A drive tower for a circular irrigation system includes an upright frame for supporting a water pipe which extends radially from a central pivot. The frame is supported on wheels power rotated by an electric motor to drive the tower in a circular path around the pivot. To turn the wheels, the motor rotates a power shaft to reciprocate two pawls through alternating power strokes by means of two eccentrics each of which is mounted on the shaft and rotates within one of the pawls. As the pawls are alternately driven through their power strokes, they push against the teeth of a drive gear keyed to a drive shaft which connects to the wheels so that, as the pawls rotate the gear, the wheels are turned to move the tower. The pawls are shaped symmetrically so that either of their opposite ends may fit between the teeth of the gear, and reversible spring means selectively hold the adjacent ends of the pawls against the gear during the power stroke to drive the gear in one direction. By reversing the action of the spring means, the other adjacent ends of the pawls are pressed against the gear so the latter may be driven in the opposite direction. Solenoids controlling the reversal of the spring means enable an operator to reverse the direction of movement of the tower from a remote location.
