Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
We’ve been using Cateye Astrale “computers” on our bikes for decades, mostly to get the cadence function. After all this time, we pretty much know how fast to pedal, but old habits die hard.
The cadence sensor counts pedal revolutions per minute, which requires a magnet on the crank arm. They provide a small plastic-encased magnet with a sticky-tape strip that’s worked fine on our previous crank arms.
Our daughter’s Tour Easy arrived with fancy curved pedal crank arms that put the cadence sensor magnet much too far from the frame. You really want the magnet & sensor close to the bottom bracket so that it doesn’t get kicked and doesn’t snag anything as you pedal, but that just wasn’t going to work out here.
A turd of JB Weld epoxy putty solved the problem: mix up a generous blob, shape it into a pedestal, glom the magnet atop it, adjust so the magnet is parallel to and properly spaced from the sensor, then smooth the contours a bit.
Add the cable tie for extra security; you don’t want to lose the magnet by the side of the road!
The black electrical tape is mildly ugly, but serves the purpose of keeping the cable from flapping in the breeze. The adhesive lasts about a year, then it’s time for routine maintenance anyway.
My buddy Eks asked me to help fix his new-to-him and guaranteed broken Tek 492 spectrum analyzer, which turned into a tour-de-force effort. One sub-project involved sucking the bits out of an existing “known-good” Tek memory card, which meant building a backplane connector and a circuit that behaved like a 6800 microcontroller… fortunately, it could be a lot slower.
[Update: It seems searches involving “Tektronix 492” produce this page. You may also be interested in these posts…
The HEX files you’ll need to replace failed ROMs and EPROMs
If those aren’t what you’re looking for, note that the correct spelling is “Tektronix“.
Good luck fixing that gadget: it’s a great instrument when it works!]
You can tell just by looking that this board was designed back in the day when PCB layout involved flexible adhesive tape traces and little sticky donut pads. Ground plane? We don’t need no stinkin’ ground plane!
Actually, it’s a four-layer board done with the usual Tek attention to detail. They didn’t need a ground plane because they knew what they were doing. Remember, this is in a spectrum analyzer with an 18-GHz bandwidth and 80 dB dynamic range; a little digital hum and buzz just wouldn’t go unnoticed.
Tek 492 Backplane Geometry
Anyhow, the backplane pins are on a 0.150-inch grid within each block. The center block (pins 13-36) is 0.200 inches from the left block (pins 1-12) and 0.250 from the right block (pins 37-60).
That means the left and right blocks are neatly aligned on the same 0.150-inch grid, with the middle block offset by 50 mils. You can’t plug the board in backwards unless you really work at it.
Of course, Eks had some genuine gold-plated Tek pins in his stash: 24 mils square and 32 mils across the diagonal. They have 1/4″ clear above the crimped area that anchors them to the black plastic spacer and are 1/2″ tall overall. They’re not standard header pins, but I suspect you could use some newfangled pins in a pinch.
Here’s what the reader board finally looked like, hacked traces and all, with the board connector to the rear. The memory board didn’t use all the backplane pins, so I only populated the ones that did something useful. The power-and-ground pins (left side of right pin block) stand separately from the other because I had to solder them to both the top and the bottom of the board: no plated-through holes!
Tek 492 Memory Board Reader
I cannot imagine this being useful to anybody else, but I defined an Eagle part for the connector so I could CNC-drill the board. Drop me a note and I’ll send it to you.
Although recumbent bikes use ordinary bicycle components, they tend to have somewhat different frame geometries (to put it mildly). Our Tour Easy ‘bents seem to put a particular strain on the front derailleur cables, perhaps because the cable enters from a different angle than the derailleur designers expected. The little finger that’s supposed to guide the cable actually concentrates all the bending force at one spot… precisely where the cable breaks.
If you look carefully, you’ll see a little brass disk (between the derailleur body and cable) that cradles the cable. I made that for the previous derailleur, but this one has Yet Another Geometry. I know there’s a difference between “high pull” and “low pull” front derailleurs, and perhaps this is the wrong one for this application, but there seems no algorithmic way to sort this stuff out.
Cable guide pulley
The solution is to make Yet Another Cable Guide Pulley, with a groove around the perimeter, an off-center hole, and a notch to clear the finger. It’s not exactly a pulley, but I’m not sure what else to call it. Maybe just a cable guide?
This was a quick-and-dirty manual lathe project, two days before leaving on a trip: turn down some brass stock, put a groove around the perimeter, part it off, drill a hole, and cut the notch. Not a trace of CNC to be found: all done by guess and by gosh, marked out with Sharpies on the actual part in real time running.
The general notion is that the cable rides the groove smoothly throughout the derailleur’s entire travel range and, thus, doesn’t bend around the finger. This changes the shift geometry just slightly, but, fortunately, long-wheelbase ‘bents have a sufficiently relaxed chainline that indexed front shifting isn’t much of a problem even with slightly misplaced positions. Besides, that’s why SRAM grip-shifter have all those clicky stops, right?
(The shifting is actually a bit goobered, with the outer chainring shift a bit too close to the middle. When we get back, I’ll re-do this with somewhat more attention to detail.)
Pulley in action
Here’s what it looks like in action. I’ve had good success with this sort of thing over the years, so I think this one will work just fine, too. It simply takes one broken cable on each new derailleur to spin up enough enthusiasm for making Yet Another Pulley…
Being cyclists, we were doing the resuable-water-bottle thing long before it became trendy, but now that we use hydration packs, we just tote bottles along when we’re driving or on some other sort of outing. Eventually the bottles wear out / get lost and we page a new one in from the essentially infinite stash in the bottle cupboard.
This one had a cap that simply couldn’t be pried open with bare hands, no how, no way. I eventually got it open by main force and the threat of high temperatures.
Turns out there were two problems: the aperture in the pull-up ring is a wee bit small on the sealing nub and the ridge on the screw cap is about two wee bits large for the recess in the ring.
The former succumbed to an O (letter Oh) drill, which I pulled & pushed through the hole by hand to enlarge the aperture from 0.320 to 0.332. It still seals reasonably well, although it’ll pee a thin stream under more pressure than you should apply to such a bottle, which means I put a slight scratch on the aperture.
The latter required gently shaving the ridge with a box cutter (gasp). It’s still rather stiff, but entirely workable. That doesn’t affect the seal, because the ring’s skirt is a snug fit against the screw cap.
Why not just throw the fool thing out? After all, it’s just a freebie water bottle…
We run on the “Use it up, wear it out, fix it once, wear it out again, then put it on the shelf because maybe you can use the parts for something” principle.
Now, that’s not the way things are done these days, but it works for us…
The front ball joint on the mirror on Mary’s helmet loosened enough that the mirror blew out of position every time we got up to a decent traveling speed. I’ve repaired these mirrors several times before; they’re plastic and tend to fracture / wear out / break at inconvenient moments.
The first pic shows the mirror (the black surface is reflecting the dark floor joists overhead) with an old blob of epoxy that repaired a break in the outer socket. The socket originally had stylin’ curves joining it to the mirror, which proved to be weak spots that required epoxy fortification.
This time the socket split axially on the side away from the mirror, which released the pressure on the ball socket that seats into it. I found a chunk of brass tube that fit snugly over the socket, then carved some clearance for the existing epoxy blob. The key feature is that the tube remains a ring, rather than a C-shaped sheet. to maintain pressure around the socket.
Clamping the reinforcement ring
Here are the various bits, with the reinforcing ring clamped in place. I coated the socket exterior with JB Weld epoxy, slipped the ring in place, and tapped it down with a brass hammer to seat flush with the front face of the socket. That left gaps between the socket opening and the tube that I eased more epoxy into with an awl. A bit more epoxy around the exterior smoothed over that ragged edge.
The strut at the bottom of the picture ends in a ball joint held by a socket that slips into the mirror socket. The loose brass ring above the mirror is some shim stock that I added some years ago to take up slop between the ball socket and the mirror socket and tighten the ball joint. I suppose that pressure eventually split the outer socket, but so it goes.
Repaired mirror joint
The clamp squished the outer socket enough to snug it around the ball socket, so when I reassembled the mirror it was fine. To be sure, I dunked the ball in my lifetime supply of Brownell’s Powdered Rosin for a bit more non-slip stickiness.
I have a box full of defunct bike helmet mirrors, dating back to those old wire-frame square mirrors that clamped onto the original Bell helmets. The newer plastic ones just don’t last; we ride our bikes a lot and even fancy engineering plastic isn’t nearly durable enough. A few bits of metal here and there would dramatically improve the results!
I’m going to build some durable wire-frame mirrors, but … this will keep us on the road for a while. I suppose I should make a preemptive repair on my helmet mirror while I’m thinking of it…
Here’s a quick-and-easy way to improve the odds of your arriving home safely after dark: add snippets of retroreflective tape to the inside of the rims on your bike.
Do half the rim in one color and leave the other half untaped (or taped in a contrasting color) so that the rim flashes as the wheel rotates. I originally applied orange tape, of which I have very nearly a lifetime supply, then added white when I got a sheet as part of a surplus deal.
At 15 mph the 20-inch front wheel blinks at about 4 Hz, which is wonderfully attention-getting. The rear wheel, a more common 700C size, blinks at 3 Hz.
It helps to measure the space between spokes, then set up a template to cut all the tape pieces the same length. Wipe the big chunks of dirt off the rim, then remove the remaining grunge with alcohol so the tape actually sticks.
New York State vehicle law considers reflectorized tires as equal to those in-the-spokes reflectors, which is a Good Thing.
The more you look like a UFO after dark, the less surprised the drivers are and the less hassle you get.
A small improvement: add a snippet of heat stink shrink tubing to the screw in the L-shaped hold-down clamps and the screw won’t go walkabout in your tooling widget case.
Make it the same length as the distance from the clamp to the surface and it’ll remind you how far to screw on the T-nut when you swap the clamps from tooling plate to milling machine table.
Sherline clamp screws with heatshrink
Sherline clamp in action
The Sherline Mill Vise (PN 3551) comes with a set of clamps. They’re also available separately as the 4-Jaw Hold-Down Set (PN 3058).
The Smell of Molten Projects in the Morning 