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OpenTX - Application Note 27

X4R Receiver Set Up


Set up an X4R receiver.



The features of the X4R include the following.

   4 channels via individual sockets.

   Smart port used to connect telemetry sensors.

   Status LEDs, red and green.

   F/S (Fail Safe) bushbutton.

   External analog telemetry port (AD2)

Status LEDS

The status of the X4R is indicated by the green and red LEDS as described in this table.


Green LED











Signal Lost

Flash Twice


Failsafe Set


ACCST is FRSky’s Advanced Continuous Channel Shifting Technology. It is the system of communication used between the Taranis and the receiver. The 2.4GHz channel frequency is automatically shifted hundreds of times a second without signal conflicts or interruptions.

Mounting the X4R Receiver in the Aircraft

Mount the receiver as far away from sources of electrical noise (motor, ESC, etc.) as possible. Mount the two antennae perpendicular to each other. Preferably, mount one antenna vertically.

Set Up in the Taranis Radio

In the Model Setup screen, under Internal RF, set the parameters as follows.







16 channel full duplex telemetry.

Channel Range


Assign receiver channel numbers 1 to 8.

Receiver No.

nn [Bind]   [Range]

nn is the number of this model (01 to 60).

[Bind] is used to bind the receiver to the radio.

[Range] is used for checking the receiver range under low power.

Failsafe mode

Hold, or

Custom, or

No Pulses, or


Choose ‘Hold’, ‘Custom’ or ‘No Pulses’ to set the mode in the Taranis radio. Refer here for details.

Choose ‘Receiver’ to set the mode in the receiver.

Refer here for details.


1. On the X4R receiver, press the F/S switch while applying power. The red and green LEDS are on.

2. On the Taranis in the Model Set Up screen under the ‘Internal RF’ heading, use the ‘-‘ and ‘+’ keys to select the ‘[Bind]’ parameter. Press ENT to bind the Taranis model to the receiver. The Taranis beeps and the [BIND] text flashes while in binding mode.

3. After about one second, the receiver red LED flashes. This indicates that binding has been completed. On the Taranis, press EXIT to exit the bind mode.

4. Disconnect power to the receiver.

5. Reconnect power and confirm that the receiver is bound. The green LED is on constantly for normal operation. The red LED flashes slowly if the receiver is not receiving signal.

Failsafe Mode – Set byTaranis

There are three ways to set the channel operation when signal from the transmitter is lost. They are to hold the last position, set to a specified state or set no channel pulses. This is done in the Model Setup screen, under ‘Internal RF’, ‘Failsafe mode’.


If ‘Hold’ is selected, when the receiver loses signal, each channel output holds the last position.


If ‘Custom’ is selected, when the receiver loses signal, each channel is set to the values specified here. Select [Set] and value bars are displayed for each channel. The default value for every channel is zero (centre of range). Select each bar and use the ‘+’ and ‘-‘ buttons to set the failsafe values. Note that the throttle must be set to -100 for throttle to be off.

No Pulses

If ‘No Pulses’ is selected, when the receiver loses signal, pulses from each channel are off.


If ‘Receiver’ is selected, the failsafe mode is set by the receiver. Refer to the next section to set the failsafe mode on the receiver.

Failsafe Mode – Set by Receiver

To set the failsafe mode on the receiver, first in the Taranis radio on the Model Setup screen, under Internal ‘RF’, set the ‘Failsafe mode’ to ‘Receiver. This must be done to enable the failsafe mode to be set in the receiver.

Hold Last Position

Procedure to set failsafe settings to hold last position on signal loss.

1. Re-bind the receiver. The default failsafe setting after binding is to hold each channel at the last position when the signal is lost.

Set Specific State

Procedure to set the failsafe settings to a specified state on signal loss.

1. Bind the receiver to the transmitter first. Turn on both the transmitter and the receiver.

2. Move all the controls to the desired signal loss positions. (eg. Aileron, elevator and rudder centred, throttle off.)

3. Briefly press the F/S button on the receiver. The green LED flashes off twice then returns to constantly on. This completes the failsafe setting procedure.

Set No Pulse Output

Procedure to set failsafe settings to no pulses on signal loss.

1. With the transmitter power off, turn on the receiver. The red LED slowly flashes.

2. Briefly press the F/S button on the receiver. The green LED flashes twice. The red LED continues to flash slowly. This completes the failsafe setting procedure.

Range Check

1. Place the X4R receiver at least 60cm above a non-metallic surface.

2. On the Taranis, in the Model Set Up screen under the ‘Internal RF’ heading, use the ‘-‘ and ‘+’ keys to select the ‘[Range] parameter. Press ENT and the receiver’s RSSI value is displayed.

3. Walk away from the model, checking that all controls operate correctly at least 30m away. The RSSI low alarm is announced if the RSSI value falls below the RSSI Low Alarm value. Press ENT or EXIT to end the range check.

Standard Telemetry

The X4R continuously transmits two standard telemetry data values to the transmitter. These values are AD1 (analog input 1) which is connected to the X4R power supply, and RSSI (Received Signal Strength Indication). When the Taranis loses telemetry reception, a system alarm announces ‘Telemetry Lost’.

AD2 (Analog Input 2)

The AD2 analog input can be connected to an external analog signal like a battery voltage sensor. For the voltage to be measured correctly, the range has to set on the Telemetry (Set Up) screen under the ‘A2 channel’ heading. Set the values as follows.


A2 channel


The current voltage is displayed here.



Set the range here.



  Low Alarm


  Critical Alarm


RSSI (Received Signal Strength Indication)

The RSSI value also appears by default on one of the Taranis standard telemetry screens. It can be used as a source in an Inputs line, or as a variable in a logical switch. Its value can also be announced by the ‘Play Value’ special function.

A low alarm is announced when the RSSI value drops to the Low Alarm parameter. A critical alarm is announced when the RSSI value drops to the Critical Alarm parameter. The Low and Critical Alarm parameters are set on the Telemetry Screen under the RSSI heading. The alarm parameters can be set differently for each model. Use the default values for normal operation.

Data Logging

When data logging is turned on in the Taranis and a logging file is created, all telemetry values are included in the logging file. Refer to Application Note 8 – GPS Sensor for information about turning logging on and displaying the logged data.

More Telemetry – AD2 and Smart Port

There is a 4 pin socket on the side of the X4R which allows connection to the Smart Port and to an analog input AD2. A 4 pin plug with 4 flying leads is supplied with the X4R.


Smart Port Lead

The following photo shows a Smart Port lead made up to connect from the 4 pin socket to a Smart Port compatible JST plug (same as a servo lead plug). Note the twist in the leads to increase electromagnetic noise immunity. In this example, the AD2 input is not connected and its wire end should be insulated to prevent it touching anything with a voltage.



Smart Port compatible sensors can be connected to the receiver Smart Port. Smart Port sensors can be ‘daisy chained’ together. Their data is automatically added to the telemetry transmitted by the X4R to the Taranis radio

Analog Input AD2 Lead

The flying lead of the analog input AD2 can be connected to a voltage divider type battery voltage sensor without requiring the ‘+’ or ‘-‘ pins of the 4 pin connector. The 0V reference for the analog input is provided with the 5V BEC power supply to the X4R. Refer to Application Note 18 for a voltage divider type voltage sensor


Phantom Divide


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