Perp fram changes

Hello again, One question, I have a curve that, with rotation cero has a perp frame in a direction and when i move the slider, the perp frame changes, so in cero degress i have to look at it in top plane and the rest of angles in front. I want always to be valid in front plane, (20.7 KB)
anybody knows why? Thanks a lot

Check these two methods. (30.9 KB)

Thanks a lot!!! But you know why it happens?

and another question, the y vector you put in the cross product, it is always positioned at the begining of the other vector b? Thanks!!!

You can find the direction of the cross product by the right-hand rule.