[python] Error in Last Calculations -- YDiff numbers were too big
- From: Michael Rienstra <ageless@xxxxxxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Wed, 15 Sep 2004 09:33:16 -0700
Hello All,
Just a quick follow-up to my last big long VPS* post, in reference to
the trailing edge of the front tire (TEFT) hitting the front of the
seat when steering sharply -- I really don't think that this will be an
issue with any of the four bar linkage geometries, because the arc that
the TEFT moves through is pretty flat. I was getting worried about
having to make a gap between the seat and the TEFT to allow for a lot
of movement, and I started playing with one of my models, and noticed
that the TEFT was moving sideways much more than back. So I reread my
last email and realize that I defined Y as the shortest distance along
the y axis between G and C, which was pretty silly -- it should be the
shortest distance along the y axis between G and the midpoint of C (not
exactly TEFT but close enough!), because we're not worried about C the
coupler link colliding with the seat, but rather the wheel (TEFT). So
here are the proper numbers for YDiff, using the proper definition of
Y:
Narrow: YDiff = 0.7 cm - 3.3 cm
Square: YDiff = 0.8 cm - 1.8 cm
Short: YDiff = 1.5 cm - 3.5 cm
But even with the Short geometry, the TEFT moves sideways much faster
than it moves back -- 9.3 cm along the x axis at 20 degrees for the
Narrow geometry, and 5.7 cm along the x axis at 20 degrees for the
Short geometry. So as long as the front of the seat has a gentle curve
(like most recumbent seats, to make it easier to put your feet down),
there should be more than enough room for the TEFT to move around, even
if it is very close to the seat when the steering angle is zero.
Michael
*VPS = Virtual Pivot Steering, maybe not the best abbreviation since a
bike company is already using it for "Variable Point Suspension", and
acronymfinder.com list 25 different uses of VPS (computer folks know it
as Virtual Private Server)! How about VHT for Virtual Head Tube? We
should settle on something so it's easy to refer to the design, like
FWD for front wheel drive or SWB for short wheelbase. Maybe VF =
Virtual Fork? Naa... VPS seems like the best thing... I'll use that
until someone comes up with something better.
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