Evidently, rocking a cradle is hard work because another inventor devised his own motor-driven cradle, which could run for two hours unattended. Like the Vanderburgh's hammock, Luther P. Jones' cradle used a clock mechanism to keep it going. As you can see from the illustration, though, Jones' device could hold quite the load. The cradle hung on chains fastened to a metal frame, which would also keep the clock machine in place. To operate it, simply wind up the spring and watch as the motor turns a wheel. The motion would cause the bar holding the chain to swing, which would in turn rock the baby to sleep. The gears would also provide entertainment for the baby in case it woke up alone.
Read the full story in "The Motor that Rocks the Cradle"