A rotary blasthole drilling apparatus comprises a rotary blasthole drill and a drill automation control system. The apparatus includes a pull-down motor and a drill motor. The pull-down motor is driven by a pump to provide a pull-down force to a drill string, and the drill motor is used to provide rotary...http://www.google.es/patents/US5465798?utm_source=gb-gplus-sharePatente US5465798 - Drill automation control system
