Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The never-sufficiently-to-be-damned O-rings in the kitchen’s American Standard faucet wore out again; the faucet spout went from a tolerable piddle to a major flow over the course of a few weeks.
The inner circumference of the bottom O-ring had most of the wear:
American Standard faucet – worn lower o-ring
In cross-section, it’s more of a D-ring:
American Standard faucet – worn lower o-ring – section
Once again, I soaked the spout & pillar in vinegar to remove the mineral deposits (despite the soft water), gave them a light sanding with 800 grit paper to regularize the surfaces, cleaned everything up, lubed it with petroleum jelly, and it’s all good.
Disassembly and replacement went smoothly, mostly because I could look up what I did before and avoid all the usual mistakes.
Our standard dishwasher loadout changed a while back, so I ran off more protectors to fill the bottom rack. The crystalline look of natural PETG is probably wasted in there, even though it puts the old, rather yellowed, PLA protectors to shame:
Dishwasher Rack Protectors – old PLA new PETG
Dollops of silicone sealant hold them in place: the bigger the blob, the better the job.
We don’t activate the drying heater, so the plastic doesn’t get exposed to absurdly high temperatures. As nearly as I can tell, those PLA protectors remain in fine physical condition, even though they’re turning an odd color.
The support structures peeled out easily with a fingernail pull:
Dishwasher Rack Protectors – 0.20 mm PETG bridging – detail
PETG doesn’t bridge well, as shown by the gaps between the support ridges. Those 0.20 mm layers seemed skimpy for lightly supported PETG, so I ran another set at 0.25 mm:
Dishwasher Rack Protectors – 0.25 mm PETG bridging – detail
Not quite enough improvement for a Happy Dance, although fine for the application.
We look forward to seeing what grows in those little crevices…
I bought a 2 inch Micro-Mark Mini Miter / Cut-off Saw to cut screws & brass tubing, in the hopes that it would be somewhat better than the essentially equivalent Harbor Freight offering. I think that’s true, but it’s a near thing.
Apparently, the saws all come from the same factory with the same bass-ackwards vise:
Micro-Mark Cutoff Saw – vise side view
The V-groove should be on the fixed jaw, where it would more-or-less precisely align rods / cylinders with the blade. The moveable jaw isn’t dovetailed to the base of the vise, so it ends up wherever it stops and, somehow, they managed to machine the end of the screw shaft off-center from the shaft, so the moveable jaw moves in a small circle as you tighten it.
A small punch mark locks the jaw to the screw; you can pull the disk on the shaft past the indentation by turning the knob with sufficient enthusiasm:
Micro-Mark Cutoff Saw – clamp jaw detail
The hole in the vise, just under the disk, lets somebody whack the jaw with a punch.
Some machining or an entirely new vise setup lies in the future of this thing.
I mounted it on a scrap of countertop by transfer-punching the base holes, only to discover that the punch didn’t leave a mark for one hole, even though a dent was clearly visible at the bottom of the hole with the saw on the countertop.
A bit of headscratching later:
Micro-Mark Cutoff Saw – unfinished casting hole
Apparently the core for that hole in the injection mold didn’t seat quite right. The layer was thin enough to drill out easily.
The mower tried to eat a protruding root, emitted a horrible crash, and ran poorly until I shut it off, after which it refused to restart. Hoping against hope that the flywheel’s aluminum key had sheared, I pulled the cover, removed the starter, and found:
Mower flywheel key
Alas, the key is in fine shape. I made the two diagonal scratches to confirm it really is aluminum.
After letting the mower sit for a day, it started and ran briefly, blatted a giant backfire that probably startled the neighborhood (because I had the exhaust aimed into the garage, which served as a wonderful resonator), died a sudden death, then made clanking sounds whenever I pulled the rope. Something is definitely broken inside, but I suspect diagnosing & fixing it will require more time and money than is justified.
I no longer form deep emotional attachments to lawn mowers, so I ordered a similar one online and the local Sears had it ready for pickup in an hour.
If I had to pull the flywheel, I’d tap the two obvious holes (one behind the shaft in the picture) and gimmick up a puller with two matching screws around a central bolt that does the heavy lifting; I can’t justify the Special Service Tool I’m sure it requires.
The old mower lasted an hour at the foot of the driveway with a “FREE – Engine probably severely broken” sign affixed to its handle; both parties got a great deal on that transaction!
With a new motor and controller in the reconfigured SqWr Power Wheels chassis, I made a few measurements under somewhat less than controlled conditions, with the butt end of the chassis on jack stands. The general idea was to find out what the “lightly loaded” condition looked like in terms of motor current; after some mechanical and electrical improvements, we’ll be in a better position to determine the battery load & suchlike.
Preliminary measurements:
Motor DC resistance: 0.7 Ω (meter lead resistance 0.2 Ω, so don’t trust it)
Motor winding inductance: 128 µH
Motor shaft key: 1/8 inch (keyway chewed by pulley setscrews, needs matching shaft flats)
Twist-grip throttle applies nonzero voltage when released: possibly damaged
With everything in position and the Tek 6303 probe set for 10 A/div, this is what happens when you push the deadman switch:
Out V I 10 A – start transient
Obviously, the motor controller takes much too long to wake up & sense the current.
The initial slope of that current waveform looks like 80 A/360 µs = 220 kA/s. The upper trace gives the motor voltage, so 23 V / (220 kA/s) = 104 µH, surprisingly close to the measured 128 µH.
Deploying the mighty Tek CT-5 (with an enclosed A6302), cranking the gain to 50 A/div, and poking the deadman again:
Out V I 50 A – start transient full
During that initial pulse, the controller connects the battery directly to the motor, so you’re looking directly at 200 A of battery current. For reasons that aren’t relevant here, the mandatory 60 A safety fuse isn’t present, although it should be able to withstand a millisecond or two of moderate overload without blowing.
With that out of the way and the motor running at a few hundred RPM, due to the nonzero twist-grip output voltage with no throttle applied, the controller actually does PWM pretty much as you’d expect:
Out V I 10 A – run low speed
It’s not clear what caused the small dent just before the middle pulse; perhaps the motor commutator switched from one winding to the next.
The battery current will be much lower than the motor current in this mode, roughly (motor current) * (PWM fraction). We haven’t verified that, but for 30% PWM it should be around 5 A = 15 A * 0.30. The actual battery current looks smoother than I expected, although I have no traces to show for it; more study is needed.
Eks once again graciously loaned me his Tek current probes; this whole Power Wheels mess motivated me to get off my ass and accumulate my own collection, about which more later.
According to the Forester’s manual, the Tire Pressure Monitoring System kicks in after the car reaches 25 mph. It evidently takes a while to figure things out after that, because the TPMS light blinked on a mile from home on the way to Mary’s Vassar Farms garden. I pulled into the next parking lot, measured 20 psi in the left rear tire, then found this staring me in the eye:
Forester – left rear tire with screw
Well, that certainly simplified the diagnosis!
I unloaded two bags of shredded leaves and a pile of hoses, swapped in the (limited use, donut-style) spare tire, and continued the mission.
The TPMS light wasn’t on when I drove to Squidwrench the previous evening. Judging from the wear, that screw appeared during the various errands following our 800 mile road trip, which is good news of a sort, and depressurized the tire over the course of a day or two.
The receipt from the fix-it folks cautions that a plug is a temporary fix, because “the injury has compromised the integrity of the tire”. On the other paw, the Forester manual tells me “All four tires must be the same in terms of manufacturer, brand (tread pattern), construction, and size. You are advised to replace the tires with new ones that are identical to those fitted as standard equipment” and then provides a checklist:
When you replacing or installing tire(s), all four tires must be the same for following items.
(a) Size
(b) Circumference
(c) Speed symbol
(d) Load index
(e) Construction
(f) Manufacturer
(g) Brand (tread pattern)
(h) Degrees of wear
There’s absolutely no way to get an identical replacement tire, let alone one with the same tread wear, but I am so unready to replace all four tires after 12 k miles / 2 years.
After half a dozen years, the bearings in the blender impeller felt pretty bad:
Defunct blender bearings
I wiped everything clean, found the box containing the box containing the tube of bearings, packed the base with more silicone grease, reassembled everything in reverse order, and it’s all good again.
The first repair lasted for a year and the second for six, so I think overpacking the base with grease helped a lot. Maybe I’m getting better at ignoring horrible grinding sounds.
I can do this twice more, although the Jesus clip holding the shaft into the bearing stack definitely needs replacing.
The Smell of Molten Projects in the Morning 