Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
I’ve managed to lose enough weight off my butt (it doesn’t go away, it just becomes leg muscle for a few months) that I must move the seat on my Tour Easy forward maybe 5 mm. Alas, I’ve run out of adjustment room: the frame is a Medium Large and I probably should have gotten a Medium; that decision was forced by getting a much-too-small Linear many years ago.
The general idea here is to bolt the seat to an aluminum circumferential clamp just forward of the plate and tubes that normally secure the seat to the frame. That moves the clamping bolts about 15 cm forward, but they slide in slots along the seat bottom.
The bolts are 1/4-20 stainless carriage bolts, with the square shank under the head sliding in those slots. I think the clamp can be about the same thickness as the existing tubes, so the same bolts will work.
The main frame tube runs slightly above the two small tubes that stiffen the rear triangle. It’s not clear those clearances in the clamp must be contoured to fit the tubes exactly; a simple flat cutout will probably work just fine.
The top of the clamp must have two bosses to support the seat base around the clamping screws. A line of rivets down the middle secures the seat base to the contoured (carbon?) fiberglass pan holding the foam cushion.
We’re getting set up for a bicycle vacation and I did a quick tire inspection… good thing, too, considering the gashes I found in the rear tire on Mary’s Tour Easy.
I put Schwalbe Marathon 700x35C tires on the back of our ‘bents, for well and good reason: Marathons have plenty of rubber and include a Kevlar puncture-resistant layer. In this case, that was just barely enough!
Here’s a cross-section through the tire; the Kevlar layer is yellow, with the tire carcass fibers inward of that.
Schwalbe Marathon tire cross-section
The greenish-yellow tint in the left-hand gash (in the top picture) is the Slime tire liner (they prefer “tube protector”) showing through. Here’s what the liner looked like after we pulled the tire off; the liner shows some damage, but it’s just surface scuffing.
Scuffs on tire liner
Quite by coincidence, the gashes straddled the overlapped end of the liner. The end of the liner is on the tube side; I haven’t trimmed or tapered the end of this one.
Here’s what the inside of the tire looked like; the Kevlar fought the gashes to a standstill and left the carcass mostly intact. The painted and illustrated fingernails belong to my shop assistant.
Scuffs inside tire carcass
Here’s a cross-section through the Kevlar layer. I don’t know what Mary ran over, but it was most likely a sizable chunk of the broken glass that litters the roads around here. I doubt anybody gets prosecuted for littering, but as far as I’m concerned, a fitting punishment would be collecting the glass from a few miles of roadway: crawling on hands and knees, picking up fragments with their lips.
Cuts through tire anti-puncture layer
I put a new tube in a new Marathon (for obvious reasons, I have a supply of both on the shelf at all times), we positioned the liner, pumped it up, and it’s all good.
With the jack in hand, I idly poked a coaxial plug into it and realized that the amount the plug stuck out was just about exactly equal to the thickness of the black plastic cap on its tip. Some rummaging turned up one of the six plugs with a missing tip, at which point both the problem and its solution were obvious.
Broken vs original coaxial power tips
A bit of tedious work with a tiny screwdriver and a needle convinced the socket to disgorge the plastic ring from its bowels …
Broken tip extracted from jack
Now, I suppose I could have figured this out without taking the case apart, but actually fixing the problem would still require surgery, soooo there’s no wasted effort. That’s my story and I’m sticking with it.
If you think you could extract that ring from the outside, there’s a joke about that.
I put the case back together with a few dabs of silicone snot adhesive (despite what I know about letting acetic acid loose near electronics) to anchor the circuit board, applied a belly band of tastefully color-coordinated (i.e. silver) duct tape, and it’s all good.
Actually, the pack was stone cold dead until I plugged it into the charger to reset its battery protection circuitry. Evidently, disconnecting and reconnecting the battery tripped the protection logic. I’ve seen that in other Li-Ion packs, so it wasn’t quite so scary as it was the first time around.
As for the coaxial power tip: a dab of solvent glue, an overnight clamping session, and I think it’ll work fine forever more.
I should machine up some stabilizing collars around the sockets to match that obvious shoulder on the plug, shouldn’t I?
The power lead into the Li-Ion pack I’m using for the bike radio became badly intermittent on a recent ride. When I got back I swapped in a different pack and the problem Went Away, but I noticed that the coaxial power plug didn’t seem to seat all the way into the jack on the failed pack. I’d noticed that before, although I attributed it to getting two different sets of the packs; it didn’t seem to make any difference.
Given that I was going to have to either repair or replace the jack, dismantling the offending pack was next on the list. Some preliminary poking showed that there were no screws concealed under the label, so the two halves of the pack were either snapped or bonded together.
The case didn’t respond to the usual wedging and prying by revealing an opening, which suggested that it was bonded. That meant I must saw the thing apart.
I set up a 31-mil slitting saw on the Sherline and clamped the pack atop a random plastic slab atop the tooling plate. The Sherline’s limited throat depth meant I had to cut the far side of the pack. I aligned the saw to the Z-axis level of the joint along the middle of the pack by eyeballometric guesstimation.
Slitting saw setup
Key point:
You absolutely do not want to saw into a lithium-ion cell, not even a little bit.
Therefore:
The pack must be aligned parallel to the cutter’s travel
The cuts must proceed in tiny increments, and
You must verify that each cut doesn’t reveal any surprises.
In this setup, the pack aligns against a clamp on the left side and to a parallel block (removed while cutting) along the rear edge of the tooling plate. I could then unclamp the pack, rotate it to put the next edge in place, and use the same XYZ origin with the edge parallel to X.
Here’s the view from the back of the table.
Sawing the case
I ran the spindle at 5 k RPM and cut about 15 inch/secminute. I’m sure the pros do it faster, but that was enough to warm up the blade and that’s fast enough for me. [Update: typo on the units. Thanks!]
Cuts were 0.020 inch per pass, which is about 0.5 mm. I expected the case to be some hard-metric dimension and wasn’t disappointed.
After the cuts reached 0.060 inch, I manage to pry the remaining plastic in the joint apart and split the halves apart along the connectors and LEDs at the front where I couldn’t do any sawing.
Here’s a close look at the cut, just above the battery terminals. The case turned out to be 2 mm thick, about 0.080 inch, so I was just about all the way through. The cut was perfectly aligned with the case and cracked open neatly along the entire length.
Tight tolerance on the cut depth
An interior view, showing that the cells adhered to the left half of the case and the electronics to the right: of course. I pried the cells loose from the left side, which provided enough access to unsolder the things, as the terminals were against the case. Notice that there’s absolutely nothing between the inside of the case and the outside of the cell, so cutting just slightly too deep would be a Bad Thing™.
First look inside the case
After a bit of work, here’s the entire layout…
Battery pack internal layout
Much to my surprise, the battery consists of two series-connected sets of three cells: 2 x 3.7 V = 7.4 V. I expected three series sets for about 3 x 3.7 = 11.1 V, with a linear regulator down to the 9.0 V output.
As it turns out, they used two switching regulators: the one between the two triplets controls the charging voltage and the one to the lower-left boosts the battery to the pack’s 9.0 V output. I had hoped for a resistor divider that I could tweak to get 9.6 V out, but it certainly wasn’t obvious.
I unsoldered the cells, dismounted the circuit board, and puzzled over it for a bit, after which the problem was obvious.
The story continues tomorrow, with a dramatic denouement…
The PTT switch for the amateur radio on my bike got erratic: pushing the button didn’t seem to be producing reliable RF. I’d have sworn when I bought the switches that they were washable-during-PCB-assembly: at least moderately sealed.
Wrong.
Turns out there’s only the seal you get from snug-fitting mechanical parts. I carved off the square aluminum bezel and found an ordinary dome switch underneath, with contacts that actually looked better than you’d expect after half a decade on a bike. But, yes, I could see why it was erratic.
Lacking anything smarter, I installed another one, just like the other one, with a square of Kapton tape over the button. Not a great seal, but maybe it’ll be Good Enough.
Here’s what the button looked like in happier times…
My Sony DSC-H5 eats NiMH cells like candy, which means I must haul along a pocketful of the things. That means I often wind up with a case containing one charged pair and one uncharged pair.
Ditto for swapping cells in the blinky lights on our bikes.
Pop quiz: which pair is which?
Battery Charge State Reminder
It’s pretty easy:
Nose-to-tail = as in the camera = charge ’em
Nose-to-nose = as in the charger = ready to use
You could do some remote psychoanalysis based on that sort of behavior, but you’d be completely right.
Went on a ride around the block and after about 4 miles discovered I had no rear brakes. Well, the brakes were there and doing the right mechanical things, but without much friction.
Did an expedient repair by squeezing strips of paper between the pads and the rim, then rolling the wheel. Came out black and graphite-looking, not oily, but didn’t improve the braking.
Rolled the bike into the shop after the ride; 23 miles without a rear brake gets my immediate attention. Wiped a lot of black graphite-looking schmutz off the rim using denatured alcohol, filed the well-glazed pads to a nice finish, and reinstalled.
These are Aztek pad inserts, which I’m trying out to see how they work. So far, not much; they seem less grippy than the ordinary Aztek pads (on the front and previously on the back) and certainly much more prone to glazing.
The Smell of Molten Projects in the Morning 