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Archive for category Software

Xiaomi-Dafang Hacks: FTP Server for Camera Files

Since the PiHole runs all the time, it now hosts an FTP server to stash snapshots from the cameras onto a 64 GB USB stick. I installed ProFTPD, which Just Worked with a few configuration tweaks:

UseIPv6             off
ServerName          "PiHole"
DefaultRoot         /mnt/cameras
RequireValidShell   off

The cameras use the BusyBox ftpput command to stash their images (with the hostname prepended), which requires a few changes to motion.conf in the cameras:

ftp_snapshot=true
ftp_host="192.168.1.2"
ftp_port=21
ftp_username=$(/bin/hostname)
ftp_password="make up your own"
ftp_stills_dir=$(/bin/hostname)

The last line uses a separate directory for each camera, although they quickly ran into the FAT32 limit of 64 K files per directory; reformatting the USB stick with an ext3 filesystem solved that problem.

Fortunately, nothing much ever happens around here

New Utility Pole Arrives
New Utility Pole Arrives
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Beware the Domain Squatters

A squatter has taken over a defunct domain at the far end of a link buried somewhere in the 3800 posts you find here. In place of the useful page I saw, you’ll see this stylin’ popover:

Domain Squat - engineeration dot com
Domain Squat – engineeration dot com

The “standard security check” is a nice touch, although you should keep in mind the Dilbert cartoon about unexpected side effects.

The actual URL, which I will not make clickable, includes the domain ffgetsplendidapps, which tells you just about everything you need to know about what’s going on.

Because they’re squatting, “continue directly to your destination” means being dumped into a Google search after they’ve meddled with your browser & system configuration. Clicking the inconspicuous × in the upper right closes the popover and dumps you into the search, perhaps before doing anything.

I have no good (i.e., automated) way to find broken links and, as far as I know, there is no way to automatically detect domain squatting, so you’re on your own.

Trust, but verify!

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Step2 Garden Seat: Replacement Seat

A pair of Step2 rolling garden seats (they have a new version) served in Mary’s gardens long enough to give their seat panels precarious cracks:

Step2 Seat - OEM seat
Step2 Seat – OEM seat

The underside was giving way, too:

Step2 Seat - cracks
Step2 Seat – cracks

We agreed the new seat could be much simpler, although it must still hinge upward, so I conjured a pair of hinges from the vasty digital deep:

Rolling Cart Hinges - solid model - bottom
Rolling Cart Hinges – solid model – bottom

The woodpile disgorged a slab of 1/4 inch = 6 mm plywood (used in a defunct project) of just about the right size and we agreed a few holes wouldn’t be a problem for its projected ahem use case:

Step2 Seat - assembled
Step2 Seat – assembled

The screw holes on the hinge tops will let me run machine screws all the way through, should that be necessary. So far, a quartet of self-tapping sheet metal (!) screws are holding firm.

Rolling Cart Hinges - solid model - top
Rolling Cart Hinges – solid model – top

A closer look at the hinges in real life:

Step2 Seat - top view
Step2 Seat – top view

The solid model now caps the holes; I can drill them out should the need arise.

From the bottom:

Step2 Seat - bottom view
Step2 Seat – bottom view

Three coats of white exterior paint make it blindingly bright in the sun, although we expect a week or two in the garden will knock the shine right off:

Step2 Seat - painted
Step2 Seat – painted

After the first coat, I conjured a drying rack from a bamboo skewer, a cardboard flap, and some hot-melt glue:

Step2 Seat - drying fixture
Step2 Seat – drying fixture

Three small scars on the seat bottom were deemed acceptable.

The OpenSCAD source code as a GitHub Gist:

This original doodle gives the key dimensions, apart from the rounded rear edge required so the seat can pivot vertically upward:

Cart Hinge - dimension doodle
Cart Hinge – dimension doodle

The second seat looks just like this one, so life is good …

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MPCNC: Calculating Spring Rates

Calculate the spring rates for the drag knife, diamond engraver, and collet pen holders by measuring the downforce every 0.5 mm (or so):

LM12UU Collet Pen Holder - spring rate test
LM12UU Collet Pen Holder – spring rate test

Then plotting the data points and eyeballing a straight-line curve fit:

MPCNC - Drag Knife Holder - spring constant
MPCNC – Drag Knife Holder – spring constant

Doing it on hard mode definitely has a certain old-school charm. The graph highlights mis-measured data and similar problems, because, if you don’t see a pretty nearly straight line, something’s gone awry.

But we live in the future, so there’s an easier way:

Droid48 - Spring Rate - Linear Fit coefficients
Droid48 – Spring Rate – Linear Fit coefficients

Well, OK, it’s the future as of the early 1990s, when HP introduced its HP 48 calculators. I’m using the Droid48 emulator on my ancient Google Pixel: living in the past, right here in the future.

Start by firing up the STAT library (cyan arrow, then the 5 key), selecting Fit Data … from the dropdown list, then selecting the Linear Fit model:

Droid48 - Spring Rate - Linear Fit screen
Droid48 – Spring Rate – Linear Fit screen

Then tap EDIT and enter the data in a tiny spreadsheet:

Droid48 - Spring Rate - Linear Fit data
Droid48 – Spring Rate – Linear Fit data

My default “engineering mode” numeric display format doesn’t show well on the tiny screen. Tapping the WID→ key helps a bit, but shorter numbers would be better.

With the data entered, set an X value and tap the PRED key to get the corresponding Y value:

Droid48 - Spring Rate - Linear Fit prediction
Droid48 – Spring Rate – Linear Fit prediction

Tapping the OK button puts the line’s coefficients on the stack, as shown in the first picture. Write ’em on a strip of tape, stick to the top of the holder, and it’s all good:

LM12UU Collet Pen Holder - test plot - overview
LM12UU Collet Pen Holder – test plot – overview

Works for me, anyhow.

HP still has the HP 48g manuals online. The (unofficial) HP Museum has a page on the HP 48S. More than you want to know about the 48 series.

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MPCNC Collet Pen Holder: LM12UU Edition

Encouraged by the smooth running of the LM12UU drag knife mount, I chopped off another length of 12 mm shaft:

LM12UU Collet Pen Holder - sawing shaft
LM12UU Collet Pen Holder – sawing shaft

The MicroMark Cut-off saw was barely up to the task; I must do something about its craptastic “vise”. In any event, the wet rags kept the shaft plenty cool and the ShopVac hose directly behind the motor sucked away all of the flying grit.

The reason I used an abrasive wheel: the shaft is case-hardened and the outer millimeter or two is hard enough to repel a carbide cutter:

LM12UU Collet Pen Holder - drilling shaft
LM12UU Collet Pen Holder – drilling shaft

Fortunately, the middle remains soft enough to drill a hole for the collet pen holder, which I turned down to a uniform 8 mm (-ish) diameter:

LM12UU Collet Pen Holder - turning collet body
LM12UU Collet Pen Holder – turning collet body

Slather JB Kwik epoxy along the threads, insert into the shaft, wipe off the excess, and looks almost like a Real Product:

LM12UU Collet Pen Holder - finished body
LM12UU Collet Pen Holder – finished body

The far end of the shaft recesses the collet a few millimeters to retain the spring around the pen body, which will also require a knurled ring around the outside so you (well, I) can tighten the collet around the pen tip.

Start the ring by center-drilling an absurdly long aluminum rod in the steady rest:

M12UU Collet Pen Holder - center drilling
M12UU Collet Pen Holder – center drilling

Although it’s not obvious, I cleaned up the OD before applying the knurling tool:

LM12UU Collet Pen Holder - knurling
LM12UU Collet Pen Holder – knurling

For some unknown reason, it seemed like a Good Idea to knurl without the steady rest, perhaps to avoid deepening the ring where the jaws slide, but Tiny Lathe™ definitely wasn’t up to the challenge. The knurling wheels aren’t quite concentric on their bores and their shafts have plenty of play, so I got to watch the big live center and tailstock wobbulate as the rod turned.

With the steady rest back in place, drill out the rod to match the shaft’s 12 mm OD:

LM12UU Collet Pen Holder - drilling shaft
LM12UU Collet Pen Holder – drilling shaft

All my “metric” drilling uses hard-inch drills approximating the metric dimensions, of course, because USA.

Clean up the ring face, file a chamfer on the edge, and part it off:

LM12UU Collet Pen Holder - parting ring
LM12UU Collet Pen Holder – parting ring

Turn some PVC pipe to a suitable length, slit one side so it can collapse to match the ring OD, wrap shimstock to protect those lovely knurls, and face off all the ugly:

LM12UU Collet Pen Holder - knurled ring facing
LM12UU Collet Pen Holder – knurled ring facing

Tweak the drag knife’s solid model for a different spring from the collection and up the hole OD in the plate to clear the largest pen cartridge in the current collection:

Collet Holder - LM12UU - solid model
Collet Holder – LM12UU – solid model

Convince all the parts to fly in formation, then measure the spring rate:

LM12UU Collet Pen Holder - spring rate test
LM12UU Collet Pen Holder – spring rate test

Which works out to be 128 g + 54 g/mm:

LM12UU Collet Pen Holder - test plot - overview
LM12UU Collet Pen Holder – test plot – overview

I forgot the knurled ring must clear the screws and, ideally, the nyloc nuts. Which it does, after I carefully aligned each nut with a flat exactly tangent to the ring. Whew!

A closer look at the business end:

LM12UU Collet Pen Holder - test plot - detail
LM12UU Collet Pen Holder – test plot – detail

The shaft has 5 mm of travel, far more than enough for the MPCNC’s platform. Plotting at -1 mm applies 180 g of downforce; the test pattern shown above varies the depth from 0.0 mm in steps of -0.1 mm; anything beyond -0.2 mm gets plenty of ink.

Now I have a pen holder, a diamond scribe, and a drag knife with (almost) exactly the same “tool offset” from the alignment camera, thereby eliminating an opportunity to screw up.

The OpenSCAD source code as a GitHub Gist:

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Runtime Error!

Spotted high on the wall of the local USPS office:

Windows Runtime Error - VLC - monitor
Windows Runtime Error – VLC – monitor

A closer look:

Windows Runtime Error - VLC
Windows Runtime Error – VLC

Huh.

The USPS uses VLC. Who knew?

I darken their doorway so infrequently I have no idea what’s normally displayed up there. Surely it shows advertisements for USPS products, which begs the question: why VLC?

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Wrapping GCMC Text Around Arcs

GCMC includes a typeset function converting a more-or-less ASCII string into the coordinate points (a “vectorlist” containing a “path”) defining its character strokes and pen motions. The coordinates are relative to an origin at the lower-left corner of the line, with the font’s capital-X height set to 1.0, so you apply a scale function to make them whatever size you want and hand them to the engrave library routine, which squirts the corresponding G-Code into the output file.

Such G-Code can annotate plots:

Guilloche 213478839
Guilloche 213478839

Given that the plots appear on relentlessly circular CDs and hard drive platters, It Would Be Nice to wrap text around a circular arc, thusly:

Diamond Scribe - LM3UU - arc text - first light
Diamond Scribe – LM3UU – arc text – first light

The scaled coordinates cover a distance L along a straight line, so putting them on an arc will cover the same distance. The arc is part of a circle with radius R and a circumference 2πR, so … polar coordinates to the rescue!

The total text length L corresponds to the total angle A along the arc:

A = 360° L / 2πR

It’s entirely possible to have a text line longer than the entire circumference of the circle, whereupon the right end overlaps the left. Smaller characters fit better on smaller circles:

Arc Lettering - Small radius test - NCViewer
Arc Lettering – Small radius test – NCViewer

The X coordinate of each point in the path (always positive from the X origin) in the path gives its angle (positive counterclockwise) from 0°:

a = 360° x / 2πR (say "eks")

You can add a constant angle of either sign to slew the whole text arc around the center point.

The letter baseline Y=0 sits at radius R, so the Y coordinate of each point (positive above and negative below the Y=0 baseline) gives its radius r:

r = R - y

That puts the bottom of the text outward, so it reads properly when you’re facing the center point.

Homework: Tweak the signs so it reads properly when you’re standing inside the circle reading outward.

Converting from polar back to XY:

x = r × cos(a) (say "times")
y = r × sin(a)

You can add an XY offset to the result, thereby plunking the point wherever you want.

This obviously works best for small characters relative to the arc radius, as the lines connecting the points remain resolutely straight. That’s probably what you wanted anyway, but letters like, say, “m” definitely manspread.

Overall, it looks pretty good:

Arc Lettering - test plot overview - NCViewer
Arc Lettering – test plot overview – NCViewer

A doodle helped lay out the geometry:

Arc Lettering - geometry doodles
Arc Lettering – geometry doodles

The GCMC source code as a GitHub Gist:

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