s been more decorative than disastrous.

One difference between deep snow and strong hurricanes: not much looting after the snow stops falling…

2021-02-07