Hi
I have been thinking for a few years of building a bike using a 4-bar type
pivot. My idea is to use two sets of 4-bar pivots, one above the other.
That way the virtual steering axis could be located in space by the two
virtual pivot points. I would like to make the bike so that the attachment
points for the links could be adjusted for width at both ends. In that way
the virtual steering axis could be inclined at any desired angle and at any
distance in front of or behind the front wheel (within reason). In one
bike, one could have a virtual python, a vitrual Tom Traylor style bike or
indeed a RWS bike (depending on your definition of RWS!).
Mike Channon
London, Ontario, Canada
At 09:40 AM 3/28/2011 +0800, you wrote:
Hi Vi,
I had seen this one before. The whole blog about this construction can be
found there (in french):
http://velorizontal.bbfr.net/t7559-tad-le-znb
In fact, this is not a real pivot, but a trapezoidal mechanism (two
nonparallel pivoting bars connected to the rear wheel axis on one end and to
the frame on the other end), creating a "virtual pivot point" towards the
front. (If the bars are parallel (making a rectangle), the virtual privot
point is set to infinity and the rear wheel is just translated (offset to the
left or right) without modifying its angle, whereas if the two bars connect to
the frame at the same single point (making a triangle), this point is the (now
real) pivot. Any configuration in between (making a trapeze) displaces the
'virtual' pivot point in between...) Somebody else has made some 3D graphics
and movies about the same (as well as another similar) mechanism:
http://oliviercresson.free.fr/s4bc.htm
So actually one might not qualify this as RWS as the effective pivot might
actually be located close to the front wheel. As somebody suggests in the
blog, though, what might matter for that definition is more the main weight
distribution. Debatable and debated...
I also think RWS is in principle a good idea, but it might be tricky to find
good configurations for easy rideability (whatever one means with that - the
french guy from the video comments that he is the only one so far able to ride
his bike. Of course, a matter of training, but also perhaps a 'mother-child'
love and determination relationship? :)
I'd be interested in your results should you try to make one of these!
Regards,
Pascal
p.s. sorry for the empty posts - I am not sure why my emails to
python@xxxxxxxxxxxxx usually bounce back to me with freelist management
instructions?
On Sun, 27 Mar 2011, Vi Vuong wrote:
This one (znb) seems quite controllable, pivot slightly pointed to the
rear,
and trail ~zero or negative, and probably gigantic turning circle.
http://www.youtube.com/watch?v=SGlNhdxesbc&feature=related
A RWS python should retain the best features, hands-free, self-centering,
low...
RWS seems more difficult because of no direct control of both wheels like
the
FWD version by the body / legs. However, if it works, we can gain quite
a few
benefits - less PSI / speed, positive trail, bigger front wheel, lots of
space
for pivot behind the seat and even handle bar... Should I give it a try?
Vi
[python] Re: dennis renner
* From: Dirk Bonné <dirk.bonne@xxxxxxx>
* To: python@xxxxxxxxxxxxx
* Date: Thu, 23 Sep 2010 07:25:52 +0200
The experiment is as follows: hold rear part vertical and turn the front
part ->
on a python we get seat rise. But if we hold the front part vertical,
then turn
the rear part, then the seat will lower on a python. On a RWS the bulk
of the
weight is on the front part, so leaning of the front part on turning will be
small (to balance we need to shift weight). So from this assumption there
would
be no self centering effect on dennis bike (and the cal poly bike it would
have). Dirk
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