ProjectVF - March 1st, 2008
The Test Mule was originally
designed to experiment with different rake and trail settings. At the time I
used a simple drag link to connect the handlebars to the fork, as shown at
right. It worked OK for the rake and trail experiments, but won't work for
the prototype. The existing steering (salvaged from a little girl's bicycle)
can be easily changed to test new ideas.
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With the Test Mule I can try different pivots and connecting rods to determine what works
best. The simple drawing at right shows a potential combination which I can
make cheaply using wood and common hardware. With a little time and testing,
I should be able to find a workable compromise, then adapt it for a sturdier version on the
prototype itself.
Doing a fast-n-cheap mockup is what I should have done last time, but was in
too much of a hurry which led to failure.
The steering mechanism is a daunting task. Consider the scale model at
right. The mechanism can't block the space above the engine because that's
reserved for the carburetors and air cleaner. It can't block the rider's
knees, can't allow any bump-steer feedback from the suspension, and most of
all, has to remain a 1:1 turn ratio.
These are the sketches I built from. I printed a rough drawing, then added
notes and dimensions. Next I hand-drew another version with detailed notes
and used that to begin fabricating.
Here's how this steering prototype turned out. I used a combination of go-kart rod
ends, cheap bolts for pivot bushings and plywood for the rest. A little
welding was required, and some sawing, but it only took about two hours to
make.
Here's a close-up showing how the handlebar is connected to the upper drag
link and rear pivot with a welded bracket. The plywood pivot is connected to
the frame with a plywood bracket. My total expense for this was zero since I
recycled existing parts and raw materials.
Here's a nice side view of the Test Mule with the prototype steering
mechanism complete. I tightened everything as much as possible to reduce
slop, then pushed it up a local hill for a couple test runs. As expected,
the control felt a little loose and vague, and it seemed to turn left easier
than right, but the basic design works. Next will be some analysis,
some fine-tuning, and another round of test runs which hopefully will lead
to a sturdier, all-steel version on ProjectVF itself.
