.setRotationFromMatrix( ); - what causes the mirroring and thus the flickering?

Here Struggling with paths - #5 by hofk I have a perfect motion along the curve. It used CurveModifier and so it works only for meshes.

Here Struggling with paths - #7 by hofk I tried to make it for a model. A few variants. But not the solution.

After that I tried to solve it with quaternions. I could not determine the appropriate formulas.

With matrices it gives simple formulas. With tangent, normal, binormal and Matrix3 and Matrix4

M3.set( );
M4.setFromMatrix3( M3 );
object.setRotationFromMatrix( M4 );
object.position.set( )

The curve is taken into account exactly, but there is a running reflection and consequently a flickering. See MovementOnCurve

What am I doing wrong here?

Again and again, it’s the little scampers with which I make things difficult for myself.

n.crossVectors( t, b.negate( ) );

.negate( ) was missing.

Now it works. Link see above.