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.

Tag: Repairs

If it used to work, it can work again

  • Craftsman Mower Flywheel Key: Intact

    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
    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!

  • Squidwrench Power Wheels Racer: Motor Current

    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
    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
    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
    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.

  • Forester: TPMS FTW, Sorta-Kinda

    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
    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.

    We shall see how this works out…

  • Blender Bearing Repair: Round Three

    After half a dozen years, the bearings in the blender impeller felt pretty bad:

    Defunct blender bearings
    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.

  • Hard Drive Platter Mood Light: Failed LED Debugging Assistance

    Another of the knockoff Neopixels in the Hard Drive Platter Mood Light failed, even limited to PWM 63 to reduce the temperature. This time, however, I had some help finding the failed blue LED:

    Hard Drive Mood Light - failed LED with spider - green
    Hard Drive Mood Light – failed LED with spider – green

    Spiders seem no less bizarre in white light:

    Hard Drive Mood Light - failed LED with spider - white
    Hard Drive Mood Light – failed LED with spider – white

    A day later, she’d built a small web, presumably to improve the odds of catching something yummy. Who am I to disagree?

    I should set up a test fixture for all the knockoff Neopixels and run some numbers. They’re definitely a disappointment, even to a bottom feeder such as I …

  • Road Conditions: 2816 Rt 376 Northbound Sinkhole Patched

    By my count, four NYSDOT repair crews, one sent specifically to repair this sinkhole, managed to not patch it during the last nine months:

    Rt 376 2016-04-20 - Northbound milepost 1110 - sinkhole
    Rt 376 2016-04-20 – Northbound milepost 1110 – sinkhole

    Good news comes to those who wait:

    Rt 376 2016-04-21 - Northbound milepost 1110 - sinkhole
    Rt 376 2016-04-21 – Northbound milepost 1110 – sinkhole

    It didn’t involve waiting: by random chance, a fifth NYSDOT road repair crew happened to be in that area when Mary rode by. She stopped directly atop the sinkhole and screamed at the flagger until he came over. She explained the problem and, wonder of wonders, this time they put asphalt in the right spot.

    The patch looks hand-tamped and will pop out after a while, but it’ll be great while it lasts.

     

  • OttLite LED Conversion: Lamp Shell Auto-Disassembly

    The converted OttLite hit the floor again and, this time, the shell around the lamp popped free. Given that I didn’t know how to take it apart before, this is new news.

    There’s a small snap latch inside the bottom / inner surface:

    OttLite LED Conversion - lamp shell - ventral
    OttLite LED Conversion – lamp shell – ventral

    And two guide notches + latch nubs inside the top / outer surface:

    OttLite LED Conversion - lamp shell - dorsal
    OttLite LED Conversion – lamp shell – dorsal

    So, if you had to get it apart by hand, a spudger-like tool applied to the bottom / inside of the shell and a bit of tugging should do the trick.

    It snapped back together without incident, but I really must figure out a bigger base for the damn thing.