Abstract: A speed differential device for achieving selected rotational speed differentials between a drive element and a driven element and comprising a main shaft having a pair of spaced rotational members journalled thereon in spaced relationship, an auxiliary shaft extending transversely with respect to the main shaft and having a pair of rotational elements secured to the outer ends thereof on the opposite sides of the main shaft, the auxiliary shaft being integrated with the main shaft whereby the axis of rotation of the auxiliary shaft is the longitudinal axis of the main shaft, one of the rotational members of the main shaft being in driving engagement with one of the rotational members of the auxiliary shaft for transmitting rotation therebetween, and the other rotational member of the auxiliary shaft being in driving engagement with the other of the rotational elements of the main shaft for transmitting rotation therebetween, the driving size ratio between the engaged rotational elements being selected whereb