Sept 8

Sept 8, 2004

Ugh! I just spent two entire days fabrication a steering system that does not work.

The steering bar is good and I can use that, but I'll need to solve some other steering problems first. Basically, the way the steering works is a steering bar that pulls cable through sheaving and pulls part of the frame to one side or the other. The prototype used cable and pulleys and worked quite nice, but I wanted to try cable and sheaves this time to simplify the whole thing. I'm pretty sure I could just use break cable, but I used push/pull cables from a throttle control instead - same 1/16" steel cable but slightly thicker sheaves.

There are two clamps - one on the pivot tube and one on the pivot head tube. The sheaves but up to a plate mounted on the head tube clamp and the cable terminates on the pivot tube clamp. When the steering bar is turned right, it pulls the cable attached to the left hand side of the steering bar which pulls down the right hand side of the pivot tube clamp causing the bike to lean to the right. Visa versa for left.

After a quick test, I determined that it just didn't work. It required WAY too much effort to initiate any kind of turn at all, so obviously I have my leverage all wrong. I calculated that a full 3 inch movement of the steering bar would cause a total of 3 inches of movement at the back, but I think working with dimensions that small cause undesired aspects of the whole system to be exaggerated.

So, I'll scrap the whole rear clamp assembly and invent something with more leverage.

Here is how I made a plastic head set for the steering bar - Instead of a standard bearing, I used UHMW plastic which some say will out last most ball bearings. UHMW is a high density plastic that resists water, acids and most chemicals. It's non-toxic, unbreakable, easy to work with and has an ultra-low friction, non-scratching surface which makes it idea to use as a bushing that can replace a bearing.

1. I cut a 3 inch chunk out of the Plastic UHMW loaf

2. Since the ID of my headtube is a bit less than 2", I drilled out a 2" dowel

3. Then I machined the plastic dowel down to the same inside diameter of my headtube, plus 1 mm for a press fit and left a 1/4 inch shoulder at the end.

4. What I should have done is bored out a hole to fit my steering tube with the lathe, but I'm borrowing the lathe from Ben, and can't figure out what tool to use. So, I drilled it out with the drill press (not nearly as accurate, but I got lucky and the bit diameter happened to be very close to my steering tube).

5. This shows the assembly - I did the plastic bushings in two parts, each with a small shoulder that is the same dia as the headtube. Then I hammered each half into it's respective side of the headtube and slid my steering tube in.

The steering bar is held in place on the bottom with a washer and a cotter pin.

On the top there is another washer and I welded a clamp to the steering tube where the steering bar clamps into.

The action is smooth, but slightly more firm than a bearing and equally as rigid.



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