A rotary actuator comprising: a first housing defining a first arcuate chamber comprising a first cavity, a first fluid port in fluid communication with the first cavity, and an open end, wherein the first housing is formed from a single piece of material; a rotor assembly rotatably journaled in said first housing and comprising a rotary output shaft and a first rotor arm extending radially outward from the rotary output shaft; and an arcuate-shaped first piston disposed in said first housing for reciprocal movement in the first arcuate chamber through the open end, wherein a first seal provided about an interior surface of the first arcuate chamber at the open end, the first cavity, and the first piston define a first pressure chamber, and a first portion of the first piston contacts the first rotor arm, wherein application of pressurized fluid to the first pressure chamber urges the first piston partially outward from the first pressure chamber to urge rotation of the rotary output shaft in a first direction, and rotation of the rotary output shaft in a second direction opposite that of the first direction urges the first piston partially into the first pressure chamber to urge pressurized fluid out the first fluid port, wherein the arcuate-shaped first piston is inserted through the open end, and the first seal contacts the interior surface of the first pressure chamber and a substantially smooth surface of the piston end (252, 2752) to form a substantially pressure-sealed region within the first pressure chamber, wherein the first housing further defines a second arcuate chamber comprising a second cavity, and a second fluid port in fluid communication with the second cavity; the rotor assembly further comprises a second rotor arm; the rotary actuator further comprising an arcuate-shaped second piston disposed in said first housing for reciprocal movement in the second arcuate chamber, wherein a second seal, the second cavity, and the second piston define a second pressure chamber, and a first portion of the second piston contacts the second rotor arm, wherein the second piston is oriented in the opposite rotational direction as the first piston. a first housing defining a first arcuate chamber comprising a first cavity, a first fluid port in fluid communication with the first cavity, and an open end, wherein the first housing is formed from a single piece of material; a rotor assembly rotatably journaled in said first housing and comprising a rotary output shaft and a first rotor arm extending radially outward from the rotary output shaft; and an arcuate-shaped first piston disposed in said first housing for reciprocal movement in the first arcuate chamber through the open end, wherein a first seal provided about an interior surface of the first arcuate chamber at the open end, the first cavity, and the first piston define a first pressure chamber, and a first portion of the first piston contacts the first rotor arm, wherein application of pressurized fluid to the first pressure chamber urges the first piston partially outward from the first pressure chamber to urge rotation of the rotary output shaft in a first direction, and rotation of the rotary output shaft in a second direction opposite that of the first direction urges the first piston partially into the first pressure chamber to urge pressurized fluid out the first fluid port, wherein the arcuate-shaped first piston is inserted through the open end, and the first seal contacts the interior surface of the first pressure chamber and a substantially smooth surface of the piston end (252, 2752) to form a substantially pressure-sealed region within the first pressure chamber, wherein the first housing further defines a second arcuate chamber comprising a second cavity, and a second fluid port in fluid communication with the second cavity; the rotor assembly further comprises a second rotor arm; the rotary actuator further comprising an arcuate-shaped second piston disposed in said first housing for reciprocal movement in the second arcuate chamber, wherein a second seal, the second cavity, and the second piston define a second pressure chamber, and a first portion of the second piston contacts the second rotor arm, wherein the second piston is oriented in the opposite rotational direction as the first piston.