The Servo Failsafe Unit is a device that is inserted between the receiver and a servo in order to check the signal's validity to the servo.

The valid signals are passed unaltered and the servo operates normally
If an invalid signal arrives (interference or total loss of signal from the transmitter) then the SFU1 directs the servo to a predefined ,by you, failsafe position which is memorized.
This failsafe position is defined simply by moving the stick that commands the servo to the desirable position and then pressing the on board microswitch for a second.The failsafe position can be altered as many times you want in order to trim the servo's position accurately.After that each time the receiver's signal is invalid the servo reverts to the failsafe position and stays there until a valid signal arrives again.The servo's position is stored in SFU1's memory and is been remembered until you decide to alter it.

The SFU1 is intended to work with 4,8V receivers with positive going pulses 0,9 ms - 2,2ms and 20 ms frame which is the most popular format that can be found in the vast majority of Radio Control Systems used by RC modellers.
It also checks the battery's voltage and if the voltage drops below 4,55V it initiates a special warning programm by moving the servo to the failsafe position every 5 seconds.
If the check for low battery voltage is not desirable it can be disabled.
To disable the battery low programm just turn ON the receiver switch while pressing the on board microswitch for a second or so and thats all.You can restore back the battery low function at any time just by doing the same thing.
There is no limitation on how many SFU1's can be used on a Radio Controlled Model.

EXAMPLE
Install a Servo Failsafe Unit in between the receiver and the throttle servo on your model.Turn on both transmitter and receiver.Move the throttle stick to the lowest setting (iddling or stop engine position for exmple) and then press the SFU1's on board microswitch to memorize this position.That is all
Then in case your receiver looses the transmitter's signal your engine will either stop or iddle avoiding or minimizing damages.
If the battery low function is operative then if the receiver's battery falls below 4,55V the SFU1 commands the servo to the failsafe position for 1 second every 5 seconds giving you warning that it is time to stop.

Boat modellers use it to set the steering servo for making a medium radius turn so the boat does not get away and/or use a separate SFU1 to throttle down the engine.
Airplane and car modellers usually connect it to the throttle servo.

Dimensions 30 X 20 X 8 mm
Weight 5gr
Operating votage 3,3V - 6V DC
Curent drain 1mA (SFU1 with no servo attached)