FEETECH FS90-FB Micro Servo with Position Feedback
This version of the FS90 micro 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: 0.10 sec/60°, 21 oz-in (1.5 kg-cm), 13 g.
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FEETECH FS90 Micro Servo with a LEGO Minifigure as a size reference.
The FS90-FB is a specially modified version of FEETECH’s FS90 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 FS90, the FS90-FB works with standard RC servo pulses, providing a running angle of approximately 120° over a servo pulse range of 900 µs to 2100 µs. 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. 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 an extra-long 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 15″ (38 cm) long (which is almost twice as long as the cables on the standard FS90).
Servo and feedback connectors on the FEETECH servos with position feedback.
For more information about this servo, see the FS90 datasheet (69k pdf) (please note that this is the datasheet for the standard FS90, so it does not include any information about the special feedback modification, and the specified cable length does not apply).
The following picture shows an example of the hardware that might be included (actual hardware could vary):
Note that as with most hobby servos, stalling or back-driving this servo can damage it.
FS90 vs FS90R
Two versions of this servo are available. This product is the FS90, which offers closed-loop position control over a limited range. Alternatively, the FS90R is specifically designed to be a continuous-rotation micro servo that offers open-loop speed control. The FS90 and FS90R have identical dimensions and use the same motor, so the FS90 will also work with our 60×8mm wheel for the FEETECH FS90R.