More Steering

Now what I need to decide is how to mount the steering mechanism. Options:

1. The easy way, relatively speaking, is to cut out the steering system from the old bike and affix it under the seat. Unfortunately, the old bike's head is longer than the space where it needs to go, so this is out.
2. I could cut off the top of the old bike's head. This would allow me a solid steel cylinder to put the yoke into, and a system of bearings to make it turn easily. I would need to devise my own way to keep the yoke from pulling up out of the head, and I would lose some of the anti-wobble effect of the longer head. Not sure the impact of losing the bottom system of bearings, beyond these two. Also, the yoke is too long for the space, and would also have to be shortened.
3. A variation of # 2: I could cut out the middle of the head, and attach top and bottom together. Would give me the bottom bearings, but would make the head a weak-point. All I could do to join them would be to apply epoxy, and this might also compromise the free turn of the handlebars.
4. Find a smaller head. The main problem here is the hassle and cost.
5. I could attach the handlebars to a perpendicular pole, then put a simple pin through the pole, and be done with it. Say, use a short bolt, one of those quarter-inch ones that has a length without threads. There'd be more wobble than either of the above, and it wouldn't have the bearings to turn so nicely around, so precision, high-performance steering is out. But it's by far the simplest.

Steering

There are two basic formats for steering that I can think of, illustrated in the diagram above. The green bar is the handlebar, the blue dots are joints, the red are steering bars. The triangle represents the stem of the yoke that turns the wheels, in black. The handlebar turns about its center, not marked.

The first thing I think about them is that the push-pull format seems to work best when the steering is significantly behind the wheels, although I have seen other designs that use the lateral design from behind, and use a bent bar (the long red one in my diagram) to reach the wheels.

I think the real difference is the travel, how far you turn the handles to turn the wheels. I think the push-pull method would make the wheels turn quickly with very little motion of the handlebar, not a good thing. In the lateral method, the shorter the little bar (red) that connects the handlebar with the long red bar, the longer the travel of the handlebars.

It's also the method I've seen on pro trikes.

How much bike to use

Today's question is: do I cut off the entire rear triangle of the salvage bike, or do I only use half of it? That steel is heavy! Moreover the connection into the main bike is tricky, since I foolishly did not leave a long tail on the lower pole, and the bracing poles interfere with connection parts.

I have long tails on the upper two bars. This is what I leaning toward: I will use half the lower bar of the triangle, connecting the cut-off ends to a bamboo fork I can splice into the main frame. I will use the entire rear bar of the triangle, to have the mounting space for brakes and other items. The tails of the upper bamboo can make nice lap joints with the rear triangle bar. The bamboo, with a little shaving, can fit into the cut ends of the lower bar. A little diagonal bracing and this should be a strong mount.

Joinery Experiment

I just tried both the methods listed below (Joinery 2 & 3). For the hanger-bolt joint (joinery 2), I omitted the epoxy, since I hoped to reuse the materials. For the mortise-and-tenon joint (joinery 3) I used a piece of 1/8" ply cut in a modified rectangle for the tenon and bamboo skewers for pins. The modification was essentially a tail, an extention of the rectangle at a width slightly less, so that it could slide inside the cavity of the crosspole, giving more pinning length while requiring the bamboo to be cut less.

Hanger-Bolt Joint
Joining caused splitting of the hardwood dowel, and subsequent stress and splitting of the crosspole. Joint was not square. No problems with compression of the bamboo from the bolt. There was minimal wiggling in the joint, but when I applied pressure the screw of the hanger-bolt pulled out of the dowel, due to its split.

The non-squareness of the joint was likely due to the difficulty I had centering the hole for the screw-side of the hanger-bolt, and making the hole perpendicular. Also, I did not perfect the curvature of the crosspole cut to fit the main pole. The splitting dowel was encouraged because of the difficulty getting a snug fit between the dowel and the bamboo cavity.

Also, screwing in the hanger-bolt is challenging.

Mortise and Tenon Joint
Fitting the mortise-and-tenon to each other was easily done with a dremel. Getting a tight fit was not difficult (the hanger bolt pulls the parts together in the other joint, in this joint this must be done manually). Pins held without glue. The resulting joint was square with minimal wiggling. However, when force was applied, the wiggling gradually increased. Eventually, pins cracked, one failed entirely, and the tenon tail split off.

Conclusions
I like the mortise-and-tenon joint, despite its failures. 1/4" ply and larger diameter pins (bamboo chopsticks? wood dowels?) will improve strength. Epoxy in the joint will not only give adhesion, put will also fill gaps and minimize the wiggling. Triangulating joints will also minimize wiggling. If wiggling can be eliminated, the progressive growth in wiggling should also disappear.

Most important, of course, was the ease with which I was able to get a good-looking joint. Precision is not a strength of mine, so any method that doesn't require me to hold my drill perfectly vertical is a better method.

The Motor

Many of you may be wondering about the motor:

That part is simple. I buy a wheel with a motor attached, put it on the bike, and I'm good to go. A number of good motors are made:

Bionx
Electric rider

I think I'm going for the Phoenix Cruiser from Electric rider, because it is fast (30mph), but has more power for hills (important in Vermont) than their faster Racer model.

The Bionx system has regenerative braking, which I like, but it also has a system to prevent the bike from exceeding 20mph, which is the legal maximum, yes, but... when's the last time you bought a car that couldn't go faster than 65?

Steering mechanism

Another decision was how to rig the steering when your technical skills are limited. Most Tadpole Trikes (two front wheels) use a design where the crossbar of the frame heads out toward the axle, then has a hinge. This is clearly the superior design, but I don't know how to find such a hing. I don't think door hinges will work. So my thought was to take the front end of a pair of kid's bikes, and have the crossbar connect to the cylinder.

• Use a bike with a small front tire, say 16", so your bike doesn't look like this:

The downside is this involves a bamboo-metal connection, but we'll deal with that in a bit.

Trike: one in front or one in back?

I knew I wanted a trike so I felt safe on slippery roads, so it felt more car-ish. I bike is simpler but I wanted a trike. However, trikes do have a stability problem. The traditional trike design, called a "delta," with one wheel in front, can easily flip at high speeds. This illustration shows why:

A. Trike moving forward. Blue arrow indicates interia keeping it moving forward.

B. Front wheel is turned, creating a deflection force (pale blue) for the front of the trike.

C. The trike starts to turn. Inertia still wants the trike to move forward, the wheel is still deflecting the trike front to the right. Notice that inertia is now moving across the line between the front wheel and the rear left wheel. This line become a fulcrum for the bike to tip over. In a car, the weight of the car is shift to the front left wheel. In a delta trike, this wheel doesn't exist.

D. Inertia keeps the bike moving forward, by adding a simple torsion to the bike mass, known in highways safety lingo as a roll-over, or just a crash.

In a trike with one rear tire and two front tires (called a "tadpole"), the left front tire does exist, and the rollover is prevented.

Other factors, pro and con:

• A delta trike requires a more complex power train, some sort of differential to allow the rear tires to spin at different rates in a turn, and or a single axle to transmit power to both tires.
• A tadpole trike requires a more complex steering mechanism, so the front wheels turn in unison.
• One poster has said that tadpoles are more inclined to fishtail.
• The majority of trike designs available from more technically informed people are tadpoles.
• Tadpoles look cool.

I'm gonna make a tadpole.

Frame Design

I really know very little about bamboo as a building material. Exactly how thick a pole of what species do I need? My cursory research didn't reveal "how strong is bamboo" so I did what Idle Dads do, which is to get some and see. I need to keep costs down, but I figured that, depending on what I found, I could probably adapt the design. I ordered 1" dia. tonkin poles from http://bamboofencer.com/, which doesn't have surcharges for small orders and ships from nearby Massachussets.





Here are the three basic frame designs:

The Single Pole, or cross design, is what to use if the bamboo proves very strong and sufficiently rigid. In the picture above, the rear wheel is on the long end of the cross, the front wheels on the ends of the crossbars, and the crank and pedals on the bent tip (the crank needs to be above the seat, for various reasons).

The Double Pole design should be much stronger, and stiffer in the vertical dimension. Not shown in this sketch are short lengths of bamboo connecting the two principal poles. The weakness of this design is that there is no stiffening in the horizontal direction, nor from twisting. This means loss of some of the shock absorbency of bamboo, and some wiggle in steering. It is possible to put the two poles side-by-side instead of over-and-under, which would restore the shock absorbency and stiffen the steering, but the trade of would be loss of strength in the vertical direction. Since this is the direction of stress from a pothole hit at 30mph with 180lbs of Idle Dad aboard, it would seem to be the primary need for extra reinforcement.

The Triple Pole design is stronger in all directions. I can't imagine that it won't be strong enough. It loses some shock absorbency, and it is significantly more complex to build than the others, but is the assurance that my 1" poles will be adequate. The picture above may be tricky to see, but I am finishing a model that I will post soon.

Metal, Plastic, or Bamboo

Everyone else makes them out of metal. But to do metal you need to weld or "braze" pipe together. Before I started this project I'd never even heard of "brazing." Another posibility is ABS pipe, like water pipes are made of nowadays. I decided against plastic for several reasons:

• I don't like plastic
• It gets brittle in cold weather and I live in Vermont
• I've heard complaints about how it weathers

I wasn't sure if the bonding in plastic weld--adequate for carrying water--would be adequate for carrying 180# of Idle Dad 30 mph over potholes.

Bamboo suggests several advantages to me.

• It looks cool
• It's natural flexibility will provide shock absorbancy over frost heaves.
• I read about how to do bamboo joinery and--unlike brazing--it sounds like something an Idle Dad can do.
• It is a renewable resource and doesn't offgas solvent vapors
• I've always liked bamboo

As you can see, my resources are all based in good engineering and sound logic