Nice.
I would add that it shouldn't be much of a try and error for the pattern, but plain geometry.
Figure 3. An ideal representation of a two-, three- and four-stranded rope laid with a pitch angle corresponding to the maximally rotated zero-twist structures with the respective pitch angles of 39.4°, 42.8° and 43.8° relative to the equatorial plane. With these pitch angles, the strands will neither rotate in one or the other direction under vertical strain.
Table 1. Pitch angle, vZT, for the zero-twist structures given as a function of the number of strands. For the zero-twist structure there is no coupling from strain to rotation. Further, to these helical structures one cannot add additional rotations.
No. of strands 1 2 3 4 ∞
vZT _ 39.4° 42.8° 43.8° 45°
http://iopscience.iop.org/0295-5075/93/6/60004/fulltext/http://iopscience.iop.org/0295-5075/93/6/60004/pdf/0295-5075_93_6_60004.pdf So for a two stranded rope you would only need to draw a helix with a 39,4° pitch angle.
To make a good representation of that, the function plotter extension would come handy, plotting a sin wave. Only needs some scaling since without it would show a 45° pitch angle (scale down the height with 82,141% ?). Adding the right stroke width is the only hard part.
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