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Wednesday, June 7th, 2017 12:21 pm
At some point in the late 90s I got interested in railbikes. Picked up a book on the subject, thought a lot about how I would design one, put the idea in my personal warehouse 23 of never-started projects, and forgot about it.

Until last year, when I noticed an abandoned rail line along my bus route was looking particularly evocative. The county had recently bought it, and was converting to trail usage a bit at a time. So if I was going to do something with it, I had a deadline.

Other projects got in the way, of course, but in March of this year I finally got started. It should have taken under a month, but now that I have a more or less complete machine shop, I can actually make things perfect. I should probably develop an immune system response to this trend, but not yet.

I set 3 goals for the project:
1) Fully convertible between rail and road usage. Everything needed to fold up and lock in a storage configuration with a minimum of fuss.
2) The bike in road mode had to fit on a city bus bike rack.
3) When I was done, I'd make a grand multi-modal expedition. Bike down to the bus stop on 520. Take the bus over the lake to the railhead, then bike on the rails from Kirkland down into Bellevue. Where exactly I'd end up I wasn't sure, as I carefully resisted looking up the route the rails took.

Because I wanted a fully convertible bike, I had to go with one of the classic railbike designs. Ride on one rail, with an outrigger running over to the opposite rail. Attach a front guide to the fork of the bike, with top and side rollers to hug the rail you're riding on. This lets the front wheel of the bike track the rails, and the rear wheel just follows along. As long as the front guide doesn't jump the track, everything is fine.

First step was to work out spacing for the front guide. I made a simple gauge out of the roller skate wheels I planned to use for the guide and went to the tracks. I quickly realized that, with the ugly cable connections bridging all the rail joints, the rollers could never be in constant contact. Best would be to make them adjustable, so I could dial in the spacing on the final version.

So I got a bit fancy in CAD and came up with this. Fully adjustable side wheels, both up and down. And since I couldn't resist, the in-and-out adjustment is automatically symmetrical, thanks to a double-ended screw. Yay left-handed threads!

And... it worked! For the first time in my life I can design something exactly how I want, and then actually made it. No fudging. No ugly angle-grinder cuts, nothing awkwardly filed to size. Bolt holes that perfectly match, without having to be drilled out a bit. The top roller axle is even held in with snap rings. Nothing is hacky, not even a little bit.

With this part done, it was time to get serious. So I bought a classy beach cruiser from a Goodwill and set to work. The outrigger was never as elegant, sadly. Spanning the sacred distance four feet eight and one half inches (praise be to Trevithick and Stephenson) meant using a lot of standard tube stock, and a lot of welding. To compensate, I got even more finicky about the front guide.

I decided to pivot the guide fork from the hub of the front bicycle wheel, so I made a set of nuts and screws. These replaced the existing hub nuts, which were the wackadoodle size of 3/8"-26. That's a tap/die set I doubt I'll ever use again! But I didn't care, because I got to use the collet block on the mill to cut perfect hexes for the wrench to grip. I really love using collet blocks.

(At this point I went through a series of 3 test runs with the bike on real rails. Most of the problems that came up weren't very interesting, but...)

On the second test run, I was able to bike for a good kilometer or so. And then I came, to use the proper Sorkinian expression, to an abrupt arboreal stop. A broken branch laying down next to the rail had caught the side roller, bending its mount and almost throwing me off the bike. Whoops.

In response, I made those mounts much beefier. I also got a bit Mad Max about protecting the side rollers, as obviously it was better to push debris away from them in the first place.

I also upgraded the clamp which held the front guide onto its fork to the v3 design. This included making a big custom knob to let me adjust the angle. More lovely collet block work!

The last problem to be solved was how to hold the front guide in the upright and locked position for road usage. This had to leave enough room under it for the restraining arm of the bus bike racks to clamp down on the front wheel. I finally came up with these clips, to be welded to the handlebars. They grabbed the front fork with the perfect snickt. So satisfying.

Of course, they weren't really done until I'd made another set of custom knobs for locking them down.

And with that, it was time for the expedition!

In short, it worked great. And I was completely exhausted by the end. (That last pic was from my perspective as I decided that some ballast in the shade made for a perfectly serviceable couch.) Pushing through the vegetation was the worst, but the front guide handled it like a champ. Never jumped the track, even when blackberry vines got wrapped around a side roller and I failed to slow down.

Final modality review:

Road bike: A-. Heavy, and a bit hard to mount, but generally just fine.

Rail bike: B+. It worked, but still some things I'd like to improve, like preventing the front guide angle from drifting down over time.

Bus: C. Very awkward to lift into the rack, due to the weight. And I removed bits to reduce the alarming wobble at freeway speeds on the way home.

Walking: A+! (The tires had gone flat by the time I got home, so I had a surprise 4th modality to test.) The folded up outrigger actually makes a great handle for walking it. Normally I find the seat uncomfortably low to hold onto, and using the handlebar means the pedals keep clipping my ankles. This was by far the nicest bicycle walk I've ever experienced.
Friday, June 9th, 2017 04:25 am (UTC)
Or a cam attached to the fork at the hub. Or even one on the roller mechanism.