grasshopper field lines force spin direction

hey guys,

I'm working with magnetic field lines in grasshopper. some are affected by a force spin.

my problem is, i want the lines to be affected by different spins. means some turn in one direction, some in the other.

if I create force spin, I'm not able to change the spin direction.

Is there a way to solve this problem? I already tried flip, negative, e.g.

I took some screenshots to explain.

Any ideas? Would be really helpful! need to solve this tonight :(

Thx a lot for any ideas!

valerie

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Bildschirmfoto%202016-06-28%20um%2022.28.53.png

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magnetic.grid.spheres.gh