Linear actuator creates motion in a straight line, in contrast to the circular motion of a conventional electric motor. Used in computers peripherals such as disk drives and printers. Wide variety of application in Robotics. Also used on dampers and valves. Could be  outfitted with outer gear system to produce various speeds or torques. Also could be paired with electronic speed control to vary the speed of the linear shaft movement. Available in 4, 8, 12, 18, 24 volts. Please specify torque, and the shafts length