Archive for June, 2009

Bees!

Swarm cluster

Swarm cluster

We hived a giant swarm!

They’re doing well in their new home, building out comb on the foundation. The queen is in good shape, laying eggs as soon as the workers finish the cells. The workers seem to be feeding pollen directly to the larvae rather than storing it, which makes perfect sense. They’re taking two quarts of 1:1 sugar water every day!

Either you already know what this is all about or you really don’t want to know.

‘Nuff said…

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Fixing a Too-small Derailleur Cable Ferrule

Brass tubing to enlarge ferrule

Brass tubing to enlarge ferrule

While replacing the rear derailleur on Mary’s Tour Easy, I rediscovered that I have two different cable sizes in my stash: large brake cables and small derailleur cables.

The large ferrules are 0.235 inches in diameter, the smaller 0.187 inches. The brazed-on cable-stop sockets are obviously sized for the larger ferrules, which makes perfect sense.

If you put a small ferrule in a large stop, it tends to cant whichever way the cable pulls it. That results in the cable sawing into the edge of the ferrule… and that results in excess friction and sometimes a broken cable.

In the past I’ve snipped out little brass shimstock rectangles, wrapped them around mandrels, and generally spent a lot of time fiddling around. This time I remembered to rummage in my collection of brass tubing cutoffs, which yielded a pair of very-nearly-perfect slip fit pieces that neatly adapted the small ferrules to the large stops.

Rear shift cable with modified ferrules

Rear shift cable with modified ferrules

Life is good…

I have no idea what the cables look like on weight-weenie exotic-frame bikes. For sure, this isn’t a trick for hydraulic disk brakes.

Incidentally, the cable housing length worked out to 130 mm. Neither of the charts in the SRAM X.7 instructions matched the TE’s butt end; the seat stay angle is halfway between what’s normal for diamond-frame bikes. So we picked a reasonable length and it seems to be OK.

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Ending the Firefox “needs to be restarted” Loop

Scenario: You install the latest Firefox update, restart as requested, and then get stuck in a loop where the popup window at the top of the browser keeps telling you to restart.

That bug (270303 “your browser has been updated and needs to be restarted”) and its ilk have been repeatedly fixed, on every version since about 3.0.2, and (it seems) to no avail.

What worked for me after updating to Firefox 3.0.11 was to close the browser and then:

touch ~/.mozilla/firefox/your-own-uuid-here.default/localstore.rdf

That’s on Ubuntu 9.04, of course…

Update: Same problem with the 3.0.12 update. Same hack-job fix. Makes you go hmmm.

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Plug Alignment for ICOM IC-Z1A Radio

Plugs and jack alignment plates

Plugs and jack alignment plates

As I mentioned there, I originally connected my bicycle-mobile amateur radio gadget to the ICOM IC-Z1A radio using separate mic and speaker plugs. That seemed like a good idea, but bicycles vibrate a lot and the plugs apply enough leverage to the jacks inside the radio to pry them right off the PCB. That requires a protracted repair session that I never wanted to do again.

The solution is to mount both plugs rigidly on the radio so that they simply can’t move. I dithered for a while and finally decided that function trumps good looks on this project, particularly given that our radios spend their entire lives inside a bag behind the bike seats.

The top picture shows the small aluminum plates I made to align the plugs to the HT jacks, along with a plastic gluing fixture to hold the plugs parallel while the epoxy cures. If you just jam the plugs into the radio without an alignment fixture, you will glue the plugs together in such a way that they cannot be removed: the radio does not hold the shafts exactly parallel!

Plug stabilization - What Not To Do

Plug stabilization - What Not To Do

How do I know? Well, I tried doing exactly that by simply epoxying the existing plugs into place, applying enough epoxy putty to stabilize the plugs against the radio. Looks reasonable, but when it came time to take them out (and you will want to take them out, trust me) they are firmly and permanently embedded. I had to carve them apart to get them out.

The mic, speaker, and coaxial power jacks are 10 mm on center. The 2.5 mm mic plug has a small shoulder that required a matching recess in the plate, while the 3.5 mm speaker plug is basically a cylinder. I don’t use the coaxial power jack, having hacked an alkaline battery pack with Anderson Powerpoles. The plate’s external contour matches the flat area atop the radio around the jacks.

You could lay out and drill close-enough holes by hand, use a step drill to make the shoulder recess, and then let the epoxy do the final alignment. However, you want the center-to-center distance exactly spot-on correct, as the plugs won’t mate properly otherwise. I turned it into a CNC project for my Sherline mill, of course, but that’s just because I have one.

HT Plugs in gluing fixture

HT Plugs in gluing fixture

This picture shows two plugs epoxied into the plate. While the epoxy cures, the plate rests atop the fixture with the two plugs vertical and their shell flanges flush against it. I applied the epoxy with a toothpick and worked it into the gap between the threads and the plate.

The end result will be a pair of plugs that exactly match the radio’s jacks in a plate that sits firmly atop the radio’s case. You should find that the plugs snap firmly into place and the entire assembly is absolutely rigid.

Caveat: don’t use an aluminum plate if your radio depends on separate electrical connections for the mic and speaker plug shells. The IC-Z1A has isolated shells, but remains happy when they’re connected. My Kenwood TH-F6A HT uses the shells for entirely different functions and will not work with them shorted together.

With the epoxy cured, wire the connections as usual. I had a small cable with enough tiny wires to put the mic conductors in their own shielded pair, but that’s likely overkill.

Finished plugs with epoxy blob

Finished plugs with epoxy blob

You could machine a nice enclosure, but I simply molded an epoxy putty turd around the connections, shells, and cable. The trick is to wait until it’s nearly cured, plug it into the radio, then shave off whatever gets in the way of the knobs, antenna plug, and other appurtenances.

It may not look elegant, but it works great!

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Bicycle Mobile Mic Amp Debug: It’s the Connector

The radio on Mary’s bike has been misbehaving over the last few months: the PTT button on the handlebars occasionally had no effect. Debugging this sort of intermittent problem is quite difficult, as it would sometimes fail and repair itself before we could get stopped in a safe place where I could poke around in the wiring.

After months of this nonsense, I narrowed the failure down to the short cable from the HT’s mic jack to the interface board: by positioning the cable just so, the radio would work fine for days or weeks at a time. I taped the thing in position and all was well, at least for a few days or weeks at a time.

HT audio interface - 2001

HT audio interface - 2001

HT audio interface - 2009

HT audio interface - 2009

These two pictures show what the interface looked like back in 2001 when I put it together (modified from another version I did in 1997!) and what it looks like today. The most significant change is in the plugs connecting the whole affair to the HT: a CNC-machined plate holds them perfectly parallel at the proper spacing and an epoxy-putty turd fuses them into a rigid mass. More on that sub-project tomorrow…

Loose plugs, it turns out, vibrate the HT’s jacks right off the circuit board in short order and those jacks are a major pain to replace. Ask me how I know…

The wire break seemed to be precisely where the mic cable exits the epoxy turd. You’d expect a fatigue fracture to occur at that spot, so I wasn’t particularly surprised, although I was amazed that the thing hadn’t failed completely over the months I spend fiddling with it. I finally resolved to fix this once and for all, which meant either flaying the cable and patching the wire in situ or rebuilding the whole connector assembly. Either choice requires enough fiddly work to discourage even me.

Sooo, disconnect everything & haul it to the Basement Laboratory, Electronics Workbench Division…

Before cutting into the cable, I measured the mic voltage on the PCB and tried to make the thing fail on the bench. The HT (an ancient ICOM IC-Z1A) normally presents 3.5 V DC on the mic wire and the external PTT switch pulls it to ground through a 22 kΩ (or 33 kΩ or thereabouts) resistor. The mic audio is a small AC signal riding a volt or so of DC bias with the PTT active.

The wire measured maybe 0.25 volts and the PTT dragged it flat dead to ground. Yup, through that honkin’ big resistor. Well, maybe the last conductor in that mic wire had finally broken, right there on the bench?

Measured from the 2.5 mm plug tip conductor (tip = mic, ring = 3.5 V DC, sleeve = mic common) to the PCB pad on the PC, the mic wire stubbornly read 0.0 Ω, regardless of any wiggling & jiggling I applied to the cable. But no voltage got through from the radio to the board…

Sticking a bare 2.5 mm plug into the HT mic jack produced a steady 3.5 V on the tip lug. Reinstalling my epoxy-turd plug assembly produced either 0.25 or 3.5 V, depending on whether I twisted the thing this way or that way.

Ah-ha! Gotcha!

Pulled out my lifetime supply of Caig DeoxIT Red, applied a minute drop to the end of the mic plug, rammed it home & yanked it out several times, wiped off the residue, and the PTT now works perfectly. Did the same thing to the adjacent speaker plug, just on general principles, and I suspect that’ll be all good, too.

Diagnosis: oxidation or accumulated crud on the mic jack inside the radio.

Now, to try it out on the bike and see how long this fix lasts. Anything will work fine on the bench, but very few things survive for long on a bicycle.

Memo to Self: It’s always the connectors. Unless it’s the wires.

Here’s the schematic, just in case you’re wondering. I wouldn’t do it this way today, but that’s because I’ve learned a bit over the last decade or so…

[Update: A more recent attempt is there.]

IC-Z1A Mic Amp Schematic

IC-Z1A Mic Amp Schematic

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Security by Photographic Obscurity: FAIL

Gas Storage Tank

Gas Storage Tank

We biked along the Poughkeepsie waterfront and spotted this stately gas storage tank. The shape tells you it’s a pressure vessel, not a simple fluid tank. I think Central Hudson has an underwater gas pipeline across the Hudson right about there; the waterfront is rife with oil storage tanks and suchlike, although less than in days of yore.

As you might expect, I took the picture from a public area, pretty much in front of a house across the street. It’s not like this was a risky high-security red-flag penetration operation; we rode to the end of Dutchess Avenue (the better part of 600 feet), soaked up some of the decaying industrial-age vibe, turned around, and rode back up the hill.

Dutchess Avenue - Google Obscured View

Dutchess Avenue - Google Obscured View

I made a ten-cent bet with myself that the Google-Eye view of the area would be blurred out “for security reasons” and, yup, won that sucker. This isn’t a case of JPG compression: notice how (relatively) crisp the railroad tracks are?

Dutchess Ave - Topo Map

Dutchess Ave - Topo Map

The 1955 topographic map hanging on our wall (I’m a map junkie) was revised in 1981 and leaves very little to the imagination. It not only shows oil storage tanks standing on those now-empty concrete pads, but it also labels the area. Admittedly, it doesn’t show the gas tank, so the tank hasn’t been there for more than, oh, a quarter-century.

I submit to you that the best way for an evildoer to pick a high-value target is to browse the maps and look for low-res areas. Here in mid-state New York, that’s an infallible way to find things like big petroleum storage facilities (or just look along the waterfront), airports with military-grade runways (the Dutchess County Airport evidently doesn’t count), oil / coal / nuke power plants, and good stuff like that. Then the bad guy gets in his car, drives over, gets some ground truth, and away they go.

A lazy bad guy could even write a Google Maps app that quietly and slowly scanned a given area for low-res points of interest.

That’s what Bruce Schneier calls a Movie Plot Threat. Ruining the resolution doesn’t change anything; you don’t need high-res imagery to blow something up.

Sheesh & similar remarks.

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SRAM Twist Grip Shifter Pointer Repair

The little red pointer inside my Tour Easy’s rear SRAM Grip-Shift broke. Back in the old days, this wouldn’t be a problem, as we used friction shifters on the downtube (as we rode to school, uphill, in the snow, both ways) and knew by feel which gear was engaged. But that was then, this is now, and fixing things is what I do anyway.

The pointer turned out to be a thin plastic strip, molded into an L with a domed arch over the pointy end. It simply rests in a slot in the shifter mechanism, held in place by the transparent cover (which, mercifully, came off without dismantling the bike or even removing the cable).

I made a similar replacement from thin red-anodized aluminum, but that didn’t work out at all. The mechanism snaps from one gear to the next at roughly the speed of heat, accelerating the pointer so rapidly that the aluminum deformed. Score one for plastic!

Actually, I made two aluminum pointers. Prototype One vanished into the Sargasso heap in front of the Solvents & Lubricants Shelves at the first upshift; that’s when I discovered just how much snap that shifter applies to the pointer. Made another one, installed the cover, and then discovered it wasn’t going to work.

So I applied some Plastruct solvent adhesive to the broken plastic bits, lined the parts up on my crusty surface plate, applied a bit of gentle pressure overnight, and in the morning had a like-new pointer. It installed just fine and works like the original.

Solvent-bonded plastic is supposed to be just about as strong as the original material. We’ll see just how long this repair lasts…

Pop Quiz: Do you know the first four derivatives of position w.r.t. time?

Answer: Velocity, acceleration, jerk, and snap. You could look it up…

Update: Alas, the repair lasted only about two weeks before failing at the same spot. Some deep rummaging produced a similar (but more thoroughly dead) SRAM shifter. Turns out the pointers are similar, so I salvaged the older one. Ya gotta have stuff… and remember it, too, which is becoming something of a challenge.

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