Friday, February 17, 2012

A new bicycle headlamp design: philosophy and rationale

In my opinion, contemporary bicycle light offerings have not kept pace with the demand for classically inspired bicycle components.  Companies like Velo Orange, Rivendell and now Compass Bicycles have fed demand for newly manufactured retro-styled components to update vintage frames as well as to equip the growing number of available lugged steel frames inspired by classic touring, randonneuring and racing bicycles.  These 'modern classical' builds can now be built with new handlebars, brakes, levers, rims, cranksets, saddles, stems, racks and fenders, all conforming to the new retro aesthetic defined mostly by Velo Orange and Rivendell.

However, contemporary headlight offerings that match a modern classical build are limited.  The best, and most popular option is the Edelux by Schmidt.  I have one on my 1970s Holdsworth Super Mistral and it is a great looking and performing light.  Its polished aluminum finish certainly agrees with the modern classicist's backlash against anodizing of any kind (here, the other major boutique player, Supernova, falls short).  The light is diminutive (85g!) and the hemispherical design is certainly better than anything else out there, vaguely reminiscent of the Soubitez 'golf ball'.   Still, in my opinion, it looks a bit out of place on a vintage or modern classical build.

Other contemporary offerings in the vintage vein include the Lumotec Retro and the recently introduced Classic from Busch & Müller.  The Classic is chromed and has a nice retro-looking selector switch, but on the whole I think it's one ugly duck.  The Retro is a little better looking than its younger sibling. I used to have one and it is just a Lumotec halogen lamp with a chromed plastic shell to retro-fy it.

After that your options are limited to a handful of cheap chromed bullet lamps from Taiwan or you can hunt down a vintage French headlamp, something I used to do with more enthusiasm before increased demand drove up Ebay prices.

I'm forever experimenting with upgrading vintage bike lights with modern LEDs and optics, but these efforts have led to me to conclude that the best option for a modern build would be a completely new lamp designed from scratch.  Something bright, elegant and weatherproof.

So, I designed one, hereby christened the 58A. 

Nº58A headlamp

This design references the elegant teardrop shape of the classic French lamp makers like Radios, Luxor, Soubitez and JOS, which were made of spun aluminum.  The lamp housing, bezel and bracket will be CNC machined and, of course, it will have a modern LED with standlight.

Nº58A cross section

Good thermal management is crucial to LED performance, so the LED is mounted on a large copper heat sink that transmits heat away from the LED through the lamp housing.  My design is for a dynamo powered lamp to begin with but the Cree XM-L can be driven up to 3A, so a battery powered version (with an external battery pack, unfortunately) is an option down the road.  The heat sink is very likely up to the task.  The reflector is, out of necessity, an off-the-shelf model designed for use with Cree XP LEDs. The beam is tightly focused but with enough spill to provide good off axis visibility in traffic.  I haven't done a detailed analysis of the beam shape but it reminds me of my Supernova's beam: round and symmetrical.  A reflector that produces an asymmetrical cutoff beam like that of the popular B&M IQ reflector is not available in the format I need.

Nº58A dimensions

The headlight is on the larger size, about 58mm (2.3in) at its largest diameter and 77mm (3in) long, though still smaller than classic French teardrop lamps such as the Radios Nº18 and the Luxor 65.  It's also quite hefty; based on volume and material density calculations, around 228g or 8oz.  Almost certainly too heavy for fender mounting (at least without a second set of stays), but fine for mounting on a front rack or fork crown.  The weight is due to a combination of thicker walls than traditional spun aluminium and the dense copper heat sink.  One advantage of the thicker CNC fabrication is that it shouldn't dent like old spun housings.

A friend of mine kindly put together a few photorealistic views in polished aluminium:

You can see the complete set here on Flickr.

Noticeably absent from my drawings is a switch. Finding a place for a power switch has been the most challenging design issue.  Vintage French lamps were almost universally bottle dynamo powered, precluding the need for a switch.  There isn't a compact enough selector switch available to mimic the switch of the old Sturmey Archer headlights.   I contemplated something similar to the clever magnetic reed switch used on the Edelux, but that design requires custom plastic parts.  In the end, I decided to go for a short actuator toggle switch with a splash proof boot. You can see its placement in the following renderings:

Shown is a switch with a flatted actuator, but I'll probably use a standard round actuator as it fits better in the boot and creates a better seal.  The seam between the lamp housing and bezel will be sealed with silicone grease and an o-ring will seal between the bezel and glass lens.

At the moment, I'm finalizing a quote with a prototype maker.  With a prototype in hand I'll be able to spend the spring and summer riding with it, running it in the shower, hitting it with a hammer, striking it with lightning, etc, etc.  Then, if there's enough demand, I might consider doing a small production run.  I'll post updates about the project here.   If you're interested, please comment below or send me an email (address at bottom of page).  I've even reserved a name for this putative enterprise: Bici Lux.

Friday, February 10, 2012

Free CAD software: 3D, 2D, and PCB layout

I rely heavily on CAD freeware for all my weird obsessive bike light projects.  Never having been a professional engineer or designer, I haven't had the luxury of being able to snag a copy of any commercial CAD software from my workplace.  Licenses for such things run into the thousands of dollars (I emailed Solidworks a few months ago to get a quote for an individual license for hobby use and they asked for a cool $2000).  No thank you!

It took me a long time to discover the tools that I use to design parts in 3D, draft them in 2D, capture schematics and layout PCBs.  Here's a list of the free CAD software I find most useful:


Man, I really like this software. If you're a CAD veteran you might hate it but for the beginner I don't think it could get any easier than this.  The software is specifically for designing single machine parts and the design restrictions do a good a job of preventing you from designing something that can't be machined.  Living within the software's rules can be a frustrating limitation at times and I'm often forced to think outside the box (so to speak) to design a specific feature on a part  (cutting a feature out of a solid, for example, uses a kind of confusing 'air inside/outside' paradigm).  It kind of forces you to think like a CNC machine, which is no bad thing if you want your part design to actually be machinable.  Making parts by revolving a profile is very straightforward.  The autosnapping is fantastic - no key combinations are required to snap to midpoints, endpoints, centers, tangents, etc.  Best snapping interface I've encountered, allowing me to work fast.  However, complicated parts with many surface features on different axes are not this application's forte.  If I need to do more complicated Boolean shaping then I modify my part in FreeCAD.

eMachineShop wants you to use their machining service and there's a handy online quote generator that allows you to get pricing for different materials and tolerances.  For pieces out of steel and aluminium, I find their prices competitive with other big online CNC services like QuickCut and Firstcut.  All three online machine services quote about 1.5-10 times higher for the same material than most of the prototype makers I've contacted in China.  I've used eMachineShop's fabrication service once and was disappointed with the quality of the material and the use of an inferior machining method (plus they initially over charged me for shipping - $128 UPS to Canada!).  The part was within tolerances and performed its function, but eMachineShop's off my list of prototype makers for now.  Most folks report a good experience, so I'm aware that my dissatisfaction was an exception.

To their credit, eMachineShop's CAD software allows you to export 3D IGES files as well as 2D DXF files.  The 3D export has a disclaimer that it's still a work in progress, but for the most part the original design survives the export.  For some reason, adding holes to curved surfaces starts to screw things up, a problem that can be solved by modifying the part in FreeCAD.

Although I haven't used it, eMachineShop does support CNC bending, so you can design parts bent out of sheet metal.  Unfortunately, the bends are not exported in the 3D IGES file, so you wind up with a flat version of your part on export.  I'm not sure if the .igs file plus a 2D description of the bend locations, their radii and angles would be enough to get a quote from a third party fabricator.

I love it and hate it. It's deep but challenging.  For de novo part design of anything but the most basic fundamental shapes, I stick with eMachineShop and then modify the part in FreeCAD.  For the most part, I use FreeCAD to make part assemblies so I can see how everything fits together.  The Boolean operations are good for cutting one complicated shape from another, something that I can't do in eMachineShop.  FreeCAD is still under heavy development, which means it can be a bit buggy and frustrating to use sometimes.  It has a small community of enthusiasts where you can get help. The forum is particularly valuable for finding scripts to make complicated features that would be difficult or impossible to do with just the GUI.  A helical thread, for instance.  FreeCAD looks and feels very promising, but the frequently buggy Boolean operations and a lack of complete GUI implementation of all features is holding it back from a wider audience of prospective users.  For my purposes, though, it is perfectly adequate.

One feature I've discovered recently is the Drawing Module, which lets you generate 2D drawings of your part, including isometric views.  The GUI implementation is almost nil, so you spend a lot of time manipulating objects by command line, but the results are pretty cool:

Taillight concept 3D
Taillight 2D isometric view

The results of the isometric projection can be cleaned up with DraftSight.

Prototyping services seem to like IGES format for quotations, so I use IGSViewer to check the outputs of both eMachineShop and FreeCAD to make sure nothing wonky has happened during export.


A new piece of software for 2D drafting, it is quite deep with a reasonably good interface.  Like eMachineShop, the implementation of snapping to endpoints, midpoints, tangents, perpendicular, etc. is very handy, although you need to turn it off if you don't want to snap to the nearest feature, no matter how far away it seems.  I usually import the DXF output from eMachineShop into DraftSight where I can build up my 2D drafts.  The isometric views that FreeCAD spits out in .svg format can be imported (via InkScape) and cleaned up to produce pretty nice looking technical drawings.  Dimensioning is pretty straightforward, although I often wind up fighting with the global attribute system.  For freeware this is very well-developed. Not sure the story behind it.  Perhaps it's just intended as a halo application for its super expensive big brother, Solidworks.


Big freeware competitor to Illustrator. I've only used it to convert .svg to .dxf for FreeCAD drawing import into DraftSight, but it looks pretty cool.  I've never been an Illustrator user, so I don't imagine using his much, but it sure is handy for the very specific file conversion I need to do.


Eagle CAD

This software is an electronic hobbyist's dream come true.  I found the learning curve a bit steep, but once you get it Eagle CAD becomes a great all-in-one schematic capture and PCB layout application.  There is a good tutorial from Sparkfun to get you started. The large libraries of components never seem to have the specific parts I want to use, so I've had to get used to designing my own schematic symbols, laying out the pads according to the datasheet's description of the device's footprint and adding the part to my own custom library.  This is kind of a pain in the butt, but I guess you can't expect the libraries to be completely exhaustive.  The freeware version has a limited board size (plenty of space for what I want to do) and only supports 2 layer designs (the PCB house I use only offers 2 layer fabrication). The autorouter seems to do a good job of routing the connections after placing the parts. I typically don't route manually, instead shifting parts around until the autorouter hits 100%.  In the world of PCB design, that makes me a bit of a loser.  So be it.

I'm sure I'm missing out on other great CAD tools. Let me know what your essential pieces of free CAD software are.

Monday, February 6, 2012

Classic bicycle taillights

Luxor Le Martelé taillight. Photo by J Ferguson
I love classically styled bicycle taillights, especially those of the French persuasion.  I have a handful of Luxor tail lamps waiting for the right project to come along (yes, I'm the type that would build a bike around a taillight).  I just discovered this gallery on Flickr dedicated to curating photos of both vintage and handmade taillights.  As well, there's this great Japanese site that has examples of classic lights from Radios, Luxor, Soubitez and JOS.

Unfortunately, modern taillights are invariably plastic and utilitarian in nature.  Compass Bicycles had a recent post bemoaning the indifference to elegance in contemporary taillight offerings.  If you want a nicely designed light suitable for your modern classical build, you're looking at acquiring something vintage (these options from Kimura notwithstanding). If you're into classic randonneuring bikes, then vintage options can get very expensive.

Although I'm partial to the fender-mounted teardrop-shaped Luxor lights, I also really like the JOS tail lamps, especially the Fu model.  Here is a beautiful example from Flickr:

JOS Fu taillight. Photo by spoke sniffer.

It occurred to me that the symmetrical design would lend itself well to CNC machining. For fun I drafted up a concept:

This would obviously be equipped with an LED, so the protruding bulb holder with it's knurled binding post isn't required, although it might be nice to incorporate it.  The bracket might be a bit of a challenge to have made, but the body could be turned on a lathe without much trouble.  The lens, on the other hand, would have to be injection molded, which is associated with high setup costs for unrealistically large volumes.  Perhaps a 3D printer could produce something that might work.  For now, my classically inspired taillight design will have to remain in silico.  What do you think? Does the world need a new taillight?

Friday, February 3, 2012

Ledil optic improves Sturmey Archer Cree XM-L upgrade

I recently posted about a Cree XM-L upgrade I designed for the vintage Sturmey Archer head lamp (at least the one seen most commonly on North American Raleighs from the 1970s).  The light output is high, but the beam shape has some significant shortcomings, rather embarrassing ones considering the centre of the beam from the original bulb was still brighter than the LED upgrade.  Yikes!

The wise and wonderful people at CPF suggested I try a small modern optic instead of relying solely on the vintage reflector.  The choice of sub 20mm optics for the XM-L is quite limited.  The best I could find was this 16.1mm  37º optic from Ledil (This 23º optic would probably be better but wasn't stocked by either Mouser or Digikey).  It arrived from Mouser today.  I had to snip off the mounting posts, but it otherwise fit perfectly over the XM-L's PCB, attached firmly with its own adhesive tape:

Ledil 16.1mm 37º optic mounted on XM-L
As before, I measured the beam profile at 2.5m from my lux meter's sensor.  Here's the data I would show if I was a savvy marketer:

Beam profile of Cree XM-L with Ledil optic compared to original incandescent bulb
Well, that looks great.  Big fat wide beam compared to the puny and narrow beam of the original bulb. Of course, that doesn't tell the whole story.  Here's the same beam profile compared to not only the original but also to a 0.35A incandescent.  The profile of the untreated XM-L's beam is also plotted:

Beam profiles of Sturmey Archer lamp with different light sources
While the Ledil optic does a nice job of evening out the profile of the XM-L's beam and doubles its brightness in the center, the peak output is still a lot lower than a simple incandescent upgrade.  Granted, an original Dynohub barely puts out 0.35A at high speeds and the front bulb is usually run in parallel with a 0.1A taillight bulb.  What you get from the Cree XM-L is a bright wide beam with lots of spill.  This results in a nice amount of off axis visibility, which is important to me in the city traffic where I do most of my riding.

With the Ledil optic I'm willing to declare my Sturmey Archer LED upgrade a success.  There's even the possibility of upgrading to the 23º optic if it ever makes its way over to North American shores.

Wednesday, February 1, 2012

Incandescent optics versus LED optics: implications for upgrading vintage lamps

Sometimes facts get in the way of a great idea. I've devoted a lot of time to the problem of upgrading vintage lamps to power LEDs. Power LEDs produce a ton of light, but they get hot and require adequate heat sinking to maintain their output and limit the chance of failure. This led me to develop a series of rather elaborate copper heat sinks. I've made a screw base LED bulb, a wedge base LED bulb, and custom LED heat sinks to fit the classic Sturmey Archer headlight as well as the Luxor 65 series of vintage French lamps, all using Cree XP-G or XM-L power LEDs.  I fired them up from both a DC bench top supply and a hub dynamo and I was impressed with the results.  For the Sturmey Archer and Luxor headlamps, the outputs were bright, producing huge floody beams.  Before I could make claims about the superiority of these upgrades, though, I thought I should take some lux readings and compare the output of the LED upgrades to that of the original incandescent bulbs.

Cree XM-L mounted in Sturmey Archer headlight

Here is some lux data comparing the output of an original 6V bulb at 350 mA (in actual fact, the original bulb was 6V 0.2A with a parallel 0.1A taillight bulb), a 3W halogen bulb (Reflectalite GH106) at 500 mA and the Cree XM-L upgrade at 500 mA (low end modern hub dynamo output) and 700 mA (high end hub dynamo output as well as Dynohub magnet upgrade).  Lastly, I measured the output of a Cree XP-G mounted in a 41.5mm reflector designed specifically for Cree LEDs. The lux meter's sensor was placed 1M away from the light source and the centre hot spot of the beam was measured.   The lux reading recorded represents the brightest spot of the beam.

Lux output of Sturmey Archer headlight with different light sources compared to Cree XP-G with specialized reflector

Well, what the heck?  Is ancient technology really winning?  Well........... yes, in a nutshell, it is. :(

Although I haven't photographed the beams, allow me to emphasize how different the incandescent/halogen beam patterns were compared to the LED patterns.  The hot spot of the incandescent/halogen beams that yielded the highest lux reading was very concentrated. The slightest change in position of the beam could see the lux reading tumble by half or more; the focused hot spot was very small and the overall beam was quite narrow, certainly less than 45º.  In contrast, the LED upgrades mounted in the same reflectors produced a very diffuse hot spot and a very evenly illuminated flood of probably greater than 120º.  The LED upgrade is clearly putting out more light, but it isn't focused like the incandescent bulbs.

To document this quantitively, I placed the sensor of my lux meter on a tripod and focused the center of the beam on it (highest lux reading).  I then took readings at finite distances from the centre of the beam while maintaining the same distance from the light source, essentially creating a brightness profile across the beam's diameter. I rather arbitrarily set the distance at 2.5m.  Some bike light makers measure performance by lux at 5m.  Lux at 1m also seems to be a common standard, however I was limited by the distance between my work bench and my wall, so 2.5m it is, which is fine for a relative measurement.  Here I compare the XM-L's beam to the beams of a 6V 0.35A incandescent as well as the 6V 0.2A incandescent that originally equipped the Sturmey Archer lamp.
Brightness profile of Sturmey Archer headlight beam with three different light sources

As you can see, both incandescent bulbs produce a narrow symmetrical beam that drops off to zero between 40-50 cm from the center.  The 0.35A bulb has a surprisingly bright peak, whereas the original 0.2A bulb is considerably dimmer. The XM-L beam doesn't have much in the way of a center peak, but provides a wide profile of even illumination.  Unusually, it seems to have some asymmetrical artifacts, which I confirmed by measuring the beam in a different axis (not shown).  My room wasn't big enough to measure the full width of the XM-L's beam.  If was able to, I expect the area under the XM-L's profile curve would be a lot larger than the area under both incandescents' curve (ie. greater total light output).

The 0.35A bulb isn't an especially fair comparison as the original configuration was a 0.2A bulb, however it does indicate that a simple incandescent upgrade can dramatically improve the light output. Although I didn't measure the beam profile, you can bet that the 0.5A halogen bulb would be even brighter!

The obvious problem with the XM-L's performance is the optics. The vintage optics are optimized for incandescent bulbs.  The limited viewing angle of the LED means that, although a lot more light is coming out of the lamp, the optics aren't focusing it into a tight beam.  I had originally fretted that the LEDs weren't in the right position relative to the vertex of the reflector's parabola, but changing that position doesn't have much of an effect on beam pattern.  The glass globe of an incandescent lamp allows the filament's light to enjoy a greater than 180º viewing angle. It is my suspicion that it is this backward directed light that is collected and focused by the reflector.

This LED/incandescent performance difference is less pronounced with the Luxor 65 reflector.  Interestingly, the results indicate that the Sturmey Archer lamp does a considerably better job of focusing incandescent light into a tight beam.

Cree XM-L mounted in Luxor 65 head lamp

Lux output of Luxor 65 head lamp with different light sources
So, I think the lesson to be learned here is that there are rather strict limitations to what you can accomplish with a LED retrofit of a vintage lamp. You really are at  the mercy of the reflector, which does a surprisingly good job of focusing a small amount of incandescent light into a tight beam, but isn't very compatible with the narrower viewing angle of power LEDs.

It also really emphasizes how deceiving lumen ratings of LEDs can be.   I suppose this is why Maglite uses 'Beam Distance' to measure the performance of their flashlights rather than total light output or lux at a finite distance (1m, 5m, etc).  This is the maximum distance at which a light source will produce 0.25 lux, thus taking into account both the total light output and the throw provided by the optics.

Modifying or replacing the reflectors of vintage lamps isn't especially practical, so I think I've hit a performance wall here.  While the LED upgrades don't produce a tight focused beam, their output still produces a bright flood that is certainly adequate for riding around town at night and maybe along a dark bike path at normal speeds. I haven't done a side-by-side comparison yet, but I'm pretty sure the greater total light output from the LED upgrade will result in greater noticeability in traffic.  Careening down a long hill on a moonless night on your vintage French randonneuring bike is probably not advisable though...

The bright side (forgive me) to all of this is that the rear red LEDs are much much brighter than their original incandescent counterparts.   I fret constantly about being visible from behind when I'm riding, so I'm more concerned about having highly optimized lighting for the taillight.  The LED upgrade offers a bright standlight and a super visible rear light (with the potential to flash!), which, for my purposes,  makes up for the fact that the head lamp beam pattern is less than optimal.

Still, hope for a better beam shape is not lost.  The opening into the reflectors of both the Sturmey Archer and Luxor lamps is less than 20 mm, but there are modern plastic optics with a diameter less than that.  It's possible some modern optic made for the XM-L might improve the beam shape.  This one from Ledil looks promising:

Ledil Cree XM-L 16.1mm optic
Need to order a couple of these and see if they can improve the beam shape.

Update:  optics arrived and the results are pretty good.