  We report the study of a new experimental granular Brownian motor, inspired
to the one published in [Phys. Rev. Lett. 104, 248001 (2010)], but different in
some ingredients. As in that previous work, the motor is constituted by a
rotating pawl whose surfaces break the rotation-inversion symmetry through
alternated patches of different inelasticity, immersed in a gas of granular
particles. The main novelty of our experimental setup is in the orientation of
the main axis, which is parallel to the (vertical) direction of shaking of the
granular fluid, guaranteeing an isotropic distribution for the velocities of
colliding grains, characterized by a variance $v_0^2$. We also keep the
granular system diluted, in order to compare with Boltzmann-equation-based
kinetic theory. In agreement with theory, we observe for the first time the
crucial role of Coulomb friction which induces two main regimes: (i) rare
collisions (RC), with an average drift $\ < \omega \ > \sim v_0^3$, and (ii)
frequent collisions (FC), with $\ < \omega \ > \sim v_0$. We also study the
fluctuations of the angle spanned in a large time interval, $\Delta \theta$,
which in the FC regime is proportional to the work done upon the motor. We
observe that the Fluctuation Relation is satisfied with a slope which weakly
depends on the relative collision frequency.
