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
At first glance, I thought Mary had taken a tour of The Great Swamp south of the Vassar Farm gardens:
APRS Bicycle Tracking – Flying High
Having helped put the fence up, I’m absolutely certain nothing growing in the garden could get her to 4373 feet, much less boost the bike that high.
Before that, it seems she did some high-speed tunneling:
2015-05-10 18:17:31 EDT: KF4NGN-9>T1TP4X,WIDE1-1,WIDE2-1,qAR,KB2ZE-4:`eP}nAIb/"/k}
type: location
format: mice
srccallsign: KF4NGN-9
dstcallsign: T1TP4X
latitude: 41.67466666666667 °
longitude: -73.88283333333334 °
course: 345 °
speed: 42.596 km/h
altitude: -371 m
symboltable: /
symbolcode: b
mbits: 101
posresolution: 18.52 m
posambiguity: 0
The bike’s altitude began falling while she was on the way to the garden, from a reasonable 66 meters on the entrance road, bottoming out at -371 m as she hit 42.6 km/h (!), rising to 1341 meters with the bike leaning against a fence post, and returning to 53 meters as she started riding home.
Obviously, you shouldn’t trust consumer-grade GPS tracks without verification: it can get perfectly bogus numbers from fixes with poor satellite geometry. Altitude values tend to be only close, at best, even when you’re not too fussy about accuracy.
Combining all the records so far into one giant lump:
Well Pit Air Temperature – 2014-10 to 2015-04
Yes, the air temperature really did hover around freezing for two weeks in mid-February. If it didn’t require hoisting a four-inch concrete slab with a rusted lift ring, I’d affix a logger to the copper water pipe running across the pit for some direct samples of the actual water temperature.
It hasn’t ever frozen in the last half-century or so; I’m not going to start worrying now…
The HP 7475A plotter comes with a transparent smoke-brown plastic flip-up lid covering the carousel and pen holder, presumably to keep dust and fingers out of the moving parts. That lid also has has the side effect of limiting the pen length, presumably because HP didn’t want the 7475A to eat into their large-format plotter market. In any event, removing the lid leaves another barrier to longer pens: the rugged plastic case between the carousel and the pen holder.
That’s from an earlier test, before I sawed the slot in the case, with all the machinery behind the pen holder in full view.
The test plot, with the proper pen colors and widths loaded in the carousel, looks pretty good:
HP7475A – Sakura Micro Pens – self-test plot
The pen holder wasn’t intended to support a long pen, so that shaft tends to torque the pen tip out of position, particularly while drawing characters:
HP 7475A – long black pen – misalignment
The various pen tips don’t all point to the same place:
HP 7475A – long RGBK pen misalignment
That could be non-concentric pen adapters, misalignment in the pen holder, or slightly off-center pen nibs. The offsets between the colors remains consistent in all the bar-chart columns, so the pen adapters aren’t shifting in the holder.
The worst-case error between bar-chart rectangles amounts to 0.5 mm parallel to the pen holder motion and 0.8 mm parallel to the paper motion. In round numbers, the pen tip is 30 mm from the flange, so moving it 0.5 mm to the side tips the pen 1°. The flange is 17 mm OD, which means a 1° tilt raises one edge by 0.3 mm or both edges by ±0.15 mm. Given a 0.25 mm 3D printed thread thickness, that’s certainly within reach of a random plastic blob.
Looking closely at the printed-and-glued flange shows plenty of room for misunderstanding betwixt pen and holder, even after cleaning off all that PETG hair:
HP7475A – Sakura Micro Pen Adapter – vs HP pen
Given that the Sakura pens aren’t intended for this application, a slight tip misalignment due to body molding tolerances isn’t unreasonable; a perfect adapter might not solve the problem.
The HP maintenance manual lists a BASIC program to produce a test plot that verifies pen alignment, although the prospect of transliterating 2+ pages of quoted strings from a scanned document doesn’t fill me with desire.
Having run off four quick prints with identical settings, I measured the thickness of the skirt threads around each object:
Skirt Thread Consistency
They’re all slightly thicker than the nominal 0.25 mm layer thickness, but centered within ±0.02 mm of the average 0.27 mm. Tweaking the G92 offset in the startup G-Code by 0.02 would fix that.
The 0.29 mm skirt surrounded the first object, which had a truly cold start: 14 °C ambient in the Basement Laboratory. After that, they’re pretty much identical.
Some informal measurements over a few days suggests the actual repeatability might be ±0.05 mm, which is Good Enough for layers around 0.20 to 0.25 mm.
The larger skirt suggests that the platform has a slight tilt, but the caliper resolution is only 0.01 mm.
When I realigned everything after installing the V4 hot end, the last set of thinwall boxes looked like this:
The blue trace shows the groundwater temperature at the inlet pipe. The minimum values should be pretty close to the actual ground temperature about four feet down, which seems roughly constant at 37 °F for March.
The red trace comes from the datalogger dangling in the well pit in the back yard, directly under one of the vent holes, so it’s recording the air temperature in a below-grade chamber.
The green trace shows the attic air temperature, which is strongly influenced by sun on the (white) asphalt shingle roof. That said, the air temperature gets a lot lower than any of the below-grade loggers; it’s fair to say they’re recording something fairly close to the actual ground temperature.
The turkey flock that normally lives along the Wappingers Creek valley, downslope from the back yard, has emerged for the ritual spring foraging:
Turkey flock – 0
And posturing:
Turkey flock – 1
And just moseying around:
Turkey flock – 2
You can match the trees and identify some duplicated birds, but the flock seems stable around a dozen. They used to deploy skirmish lines upwards of two dozen bird and we’ve recently counted 19; we think foxes have been encouraging better control of wandering chicks.
You’ll note the complete lack of understory vegetation; the only remaining plants can withstand continuous deer browsing. Deer have clipped all of the evergreens five feet off the ground, even through they don’t normally eat evergreens…
In fact, there’s no new tree growth in the Hudson Valley, because tree seedlings don’t stand a chance.
The Smell of Molten Projects in the Morning 