FEETECH Standard Servo FS5103B-FB with Position Feedback

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This version of the FS5103B standard servo from FEETECH is specially modified to provide access to the feedback potentiometer through a fourth (green) wire, allowing you to directly measure the position of the output.

This extra information enables more complex robotics applications, such as determining when the servo has reached its target, detecting when the output is blocked, or implementing your own higher-level closed-loop position control.

Key specs at 6 V: 0.16 sec/60°, 53 oz-in (3.8 kg-cm), 43 g.

  • Horn gear spline - 25 Teeth

FEETECH Standard Servo FS5103B-FB with Position Feedback. The FEETECH Standard Servo FS5103B has a plastic gear train and two ball bearings on the output. FEETECH Standard Servo FS5103B with included hardware (actual hardware might vary). Servo and feedback connectors on the FEETECH servos with position feedback.
FEETECH Standard Servo FS5103B-FB with Position Feedback.

The FS5103B-FB is a specially modified version of FEETECH’s FS5103B standard-size analog servo that provides access to the feedback potentiometer through a fourth (green) wire, which makes it possible to directly measure the output angle. With this extra information, you can determine when the servo has reached its target position (or detect if something is interfering with its ability to get there). This feedback also enables more complex closed-loop control of the servo from your main controller.

Like the FS5103B, the FS5103B-FB works with standard RC servo pulses, providing a running angle of approximately 180° over a servo pulse range of 600 µs to 2400 µs. The feedback voltage varies linearly over this range, and there is approximately a 1:1 correspondence between the feedback in millivolts and the servo position in milliseconds. For example, the feedback voltage will be around 1.5 V when the servo output is at the position corresponding to 1.5 ms.

The servo signal, power, and ground are provided through a 3-wire servo cable that is terminated with a standard  JR-style connector, which is Futaba-compatible. The feedback is accessible through a separate green wire that is terminated like our female premium jumper wires and works with standard 0.1″ male header pins. These cables are approximately 12″ (30 cm) long.

Size 40.8 × 20.1 × 38 mm
Weight: 43g
Digital ?:   N
Speed @ 6V:   0.16 sec/60°
Stall torque @ 6V:   3.8 kg·cm
Speed @ 4.8V:   0.18 sec/60°
Stall torque @ 4.8V:   3 kg·cm
Lead length:   12 in
Hardware included ?:   Y


  • Datasheet for the FEETECH Standard Servo FS5103B (133k pdf)

    Note: while this datasheet lists the 6 V stall torque as 3.2 kg*cm, Feetech has since revised this to 3.8 kg*cm based on more recent measurements (this is also more in line with their listed 4.8 V stall torque of 3.0 kg*cm). (please note that this is the datasheet for the standard FS5103B, so it does not include any information about the special feedback modification).

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