Moonraker: the prototype that bit back
I love a good rough prototype
As a user experience designer, I love simple, ugly prototypes that efficiently test one part of a design. In my most recent personal design project, a prototype came close to killing me. Fail often to succeed sooner? Not like this, thank you.
Crunch
I was almost into the Guerrero street intersection last Saturday, just before Thanksgiving, when the front wheel of my bike came completely off. I went from smiling to shocked, then stunned as my front fork, no longer held up by the wheel, dropped and planted itself in 22nd Street. My 200 pound, 6' 2" body flew over the handlebars and slammed into the pavement. I heard a surprisingly loud crunch as I landed, and some pedestrian’s gasp from the sidewalk as she watched me do my endo.
After a very short experiment
It was dusk, I had ridden approximately 500 feet. The first test ride of the project I’ve been working on for a month or so. To put a motor on a bike strong enough to enable me to pedal up the steepest San Francisco hills without breaking a sweat.
For a moment, it felt amazing. The motor made a quiet whirring sound, and helped me move along. I still had to pedal, but I could ride faster with much less effort. But only for a moment.
As I lay on the pavement hoping I didn’t have internal injuries, other than bruised ribs, a few scratched knuckles, I thought, I’m lucky, and then I’m stupid, because I already knew what had happened.
All the torque of the new front-wheel mounted electric motor was being applied to the four thin steel faces of the dropouts that held my front wheel in place. This twisting force had pried the drop-outs apart slightly during my short ride. This caused the wheel to twist itself free from the bike, causing my shakedown cruise to end violently. This is a well-documented hazard for aluminum forks in the online electric bike forums. They break like the picture above. Since my fork was steel, I thought I’d be safe.
So much for rapid prototyping.
My vision: e Fixie
This started because I wanted a commuter bike that I would ride a lot. Our San Francisco streets are anything but smooth, and I didn’t want to get shaken to pieces on every ride. I didn’t need track performance, but I did want a beautiful bike.
I thought about converting a fully suspended mountain bike into a commuter bike by putting street tires on it. But I find these high-tech bikes to be heavy looking, overly complicated, and ugly in an urban setting.
I love the circles-and-triangles profile of road bikes. The mechanical greyhound esthetic that makes fixies so beautiful to look at. However, riding them is frequently a jarring experience.
Made of steel
While I looked at the amazing amount of information on endless-sphere.com, I realized my late-eighties Univega proto-mountain-bike, might make a great electric bike: It is steel, which I learned is more pleasant to ride than aluminum, and is strong while also being flexible enough to deal with the kinds of loads a motor would put on it.
With big tires
There’s a resurgence of wide tires on road bikes because research shows that on rough pavement, skinny tires like you see on many SF fixies are actually less efficient than wider tires. And wide tires offer a smoother ride.
German tire manufacturer Schwalbe is driving this trend with its balloon road tires, which are being adopted by dozens of European bike makers. One US bike designer who has designed some exceptionally beautiful, high performance bicycles with big tires is Paul Budnitz.
I ordered a pair of 60mm (very balloon-y) tires from Amazon, and put them on my Univega’s rims. I thought it looked amazing. Like something you’d ride around on the moon. Moonraker is born.
To make it more fixie-like, I replaced its 10-speed derailleur with an 8-speed hub, and removed the front derailleur. This gave it a simple chain line from the pedals to the rear hub. It was starting to look like I wanted it to look.
And a motor
There are a few bike makers selling motor-equipped bikes that look beautiful, like The Urban Factor in Munich. Also the Faraday inspired me, as did IDEO designer Purin Phanichphant’s home-made e-fixie, which was also an inspiration to the Faraday team. But none of them are available to buy in a store yet. And I’m a designer, why not DIY?
There are many many small manufacturers in the US who will sell you a motor kit, and you can even buy the parts directly from China over the internet if you like. I got mine from one of the more gonzo kit purveyors in the US: Hi-Power Cycles, after seeing its Youtube video of a rider summiting Eldred Street in Los Angeles without pedaling. None of these kits is particularly well thought through or refined however.
Why not just pedal yourself?
When I exert myself any more than a brisk walk, I feel a funny prostaglandin tickle in my skin and I start perspiring. A lot. I’d like to use a bike to get places in San Francisco. But I sweat so much people either think I’m weeping, wet myself, or it is raining outside when I show up at a meeting. And since the city is hilly, I have to ride slowly to keep from getting completely drenched. And if it is warm out? Forget it.
We won’t work on it
The day before my crash, I’d dropped off Moonraker at the excellent Valencia Cyclery shop to have them re-align the front brake now that the motor-equipped wheel was in-place. I can do this work myself, but I thought that having a pro tune the brakes before Moonraker’s maiden powered run was a prudent investment in insurance.
As soon as the mechanic saw the motor on the front wheel, she said, “We won’t work on that bike.” She didn’t like the look of the motor, and said that the front axle wasn’t fixed well enough in the dropouts for her comfort. She was concerned the shop would be liable if I got hurt.
I told her she was being judgmental. She relented after I pleaded politely, and agreed to tune up the brakes.
The accident happened less than three minutes after I rode off the next day. She had been right. Why? I had made the decision to omit a crucial part from my design: a torque arm. Which a conventional bike mechanic wouldn’t know was missing because it is a part specific to e bikes.
The $5 torque arm
I am not the first experimenter to be thrown head-first from my bike. Apparently this type of failure is common as electric bike motors have become more powerful. People have died in similar accidents to mine. But luckily, the solution is simple: prevent the axle from spinning by anchoring it with an arm that attaches to the fork and distributes the twisting force. This gives the axle something more substantial to push against, preventing it from spinning freely or wiggling out.
The leading online purveyor of torque arms is the amazing Grin Technologies in Vancouver. I’m waiting for one to arrive in the mail as I type this. If you’re considering doing a similar project, I’d suggest buying your parts from Grin. They’re awesome engineers and evangelists for powered bicycles.
Prototype #2 next
As soon as the new torque arm arrives, I’ll install it, and write another, hopefully more victorious installment to this story.
Prototypes are supposed to be safe ways to fail fast. This one wasn’t. Do you have any stories about prototypes that bit back? You can leave comments over on Google+.
