The FT1117M-FB is a specially modified version of FEETECH’s FT1117M miniature-sized 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.
The FT1117M-FB is a miniature-sized servo from FEETECH with the same output spline as standard servos, making it compatible with standard-size servo horns. The pinion gear is plastic, but the rest of the gear train consists of all metal gears, allowing this servo to deliver the kind of speed and torque typically associated with larger servos.
Like the FT1117M, the FT1117M-FB works with standard RC servo pulses, providing an operating angle of approximately 120° over a servo pulse range of 900 µs to 2100 µs. The feedback voltage varies linearly over this range by a couple of volts. As with most servos, the pulse range can be expanded to achieve an expanded operating angle, but the limits of this are not specified by FEETECH. (In our tests, we were able to get an expanded range of approximately 165° over a pulse range of 550 µs to 2400 µs, but as this is not part of FEETECH’s official specifications, it is possible different units will behave differently in this regard.)
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 7″ (18 cm) long.
Servo and feedback connectors on the FEETECH servos with position feedback.
For more information about this servo, see the FT1117M datasheet (125k pdf) (please note that this is the datasheet for the standard FT1117M, so it does not include any information about the special feedback modification).
FEETECH Mini Servo FT1117M with included hardware (actual hardware might vary).
Note that, as with most hobby servos, stalling or back-driving this servo can damage it.
Comparison to the Power HD 1711MG servo
The FT1117M is a lower-cost alternative to the 1711MG from Power HD, which has nearly identical dimensions and similar performance. The two servos should be generally interchangeable for most applications. The picture below shows both the FT1117M and the 1711MG side by side:
