Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
This Philips LumiLED app note gives some specs on automotive lighting. The one we bikies all tend to ignore is the surface area: greater than 37.5 square centimeters for rear combination stop-turn fixtures. Call it a scant 4 inches in diameter. You’ve never seen a bike light that large, have you?
LED combo tail stop light
Maybe the right thing to do is start with a street-legal truck light and build some electronics around it. This is a 4 inch diameter, 44 LED rear light with both taillight and brake light terminals. At 12 V, the taillight draws 10 mA and the brake light is 250 mA. Got it from Gemplers with a recent order, but they’re certainly not the optimum supplier if that’s all you’re buying.
Obviously, it’s unreasonable to run a 3 watt taillight on a bike, as the most recent crop of single-LED killer headlights are merely a watt or three. Battery life remains a problem.
At 10% duty cycle the brake LEDs would average 300 mW. That might be roughly comparable to the running lights on some cars these days.
With the taillight constantly energized and the brake flashing at 4 Hz, it’d be 120 + 0.5 * 300 = 270 mW.
That’s more reasonable. With a 50% efficient upconverter to 12 V, that’s half a watt. Start with 4 AA cells, triple the voltage, draw 100 mA, runtime is 1500 / 100 = 15 hours. Good enough.
And it ought to be attention-getting enough for anybody! The only trouble will be fitting the damn thing on the back of the bike; fortunately, ‘bents have plenty of room behind the seat, so maybe attaching it below the top seat rail will work.
Memo to Self: The rear reflector must be something like 3 inches in diameter, too. We ignore that spec, too.
Let’s quote that text so you can read it (or click the picture for a bigger one):
Yeah… we’re talking down there. With lots of supporting data that says prolonged riding while your boys are numb is a no-no, we decided to build a saddle you can fine-tune to fit… you.
Speaking of prolonged riding, the current hour records:
Upright bike: 30.882 miles
Recumbent: 56.2948 miles
Sam Whittingham (who also holds that recumbent hour record) recently set the new human-powered land speed record at Battle Mountain: 82.43 miles per hour. Yup, pedaling a bicycle, on level ground, in minimal wind.
Admittedly, he was riding a recumbent that bears as much relation to the Tour Easy I ride as a Formula One car bears to yours. On the other paw, those Tour de France bikes aren’t exactly factory stock, either.
If you want to go as fast as you can on a bike, you want a recumbent. Unless, of course, you’re doing UCI races, in which case you may go as fast as they’ll allow you and wreck your body in the process.
When you get back from a ride on a recumbent bike, no matter how long you rode the bike, not only do all your parts still work, but nothing hurts. What’s not to like?
My earlier musing on bike performance is there. Clicking on the “Recumbent Bicycling” category summons forth more posts…
I need an LED taillight (and maybe headlight) with a metal case and far more LEDs than seems reasonable. This is a doodle to sort out some ideas… not all of which will work out properly.
The general notion is that one can put today’s crop of ultrasuperbright 5 mm LEDs to good use. While the Luxeon & Cree multi-watt LEDs are good for lighting up the roadway, they’re really too bright and power-hungry for rear-facing lights. Mostly, you want bright lights facing aft, but the beam pattern & optical niceness really aren’t too critical as long as you’re not wasting too many photons by lighting up the bushes.
I think, anyway. Must build one and see how it works. I know that a narrow beam is not a Good Thing, as cars do not approach from directly behind and it make aiming the light rather too finicky.
The problem with commercial bike taillights is that they use piddly little LEDs and not enough of them. If you’ve ever actually overtaken a bicyclist at night with a blinky LED taillight, you’ve seen the problem: they’re too damn small. Automobile taillights must have a very large surface area for well and good reason.
So the diagram in the pic explores the notion of arranging a bunch of red & amber LEDs in a fairly compact array. The shaded ones are red, the open ones are amber (with two more side-facing ambers to meet legal requirements), and there are eight of each. The OD is about 40 mm. Figure 5 mm LEDs with 2.5 mm of aluminum shell between them. If the center four LEDs were spaced right, an axial (socket-head cap?) screw could hold the entire affair together.
Turns out both the red & amber LEDs in the bags of 100 I just got from Hong Kong run at 2 V forward drop @ 30-ish mA, so that’s 16 V total for eight in series.
Four AA NiMH cells fit neatly behind the array, so the supply will be 4 – 5 V, more or less. The outer casing could be plastic pipe.
What to do for a battery charging port? Must be mostly weatherproof. Ugh.
Rather than a regulated supply and a current sink / resistor, use an inductor: build up the desired forward current by shorting the inductor to ground, then snap the juice into the LEDs. The voltage ratio is about 4:1, so the discharge will happen 4x faster than the charge for a duty cycle around 20%. At that ratio, you can kick maybe 50 mA into the poor things.
Governing equation: V = L (ΔI/ΔT)
If they’re running continuously, 2 V x 50 mA x 0.2 = 20 mW. The full array of red or amber is 160 mW, 320 mW for both. If you’re powering them at 10% duty cycle, then the average power dissipation is pretty low. Not much need for an external heatsink in any event.
A 1 kHz overall cycle means a 200 µs inductor charging period. With low batteries at 4 V and 50 mA peak current, the inductor is 16 mH. That’s a lot of inductor. I have a Coilcraft SMD design kit that goes up to 1 mH: 12 µs charge and 16 kHz overall. Well, I wouldn’t be able to hear that.
No need for current sensing if the microcontroller can monitor battery voltage and adjust the charge duration to suit; three or four durations would suffice. Needs an ADC input or an analog window comparator.
Automotive LED taillights seem to run at about 10% duty cycle just above my flicker fusion frequency; say between 50 – 100 Hz. If that’s true, red & amber could be “on” simultaneously, but actually occupy different time slots within a 100 Hz repeat and keep the overall duty cycle very low.
I’d like red on continuously (10% of every 10 ms) with amber blinking at 4 Hz with a 50% duty cycle. When they’re both on the total would be 60% duty.
The legal status of blinking taillights is ambiguous, as is their color; more there. Motorcycles may have headlight modulators. Bikes, not so much.
Battery life: assume crappy 1500 mAh cells to 1 V/cell. Red = 50 mA x 0.2 x 0.1 = 1 mA. Amber = 50 mA x 0.2 x 0.5 = 5 mA. Thus 1500 / 6 = 250 hours. Figure half of that due to crappy efficiency, it’s still a week or two of riding.
Rather than a power switch, use a vibration sensor: if the bike’s parked, shut off the light after maybe 5 minutes. It wouldn’t go off when you’re on the bike, even stopped at a light, because you’re always wobbling around a little.
Memo to Self: put the side LEDs on the case split line?
Every now and then I notice the pedals are getting further away on my Tour Easy recumbent, which means it’s time to snug up the seat lace again. The lace cord has a Kevlar core, so it’s not very stretchy, but over the course of a few thousand miles either it stretches or the seat mesh relaxes.
Here’s the only tool I’ve found that works for this purpose:
Stanley 82-113 Hook Tool: "The Hemorrhoid Picker"
That’s what a friend calls his, anyway.
It’s from Stanley and not in their current website listing, but they do offer the 78-393 – 4 Piece Hook and Pick Set, which looks to have a tool sporting the same hook end with a different (and much smaller) handle. IIRC, I got this one several-many years ago at Wal-Mart; maybe it’s a special-issue part number just for their shelves?
What you do is work your way from the bottom of the seat lacing on one side all the way to the top, pulling out the slack as you go. At the top of that side, pull the accumulated cord into the knot, then start at the bottom of the other side. When you’ve got both sides pulled taut, knot up the slack again and you’re done.
Needless to say, you can give yourself a King Hell puncture wound with that thing…
Vibration is a real killer for bike-mounted hardware. The antenna mast on my bike has been unscrewing itself, despite my repeated attempts to tighten it. Fortunately, I’ve managed to notice the rattle before the mast falls off into traffic.
We’ll see if a dab of medium strength (blue) Loctite will do the job.
One thing to worry about: this is an electrical as well as a mechanical joint. I hope there’s still enough metal-to-metal contact to get RF energy to the radiating part of the whip!
[Update: Yup, works just like you’d expect. Problem solved.]
The antennas on the other two bikes have remained tight, so maybe it’s just that my riding style generates more vibration? Hard to imagine; it’s not like I venture off-road.
More details on the homebrew mount are there and how commercial mounts fail are there.
The unsightly masking tape wrap is where I attached a reflector for a (rare) after-dark ride a while ago. Making a set of bushings for the reflector clamps is a low-priority job in the queue right now.
As mentioned there, I have a pair of ERRC’s Easy Reacher underseat packs. They’re supported by an Easy Reacher rack that’s specifically designed for Tour Easy bikes.
Perhaps because I carry dense stuff in the packs, they tend to flop side-to-side. I added a rear strut across the bike frame and a pair of lengthwise plastic (acrylic?) struts to stabilize the packs.
A pair of padded clamps holds the crosswise strut to the bike frame and a washer captures the rear fender’s mounting bracket.
Looks hideous, works fine.
The black tit hanging down from the strut clamp is a bit of heatshrink tubing that cushions the kickstand when it’s up; otherwise, it rattles against the stub end of the aluminum rod.
Yeah, the bike’s pretty grubby. I’d rather ride it than wash it… and, anyway, I follow my father’s advice: “If you have to move it to clean behind it, don’t move it!“
I have a pair of underseat packs on my Tour Easy that have sagged rather badly over the years. That might have something to do with the fact that my toolkit and other odds & ends weighs more than some bike frames; while I don’t need that stuff very often, it’s good to have around.
Tools & suchlike live in the left-side pack, the near one in the photo, and you can see the problem. The right-side pack holds HT batteries, my belt pack, and other relatively lightweight stuff; I’ll fix that one when I see whether this works. The panniers at the rear wheel are for groceries and other bulky items. The trailer, well, that’s how we do groceries…
Broken Pack Backplate
Anyway, the underseat packs have a black plastic (styrene?) backing that cracked under the stress of the stuff inside, allowing the top corners to cave in and the bottom to droop.
The hooks holding the pack to the underseat rack were riveted through the backing sheet and the hardware, but a couple of good shots with a punch broke them free.
Some rummaging in the Parts Heap turned up a big acrylic sheet (“100 times stronger than glass!”) that’s absolutely the wrong material for the job: it’s too brittle. However, I’d like to see whether a stiff backplate will solve the problem or if I’m going to have to get ambitious and build an internal pack frame.
Acrylic Plate and Aluminum Stiffener
It’s essentially impossible to get a picture of a project built largely from acrylic sheet, but here goes.
I traced the outline of the old backplate onto the new sheet’s protective paper, introduced it to Mr Belt Sander to get those nice round corners, then drilled the holes. It turns out to not be quite symmetric, so there’s a right way and a wrong way to insert it into the pack.
All the hardware is stainless steel. They used aluminum rivets, which is the only reason I could punch them out without too much difficulty, that I’m replacing with SS 10-32 machine screws & nuts.
The aluminum stiffener is a random chunk of ribbed extrusion from the Heap; the original was almost exactly twice as long as one backplate, so the two halves (one for the other pack) are precisely right. I milled out the center rib around the nuts to get enough clearance for a nut driver.
Stiffener Hardware Detail
Herewith, a closeup of the hardware. There’s an acrylic sheet in there, honest, it’s under the aluminum extrusion and fender washer. Really!
I put an automobile license plate in the bottom of each underseat pack to act as a floor for all the crap inside; it’s an almost perfect fit and should give you an idea of the pack’s size. It also maintains the bottom’s rectangular shape and keeps heavy stuff from sagging; there’s a hole scuffed in the bottom from the intersection of a high curb and just such an oversight.
Tour Easy Underseat Pack Detail
Having washed the pack while it was apart (there’s a first time for everything), it looks a lot better than it did before. The yellow block in the front pocket is the kickstand plate mentioned there. It used to have a mesh pocket along the side, too, but that snagged on something and got pretty well ripped, so Mary trimmed it off when she sewed a patch over the aforementioned hole.
It’s still saggy, but the top corners of the plate are holding it up a lot better now. If they crack again, I might just have to go with some aluminum sheet.
These packs seem to be obsolete. The ERRC Lloonngg panniers (search for them) seem to be, well, too long for most purposes; they look as though they would interfere with ordinary rack packs. If I were doing it over, I’d look into hacking a pair of smallish duffel bags.
The Smell of Molten Projects in the Morning 