Abstract: A gyroscopic traction drive assembly comprises a rotatable frame which carries a rotatable traction input member and a rotatable traction output member. The input and output members frictionally engage a spherical gyroscopic mass at respective points thereon which lie in a common plane which is perpendicular to the axis of rotation of the frame. Rotation of the frame causes the mass to rotate about a first axis passing through its center and perpendicular to the common plane and a second angular velocity is also imparted to the mass about a second axis, due to the frictional contact with the traction input member, which second axis is orthogonal to the first axis and lies in the common plane. These combined motions produce a gyroscopic output torque about a third axis, orthogonal to the first and second axes, which is imparted to the traction output member.