[python] Re: RWS Python

  • From: Rhisiart Gwilym <Rhisiart@xxxxxxxxxxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Tue, 29 Mar 2011 07:13:09 +0100

Siwmae Pawb!
I've always taken the working definition of a FWDRWS as being that the rider sits on the front end of the bike, with the steering articulation under or just behind him/her. In this way, the whole rider-capsule (if you want to enclose it as a velo) is kept narrow; no need to give extra width to the nose of the capsule, to accommodate sideways-swinging feet. 

Also, this arrangement seems to eliminate PSI.
Dennis Renner seems to have accomplished the -- supposedly non-doable -- practical, easily-rideable FWDRWS bike, especially with his Mark 2 version. He never mentions any particular difficulties of riding. See his vids!
BTW, Dennis sent me a couple of photos of his Mark 1 and Mark 2 bikes, both shot from the side, so that anyone wanting to copy his ideas can pick up the general geometry pretty accurately. He tells me that the pivot angle on his Mark 2 is 71 degrees, and the videos suggest a pretty sweet, easy rider.
Incidentally, I've argued for some time that, realistically, the Mark 2 is actually a centre-steer, rather than an extreme RWS, but with the articulation right at the back of the centre section. That's a bit nit-picky though, perhaps. The real acid test, it seems to me, is whether the rider sits on the front or the rear section. The articulation is under the rider's backrest on both of Dennis's bikes. 

Hwyl fawr,   Rh


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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