The FS0403-FB is a specially modified version of FEETECH’s FS0403 sub-micro 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 FS0403, the FS0403-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 180° over a pulse range of 650 µs to 2500 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 6″ (15 cm) long.
Servo and feedback connectors on the FEETECH servos with position feedback.
For more information about this servo, see the FS0403 datasheet (97k pdf) (please note that this is the datasheet for the standard FS0403 sub-micro servo, so it does not include any information about the special feedback modification).
An example of hardware included with the FEETECH FS0403 sub-micro servo. Actual hardware might vary.
Note that, as with most hobby servos, stalling or back-driving this servo can damage it.
