SCREEN 12: CLS : WINDOW (-120, -90)-(120, 90): COLOR 7
pi = 4 * ATN(1)


step1 = 2 * pi / 100
step2 = 2 * pi / 1000

r = 12: r1 = 75

t = -1 / 3

FOR j = 0 TO 2 * pi STEP step2

x0 = r * SIN(1 * j)
y0 = r * COS(1 * j)


FOR i = -step1 TO 2 * pi STEP step1
 lx1 = lx: ly1 = ly
 lx = r * COS(3 * (i + t * j)) + r1 * COS(i)
 ly = r * SIN(3 * (i + t * j)) + r1 * SIN(i)
 IF i >= 0 THEN
 LINE (lx1 + x0, ly1 + y0)-(lx + x0, ly + y0)
 END IF
NEXT i

NEXT j


CIRCLE (0, 0), 3 * r
CIRCLE (0, r), 2 * r

LINE (-3, r)-(3, r)
LINE (0, r - 3)-(0, r + 3)
LINE (-3, 0)-(3, 0)
LINE (0, -3)-(0, 3)

PAINT (0, 4.5 * r), 14, 7
PAINT (0, 81), 4, 14



'untill here it draws the maximum possible piston periphery
'(you can play with r and r1 for different epitrochoidal and
'rotor shapes.
'
'the following just make the animation (press ESC to quit)


FOR j = 0 TO 50 * pi STEP step2

x0 = r * SIN(1 * j)
y0 = r * COS(1 * j)


FOR i = -step1 TO 2 * pi STEP step1
 lx1 = lx: ly1 = ly
 lx = r * COS(3 * (i + t * j)) + r1 * COS(i)
 ly = r * SIN(3 * (i + t * j)) + r1 * SIN(i)
 IF i >= 0 THEN
 LINE (lx1 + x0, ly1 + y0)-(lx + x0, ly + y0), 0
 END IF
NEXT i


FOR i = -step1 TO 2 * pi STEP step1
 lx1 = lx: ly1 = ly
 lx = r * COS(3 * (i + t * j)) + r1 * COS(i)
 ly = r * SIN(3 * (i + t * j)) + r1 * SIN(i)
 IF i >= 0 THEN
 LINE (lx1 + x0, ly1 + y0)-(lx + x0, ly + y0), 4
 END IF
NEXT i


a$ = ""

a$ = INKEY$
WHILE a$ <> ""
 IF ASC(a$) = 27 THEN COLOR 7: CLS : END
 a$ = ""
WEND



NEXT j


END