This is the Futaba BLS254 Brushless Heli Rudder Servo.
When using with the GY520 you must make sure you change to
the correct mode in the gyro software.

FEATURES: Designed for 3D helis
Standard size
Equipped with two ball bearings
30% faster response than standard digital servos and five times
longer lasting than servos with brushed motors
Same power consumption as brushed digital servos
INCLUDES: Futaba BLS254 Brushless Heli Rudder Servo with universal connector
(21mm) diameter round horn, 1.8" (45mm) diameter round horn 1.2"
(32mm) diameter 6-point horn, 1.5" (38.8mm) diameter 4-point horn
mounting screws, eyelets and grommets
REQUIRES: Installing in heli, connecting linkage and connecting to receiver
SPECS:    Torque: 53 oz-in (3.8kg/cm) @ 4.8V
Speed: 0.06 sec/60° @ 4.8V
Size: 1.60 x 0.80 x 1.50" (40 x 20 x 36.8mm)
Weight: 1.80 oz (51g)