I Agree its a foley noise maker, for radio shows. The 6 slats have a tension adjuster at the bottom, that pulls them into the top roller..when the roller is turned, it creates two simultaneos sounds...like " ti-ta-tat"..like a horse gallop, trot, canter, walk, depending on the speed the crank is turned. The canvas thrown over roller could creat a dampened sound for a horse walking on softer surfaces.
It's possible :)