Friday, February 1, 2008

The Bamboo Trailer

(Originally posted 12/11/07)

Okay, this is the story of how I built the Carry Freedom Bamboo trailer.

(Go look at the trailer, then come back. You need context. Context, I tell you!)

The Art Building at UH Manoa (where I go to school) decided to cut down its bamboo. My friend who has a class there noticed this and saved a lot of it for me. We sorted in into appropriate sizes (6' approx. for 2 of the bits and 4' for most of them) and I went to the hardware store in an attempt to find the rest of the bits.

The bolt/nut combinations were straightforward. I already had a drill, so that was the obvious choice. $1 each or so, and I used 1 from an old trailer I had around that I didn't like.

The axles were -- and remain -- the great difficulty. The Carry Freedom plan calls for a machined assembly to connect the axle to the trailer. It looks really cool. I didn't feel up to making it, so I made a couple of different attempts.

The trailer, when completed, is huge. A 4' x 4' bed doesn't sound gigantic, but it is.

This is the Official List of Innovations:

1) Axle assembly innovations -- first we tried using pipe attachments and homemade spacers. This was simply not a good idea, and repeated failures convinced us of this. A couple variants on the theme were tried, and they were all bad. Our current setup uses two scrounged bicycle forks as holders. This works reasonably well, but it is not as structurally sound as the original Carry Freedom design and they add both weight and additional bits that are only mostly attached. I am looking into how much it would cost to have the parts machined locally, and when I'm a little better off will maybe just have that done. This attempted innovation and its many failures was the cause of many lost hours and about $10 in used up materials.

2) Found bamboo instead of bought bamboo. On the one hand, I saved $20-25 and am super environmentally awesome. On the other hand, warps in the bamboo caused some needs for a workaround, and one of my bamboo poles is just a little too small to be structurally sound. If I had it to do over again, I'd compromise -- buy most of the frame and use the found bamboo as a bed.

3) The hitch -- Carry Freedom has a machined hitch, and it attaches to the rear axle, which is less than optimal on my bike, as I don't have derailleur spring thingies to handle small changes in tension. My hitch is composed of an old garden hose, some leftover bamboo, and some pipe clamps to hold the bike end onto the bike. It's reasonably easy to take on and off and seems quite sturdy. I think this is the one main innovation that's maybe worth keeping.

4) The size -- the thing is freaking huge; cutting a foot off of the width (leaving it as a weaker rectangle as versus a square) made it far more usable. The length, however, is quite nice. Also worth considering if you build this thing.

The List Of Outright Mistakes: This is stuff that was just done wrong.

1) Got the wrong kind of wire. See the wire discussion below.

2) Tried to attach the axles with nails instead of screws. Just plain a bad idea.

3) Didn't get enough bolts. Don't be a cheapskate. $2 is not worth the extra trip to the hardware store. Oh, and make sure your nuts fit your bolts. That whole coarse/fine thing is not a meaningless statement.

Okay, on to the photo album:

Pic of the raw materials. I was assisted in this by my friends Mitra Salehi (pictured) and Shanta Kaneshiro (wielding the camera and thus largely unpictured).

Mitra working on measurement.

The frame takes shape.

Lacing wire around a center pole -- this keeps the frame from parallelogramming. We had a hard time figuring out how to tension the wires. The original plan calls for two sets of wires, which one uses a stick to tension. Then when the two sticks are happy, one ties them together and voila! But this isn't terribly compatible with a bed. So we used one set of wires. But then there is no way to keep the wire from unraveling. Solution -- I used the cotter pins that came with my previous bike trailer; when sufficiently tight, they could be wedged against the frame (and tied tight with the nylon cords that came with them). Cheap and recommended.

I bought wire that was too big; it was rated for 250 pounds, but that meant it was too thick to tie. So we unraveled it into its separate strands (there were 7 strands, so we split it into 3 bits -- 2, 2, and 3 strands. That worked ok). So don't buy wire that's so thick you can't tie it in a knot. That's the wrong kind of wire.

Here's the first draft of the hitch. Note that it's a bit, um, unstructured. The later draft, shown below, is quite successful.

It has a little wrench next to it for scale. The hose is housed inside a bamboo piece, with a hole drilled through it and the bolt that holds the bamboo on also threaded through the hose. Solid and so far quite successful.

Here is Mitra and I putting the wheels on the trailer. Note the weak axle assemblies. These things just didn't work at all. Well, I guess you gotta try 'em out.

Here we're finishing up our big push to get the basics done before the workshop closed. Overall, we were very tired and ready to go home by the end of this.

I did some test riding, and I found two things were very clear -- 1) my axle assemblies sucked. Hard. They just weren't up to anything. 2) the thing was just unwieldy. I didn't fit in bike lanes or even on large sidewalks. I had to cut it down.

Phase 2 involved work in my garage -- with Shanta's help and documentation, I cut the bamboo for the bed and also shortened the two side-to-side bamboo poles by a foot each in order to make the trailer somewhat less enormous. The pics are currently trapped in her cell phone.

Phase 3 involved tearing out the axles and scrounging two used front bicycle forks (Thank you, McCully Bike and KVIBE) to hold the wheels on. The end result of these two phases was this:

I used rubber tie-downs to attach the forks to the bike. Not elegant, but it worked pretty well. I compensated for the fact that one of the poles was too thin (and thus pushed the wheel outward, causing a wobble) by wrapping a tie-down around it at the point where the axle touched it. This both evened out the wheel and gave the smaller bamboo some much-needed support.

Here's a not-very-good closeup of the new axle assembly.

And now I have a really nifty-looking trailer!

The frustrating thing is, I now am totally ready to build more of these, but of course there's no need. Lemme know if you need me to build you a trailer, I guess.

Wednesday, January 16, 2008

Trailer update

Well, sure enough, the axle assembly failed. After a couple of promising but failed approaches, we attempted to fabricate the axle assemblies in the instructions.

We tried and failed. We tried and died.

Seriously, we just did not have whatever toolset we needed. We brought the plans to a local machine shop, and they gave us a quote of $130. When we demurred, they were nice enough to give us some sample steel squares of approximately the right size. But drilling the holes discussed in the plans was just not possible.

So: our solution:

An A24 joist angle from Home Depot (image borrowed from their site):

The holes there are 1/2", which is a nice size for my 7/16" axles (a standard size).

But! If I mount it below the trailer, it will be hard to secure it such that the wheels don't shift side-to-side. My solution: Mount the wheels above the bed of the trailer, so the axles themselves hold the brackets open, and we can secure it relatively lightly to the bottom of the trailer to keep it from sliding forward and back.

I used some spacers to keep the wheels level, as you can see in this photo:

It works really well. The only thing that went wrong is that I mounted it about 1/4" too far back, so that when there's load (and the bed sinks slightly), there's friction against the back of the frame. That's trivial, though, and check out the load I carried up to my office on move-in night!