Non collapse of the Sinha spectral sequence for knots in R^3

We give an explicit description up to the third page of the Sinha homology mod 2 spectral sequence for the space of long knots in ${\mathbb{R}}^3$, that is conjecturally equivalent to the Vassiliev spectral sequence. The description arises from a multicomplex structure on the Fox Neuwirth chain complexes for euclidean configuration spaces. A computer assisted calculation reveals a non trivial third page differential from a 2-dimensional class, in contrast to the rational case.