March 8

March 8, 2004

ANOTHER STUPID IDEA

This doesn't work either. I didn't want to give up on the two wheeled pivot concept without one more try. So I thought that if I could build up some speed, then it might be possible to balance with the pivot on two wheels. So, I bolted on my two trike wheels and added a larger 700 rear wheel that was slightly lower than both of the outriggers. That way, I could use the 3 wheeled stability to build up some speed, then try to 'lift up' onto the rear wheel.

Needless to say, it didn't work at all. It simply flopped from one side to the other, never holding any balance in the middle.

Sure looks cool though hey?

I'm going to take a step back now, and focus on the trike version of this pivot bike to see if I can get the turning radius tighter, and increase the stability of high speed turns. To do that, I'm going to further lower the seat (lower C of G), and bring the two rear wheels a bit closer to the front (as per Bob Rohorn's suggestion).

Generally, I am quite happy with how the pivot trike functions. There are some very attractive advantages with only a few disadvantages of going with this approach for the final HPV.

Advantages:
1. Since the front wheel doesn't need to turn on it's own, I can replace the puny wheel with a nice big 650 like the rear wheel. That will lessen rolling resistance, as well as provide me with more gearing due to the larger wheel (a problem with my small wheel). Since the wheel doesn't need to turn, I can overlap the wheel with the cranks, and place the intermediate drive anywhere on the wheel that doesn't interfere with the legs. This will allow me to get the front of the bike as low as possible (the top of the 650 wheel will be the same height as my knees at the maximum peddling height).
2. Better drive efficiency due to a more direct power transfer from the cranks to the fixed drive wheel (no twisting chain) and possibly getting rid of the intermediate drive and going direct to the hub (not sure yet if that's possible due to clashing with my knees).
3. A better and more natural turning 'feel' where I lean into a steer.
4. Superior stability of a 3 wheeled vehicle over a two wheeler in windy conditions.
5. Less riding fatigue due to the increased stability of the three wheels.
Disadvantages:
1. Additional weight of the three wheels as compared with two wheels
2. Additional weight of the entire pivot structure as compared with a conventional trike (or even a two wheeler)
3. Increased surface area and cross section due to the wide two wheeled rear means less aerodynamic efficiency.


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