Author 
Comment/Response 
Andrew

02/28/12 09:40am
Hey all,
I'm Andrew, 2nd semestre mechanical engineering at ETH zurich. Sorry for my english, it may not always be correct. This week we had a little entering in Mathematica in our Ingeneertools section.
There for as final work we're building a planetary gear animation for various radius and angular speed. So far so good, I could do almost everything on my own until one little problem (wasted over 16h yet with that .):
To do the choppers of the gears, I need a Do[] function to multiply each chopper(chopper=disk[]). This comes inside my Animate[Show[Graphics[{...}]] function.
a chopper looks like this:
Disk[{Sin[2*t + k*(2Pi/9)] + Cos[2*t + k*(2Pi/9)]}, GZahn]
Now I do a Do[] function to get my 10 choppers:
Do[Print[Disk[{Sin[2*t + k*(2Pi/9)] + Cos[2*t + k*(2Pi/9)]}, GZahn]], {k, 0,9}]
If I put this into my Animate[] function, it doesn't draw me the disk but open a message board and write it in there.
If I just copy all the outup into my Animate[] function, it works perfectly. But I need it for various amount of choppers. So I did research and tries till I almost died ^^, tried it with e.g.
Do[CellPrint[TextCell[Disk[{Sin[2*t + k*(2Pi/9)] + Cos[2*t + k*(2Pi/9)],"Input"]}, GZahn]], {k, 0,9}]
but this just writes it as input at end of Animate[] and not inside it so doesnt draw my graphics. I tried it with different brackets and quotation marks, with functions like InputForm, Evaluate, Write, Sow, Throw.........and so many more.
Then I got one little step forward with (all in one cell):
m = 3;
Do[funktionxyz[k + 1] =
Disk[{Sin[2*t + k*(2 Pi/9)], Cos[2*t + k*(2 Pi/9)]}, GZahn] +
funktionxyz[k], {k, 1, m}];
funktionxyz[m]
The output of this is:
Disk[{Cos[\[Pi]/18  2 t], Sin[\[Pi]/18  2 t]}, GZahn] +
Disk[{Sin[2 t], Cos[2 t]}, GZahn] +
Disk[{Sin[(2 \[Pi])/9 + 2 t], Cos[(2 \[Pi])/9 + 2 t]}, GZahn]
So it's right, but the "+" should be a ",". I tried hours again with quotation marks, &&, ;, [],{},(),'',/[RawComma],/[InvisibleComma] to get that *** comma in, but every of the tries gives me errors in the Do[]
function.
Now I can't anymore, burned out of motivation and energy and hope you can help me. I mean in PHP, Java, C++ it would be sooo easy, just put the For[] in and declare where to do it. I don't know why this isnt possible in Mathematica, to put the Do[{k,0,10}]{..........................} and just put for every k inside brackets and fine...
Rly appreciate every help TY ;)
Andrew
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