Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
With the information you shared, we were able to successfully model and reconstruct the drive wheel in only a couple of days.
One useful thing we discovered is there’s a lot of room for error – so long as the pin catches and the wheel isn’t slipping on the motor shaft, the mechanism will work. The grooves and the interior radius of the original part aren’t critical.
Because of your heads up about Geneva wheels, I found this excellent website – https://newgottland.com/2012/01/08/make-geneva-wheels-of-any-size/ – which includes a link to a Geneva wheel calculator. With the measurements you sent and a measurement off of the pen carousel, the calculator generated near perfect dimensions for a replacement. There was a little sanding and rounding to fit but it was certainly within tolerance.
Interestingly, the pieces of the drive wheel that I pulled out of the case revealed a small hidden detail. On the underside, there’s a collar around the motor shaft that gives the cam an extra ~.03″ thickness. Presumably this is to help reduce friction during travel. Our prototype doesn’t take this detail into consideration – we’ve had no issues with friction, and we compensated for the thickness by making the pin a little longer – but it’s meaningful to note.
HP7475A Carousel Drive – cam1
The broken pieces also confirmed the thicknesses and radii of the original part, and so my partner was able to build an accurate technical drawing of the drive wheel for future fabrication.
While we intend to make a better replacement, our prototype was built with dense 1/8″ mat board, PVA glue, binder clips, and a short piece of wooden dowel from our bits box. Basically just stuff we had kicking around the studio. It’s held up shockingly well. A little dented around the edges from hitting the carousel, but there’s no slippage. I’m thinking I’ll use it until it falls apart, just to see how long it takes.
HP7475A Carousel Drive – repaired – cam2
Attached, find a technical drawing comparing the original drawing to our prototype (measured in good old fashioned 1980s inches); a photo of the retrieved piece, showing the collar on the reverse side; and a photo of the prototype in place. Feel free to share these – everyone deserves a working plotter!
7475a drive wheel
Once the carousel was working, my roommate – an electrical engineer – hooked me up with a custom serial cable, a Raspberry Pi, and a crash course in Python, so now that I can communicate with the plotter, the possibilities are staggering. I’m thrilled to add this machine to my print studio arsenal!
Over the course of those six years I’ve ridden about 6 × 2500 = 15000 miles, maybe more, maybe less. I can ride at 15 mph for a while, but 12 mph seems a more reasonable overall estimate, making for a bit over 1000 hours. Figure the bike spends that much time sitting outdoors at the far end of the ride and you’re looking at what 2000+ hours of sunlight does to ABS.
In addition to discoloration, the plates have become brittle, as shown in the chips in third one down, and permanently deformed due to the pressure of the nylon bolts compressing the black foam against the fairing.
A closer look at the top plate:
ABS Fairing Plates – 6 years – detail
My 3D print quality has improved a lot since then.
New plates of a different design are, as NASA puts it, “in work”.
The pix come from the new LiDE 120 scanner. It does a good job with the color, but has (for good reason) an essentially zero depth of field: if it’s not on the glass, it’s out of focus.
Came up from the Basement Laboratory to find my Dell Optiplex 980 PC had failed, with the power button and diagnostic 1 + 3 LEDs blinking amber. They built it back in June 2010, so section 3 of the Dell reference applies, the power supply status LED on the back panel was off, and, going straight to the heart of matter, I popped the top, disconnected the internal power supply cables, and poked the power supply test button:
Optiplex 980 Power Supply – rear panel test button
… and it’s dead.
Inside, the system board sports a Mini-ATX power supply connector:
Optiplex 980 – Mini-ATX power connector
I originally hoped to swap a supply from an Optiplex 755 (also in a Small Form Factor case) residing on the recycle heap, but it has an ordinary ATX connector:
Optiplex 755 – ATX power connector
So I moved the 980’s SSD and dual-Displayport video card into the 755, fired that devil up, and … it worked!
With my desktop back in action, albeit somewhat slower, I popped the dead supply’s case by violating the Warranty Void If This Label Removed sticker to unscrew the last screw:
The cluster of caps on the upper right have bulged pressure-relief lids, like this:
Optiplex 980 – Bulging capacitor 1
And this:
Optiplex 980 – Bulging capacitor 2
And this:
Optiplex 980 – Bulging capacitor 3
None had ruptured, but they’re obviously feeling a bit nauseous.
Given the 980’s mid-2010 manufacturing date, this probably isn’t capacitor plague, just simple overheating from operating in a dead-air zone amid all those heatsinks and wires. Some of the Usual Unnamed Sources suggest overheating the capacitors is how manufacturers ensure their hardware doesn’t last forever, without being obvious about planned obsolescence; I’m loathe to ascribe to malice what can be explained by design desperation.
A Genuine Dell replacement supply from eBay ($25 delivered) came from yet another “small form factor” Dell chassis, so it isn’t quite the same size, lacks a supply test button / LED status light, and doesn’t quite fit:
Optiplex 980 – replacement supply misfit
Nothing a sheet metal nibbling tool can’t fix, though, given I haven’t developed a deep emotional attachment to the chassis. I gnawed off the left side of the frame and squared up the rim around the lower screw, after which the opening fit the supply pretty well, although the latching tab bent up from the bottom of the chassis didn’t quite engage the far end of the supply. No big deal: it’s not in a high-vibration environment.
The new-to-me supply also carries an ATX connector, but the eBay seller included a Mini-ATX adapter. Jamming the adapter + wires into the space available required concerted muttering, assisted by tucking the SSD under the DVD-RW drive. No pictures, as it’s a classic seven pounds in a five pound box situation.
Our long-suffering kitchen scale lost a pair of feet, most likely becausethose two feet do most of the skidding as we slide it onto a shelf below a cabinet. The scale has (well, had) six silicone rubber feet:
Amazon EK3211 Scale – OEM foot
The vagaries of color photography turned a neutral-gray silicone disk into that weird blue.
A pair of ¼ inch disks punched from non-skid textured rubber tape fit perfectly into the recesses:
Amazon EK3211 Scale – tread foot
Now, we’ll see how tread adhesive withstands the same abuse.
Despite having sworn a mighty oath to the contrary, I found myself doing this again:
Clothes Rack – end clamp
A strut on the other end of the dowel split across its face:
Clothes Rack – split clamp
The white stuff is wood-filled epoxy, normally used to repair rotted wood, left over from another project. I’ll claim this tests its mechanical strength against peeling forces.
Easily determined by inspection: a sensible person would toss the rack, but …
The two knockoff Neopixeltestfixtures went dark while their USB charger accompanied me on a trip, so they spent a few days at ambient basement conditions. When I plugged them back into the charger, pretty much the entire array lit up in pinball panic mode:
WS2812 LED – test fixture multiple failures
Turns out three more WS2812 chips failed in quick succession. I’ve hotwired around the deaders (output disconnected, next chip input in parallel) and, as with the other zombies, they sometimes work and sometimes flicker. That’s five failures in 28 LEDs over four months, a bit under 3000 operating hours.
For lack of a better explanation: the cool chips pulled relatively moist air through their failed silicone encapsulation, quietly rotted out in the dark, then failed when reheated. After they spend enough time flailing around, the more-or-less normal operating temperatures drives out the moisture and they (sometimes) resume working.
Remember, all of them passed the Josh Sharpie Test, so you can’t identify weak ones ahead of time.
I wired a resistive joystick to the knockoff Nano controlling the crystal tester and connected the button to an analog input because I have a lot of those left over and why not. Unfortunately, the ADC returned a sequence of random-ish numbers indicating the button didn’t have a pullup to +5 V.
One might be forgiven for assuming the pads marked R5 would hold such a pullup resistor, had the joystick not been relentlessly cost-reduced:
Keyes resistive joystick – R5 location
One would, of course, be completely wrong.
Having been around this blockseveral times, I measured the pad-to-pin resistances and found R5 firmly affixed to the GND and +5V pins, with the SW (a.k.a. button) pin floating free. Pressing the joystick hat closes the switch next to R5, thereby connecting the SW pin to GND.
Baffles me. Maybe a fresh intern did the PCB layout and just misplaced the resistor?
So I soldered an ordinary resistor (*) between the +5 V and SW pins:
Keyes resistive joystick – button pullup
Now it works just as it should.
(*) For long-lost reasons, I have a zillion 12.4 kΩ 1% resistors appearing in place of simple 10 kΩ resistors.
The Smell of Molten Projects in the Morning 