Peter Nunn wrote:

Cannot remember the exact details but I remeber that the rotor (choroid ?)
is made by revolving a circle whose circumference is 1/3 of a second

circle

around the inside of the larger circle, while the housing (epichoroid ?)

is

drawn by rotating the smaller circle around the outside of the larger
circle.  Obviously the shapes are the track taken by one point on the
smaller circle.

Wrathall Mark wrote:

Thanks Peter and Vance for the answers.  I don't have Qbasic and would
really like to do this in AutoCAD (V14). I found the calculation for the
epitrochoid housing on a link from Monito.com, isn't the internet a great
thing. Shame Felix didn't have access, as it could have save him a lot of
time figuring this out.:~)
http://iae.tdec.drexel.edu/Computer/MAPLE/Maple_4/Wankel_Engine/epitrochoid_
derivation.html

r = 1
s = 2
h= 0.5
For t= 1 to 360
x = (r+s)*cos(t) - h*cos((r+s)/r*t)
y = (r+s)*sin(t) - h*sin((r+s)/r*t)
Plot (x,y) (Actually it would need to be a Pline or Spline command
Next t

How do I convert this into a  lisp routine? I can draw in AutoCAD, but am
not familiar with LISP programming.

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