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

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

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.
2016-06-20
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

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…

2016-05-26
Blender Bearing Repair: Round Three

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.

2016-05-18
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

Spiders seem no less bizarre in white light:

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 …

2016-05-13
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

Good news comes to those who wait:

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.

2016-04-29
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

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

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.

2016-04-26
Belt Pack Zipper Pull Re-Repair

In our last episode, the zipper tab on my belt pack had worn through:

Eroded YKK Zipper Tab

I “fixed” that by the simple expedient of running a key ring through the latch that used to hold the tab. That held for half a year, which isn’t to be sniffed at for a zero-cost repair.

A few days ago, the abused latch popped off the slider, leaving the NSA tag and ring in my hand:

Belt Pack Zipper – missing tab and latch

I scuffed up the surface with a file to provide a bit more grip for the inevitable epoxy, then clamped a brass tube athwart the slider:

Belt Pack Zipper – wired brass tube

The tube ID passes the ring with enough clearance to make it work out. The general idea is that the tube provides rigidity for the ring, the wires hold the tube against the pull, and the epoxy holds the wires in place. I fully expect the sharp edges around the tube’s ID will gradually wear away.

Threading 14 mil stainless steel wire through the slider’s pivot hole:

Belt Pack Zipper – wire opened end

… and under the latch guide:

Belt Pack Zipper – wire closed end

… required a few tries and produced some nasty puncture wounds, but eventually it all hung together long enough to let me tuck some JB Kwik epoxy into all the nooks and crannies:

Belt Pack Zipper – epoxy curing

That’s wide masking tape covering the work area. As it turned out, good preparation like that meant I didn’t slobber epoxy anywhere it shouldn’t go; had I omitted the tape, there’d be a smear down the side of the pack.

Fast-forward to the next morning and it’s all good:

Belt Pack Zipper – repaired

The missing latch locked the slider in place, but I think I can eke out a miserable existence with a loose slider…

2016-04-21