So does anybody have a drawing or better yet 3D model of standard
 rotor? If not than we'll have to wait for Paul to produce one.
             Thank You  Ted

 Does anybody know how to calculate the radius of the rotor face?

  Paul  Lamar



    Hey all,

    Here is the excel file I have been working on. It is not finished and I
    am still sorting out a couple errors here and there but it is getting
    there. Eventually the thing will be all correct and allow you to change
    the
     variables and do all sorts of neat stuff. I just got laid off
    recently from Delphi (note: F*%k the American auto industry) and have
    been busy with finding a new job so I will get back on it when I get the
    chance. Paul, note that the rotor equation never nets a constant radius.
    This data while representative of the the points cannot be used in a
    machine shop environment. This is where my questions of Solidworks 2009
    came from as you would need to graph the sketch of the equation and not
    a spline of a number of points. I checked with NX3 platform and SW2009
    and it looks like they are too simplistic to do what pro-e does. Who has
    pro-e that we can test out? I can gpo
     more into it at depth but will
    only do so if there are serious questions about it. Here are a couple
    things that will show you whats up with what I mean. I am working
    diligently to get this worked out because if my plan for a lightweight
    all steel
     brazed rotor works out then I can move to the next step which
    is increasing the capacity of the engine and and having the weight of
    the rotor as the cast iron version for the larger capacity engine be the
    same as the 13b/renesis. 8500rpm to 10000 rpm limit on a 1 liter rotor.
    That sound intersting to anybody?

    http://www.profilesmagazine.com/p33/marsalek.html

    http://esoxrepublic.com/blog/category/geometry/splines/

    http://www.adras.com/SW2009-Equation-Driven-Curves.t8302-83.html

    Rob Woods

    If I am understanding  you correctly you are saying the face of the rotor is a
    not a circular arc?

    Paul Lamar


Paul,

The statement I made before is true.You can see by looking at the
graphical output on my program that the curvature in somewhat flat in
the middle where the combustion chambers are in comparison to where the
apex seals are where the equation starts to take a swooping turn which
increases the curvature. There isn't a solid radius arc anywhere in that
equation. Kenichi Yamamoto wrote the book with all the derived and
integrated formulas that net the equations of the inner housing and
rotor. If it was a simple as drawing three circles and trimming the
outside stuff I think it would have been written as such. Any attempt to
look at it so simplistically without actually taking the time to work
out what he provided us is a fools quest to put it lightly. So sagitta
has nothing to do with this. This all comes back to what I have been
speaking about. I can set up 1080 points or many times that number and
import that into solidworks and run a spline through it all. A curvature
comb placed on it will show all sorts of weirdness going on. Getting an
accurate cad profile is priority for this since any custom housings or
rotors need to be spot on for any number or reasons. There are a couple
programs that can do this and with some resourcing I can get the
profiles into Solidworks.This board is one of the resources I have and
hope that someone can work something out with this. Or someone who is
much better/smarter than I in programming Macros I can install into
Solidworks. I have one so far but havent verified the accuracy yet.

One thing that I think might be a constant arc is the side seals. They
are not an offset of the rotor profile which makes me wonder why for one
and also because how they might manufacture them. Constant section large
diameter that gets cut into three pieces maybe? Is that the reason for
not being a offset of the rotor surface?

Rob Woods

You are absolutely right. My mistake.
I have no doubt what you say is true. I happen to know however the rotors
have been machined three at a time on a turn table. I have a picture around here someplace of the machine. I think it was a Curtiss Wright machine. This is what fooled me.

Obviously Mazda is not doing it this way unless there is something hiding behind the turn table. I did not see the machine used when I was in the factory but Mazda would not let me take pictures of that part of the plant anyway. It is not an NC machine as the plant was built in 1969.

I laid a rotor on a piece of paper and traced the face curve.
An arc with a 9.15 radius comes pretty close. Here is a scan of the paper.
My 715 mm (28 inches) radius number was way wrong. I am not sure why. The arc radius is more like 9.15 inches. This is something everybody can try.
This also proves your contention.

Here is the fly in the ointment. All these engines require a depression
in the face of the rotor to form the combustion chamber. What only matters is the exact path of the apex seals. I contend a pure triangular rotor with straight sides would work. The compression ratio would be too low but the engine would run. I contend an arc of some radius with a combustion chamber depression would be close enough.

Interestedly enough here is a patent on a CW rotor face that did not come close to an arc.

BTW Ansdale published the math in his book "The Wankel RC Engine" in 1969.

Paul Lamar