Lights for a beater bike

December 23, 2013

A first effort at writing this up, if you’re interested and it’s unclear, ask questions.

I’ve never been 100% happy with the packaging on home-made lights, but glueing power LEDs to aluminum angle iron with a mirror on top works pretty well and gives you some options for mounting (for example, using long bolts to bell brackets). On a bike with a front basket, however, the basket itself is a natural place to mount not only the light, but also most of the wiring, so inferior packaging is not such a big deal.

To start, here’s what the bike looks like with lights installed, showing the basic arrangement of the basket, hub, wires, and tail light.

Beater bike with hub-powered lights mostly mounted under Wald basket.

Note that there’s no off switch and no way to disconnect anything but the hub without wire clippers or a soldering iron. Why build it like this? #1, eliminating connectors and switches eliminates sources of failure. #2, daytime running lights turn out to be useful. From the OECD, Cycling, Health and Safety, p. 170 (pdf):

The safety effect of daytime running lights on bicycles was tested in a Danish study in 2005 (Madsen 2006). Nearly 2,000 cyclists in the town of Odense used the new induction lights (flashing type) for one year with, while 2,000 others continued with ordinary bike lights, which were only switched on during dark hours. The accident frequencies of the two groups (based on self-reported accidents) were then compared and analysed. … The main result was that use of daytime running lights was associated with a reduction of the number of crashes by more than 30%. The number of related crashes (crashes in daylight and with a counterpart) decreased by 50% approximately. Both results are statistically significant. There are indications that the study may have not controlled for all factors – for instance it is unclear to what extent the control group’s crashes included single vehicle crashes (this type of crash is hardly influenced use of induction lights). Also, the study makes no finding as to the safety effect of flashing versus steady lights.

The photo below shows the basket from the other side, and on Flickr it is annotated with notes on some of the parts, but the basic idea should be clear; there’s room under a basket, and plenty of stiff wires that can be used for mounting zipties. The little wooden stick is intended to adjust the level; ideally some of the light is visible to approaching traffic, but it is better if most of it is kept down low and out of people’s eyes. One problem with “beater bike” systems is that it’s not clear how much money to put unto them; for another $25, it’s possible to add a second set of LEDs on a switch that are aimed lower and with a color chosen not to be so deadly to night vision (e.g., amber, or perhaps warm white).

Side view of LED lights under Wald basket

The photo taken from below in the front shows the LEDs, lenses, mirror, wiring, and aluminum angle on which the LEDs are mounted. Note that one lens is a spot, and the other spreads its light out horizontally. The goal for the spread lens is to ensure visibility from the sides and to fill in the near part of the road.

Headlights and mirror

The “better taillight” is made from stuff I had lying around because “you never know, that might be useful”.
The clear tube is acrylic with one-inch inner diameter, and the round top is an acrylic hemisphere, held on with superglue. There’s a fancy holographic diffuser film in there from a sample sheet; not clear that is really necessary, some vertical sanding on the inside/outside of the tube might have been just as effective.

Better taillight.

Front LED: could be CREE XTE, XPG2 or XML2.

Rear LED: could be red or red-orange. Red-orange is a fudge to make the taillight be slightly brighter, but the modern red LEDs are probably adequately bright. It’s even possible to use deep red.

Lenses: Taillights don’t need lenses, but headlights do. I like to use a spot for one and an oval for the other.

Lense holders are necessary for the headlights and their lenses.

PCB for rectifier/doubler.
Or this improved PCB for rectifier/doubler.

Diodes: SB540

Small capacitors: 1000 uF, 16V

Large capacitors: 6800 uF, 35V

Wire: I use marine-grade, 2-conductor, 18 gauge.

Mirror: 1/8″ Acrylic mirror from US Plastic

Acrylic tube

Acrylic hemisphere

Assembly hints/gotchas:

First cut mirror and aluminum angle. I sized the aluminum to fit to one side of the support under the basket — the middle seems symmetrical, but it will get dirtier there. Next drill aluminum. Next glue mirror to aluminum, then drill through mirror. I always roughen surfaces before gluing and use 5-minute epoxy because I am impatient.

It’s good to clip the LED hexagons to a heat sink while you are soldering them, except for the tab being soldered. That protects the LED from being overheated (I ruined one that way once, though I didn’t ruin about a dozen others being careless).

Use nail polish on all the exposed electrical connections (but not on the LED lens itself) to help protect against the elements. It’s not required, but it helps.

Glue the hexagons and lenses in one operation, clamping the entire assembly. The lenses have a larger diameter than the LED pucks, this prevents you from gluing them on too close to the mirror. Be aware of the orientation of the oval beam lens — you want it wide from side to side, not from top to bottom.

Work some tape in around the headlights to help keep water splashes off the LED.

When wiring, always think about strain relief. Vibration on a bicycle is the enemy of all electronics, including wires.

The taillight is always ad hoc and depends on what your mounting options are. Gluing hemisphere to tube uses superglue in a pretty large quantity, and the superglue vapors tend to fuzz the acrylic surface (which is okay for a taillight). A bare LED works, but a little protection from bashing and the elements is better, and a larger-than-point light source is also better.

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