RadioMaster R81 Receiver User Manual

Product Features and Specifications

The RadioMaster R81 is an 8-channel receiver designed for radio control systems.

Specifications:

Channels:

8

Frequency Range:

2400-2483.5MHz

Power Input Range:

4.5-6V

Signal Format:

D8

Output Format:

SBUS

Support Return:

Supports RSSI return

Control Distance:

More than 1km

Antenna Length:

Approximately 6cm

Size:

17x11mm

Weight:

2grams

A diagram shows the receiver's connection pins: S.BUS, DC4.5-6V (power input), and GND (ground).

Bind Method

Follow these steps to bind the R81 receiver to your remote control:

1. Press and hold the BIND button on the receiver, then connect power. After approximately 3 seconds, the receiver LED will turn solid RED, indicating it is in bind mode.
2. On your remote control, select the D8 protocol within the multi-protocol menu and press the [BIND] option. The receiver's red LED will flash, signifying successful binding.
3. Exit bind mode on your remote control, disconnect power to the receiver, and then power it on again. The LED should now be solid RED, confirming the bind is complete. If not, repeat steps 1 and 2.

[Note] This receiver does not support Frsky transmitters; it is compatible only with MPM (Multi-Protocol Module) radios.

Fail-safe Protection

Fail-safe protection ensures the model maintains a safe state in case of signal loss.

1. Within 10 seconds of powering on the receiver, press the BIND button once. This action saves the current channel values from the remote control as the fail-safe values.
2. After 10 seconds from receiver power-on, the BIND button function will be disabled. This prevents accidental changes to the fail-safe settings while preparing the model for flight.

RSSI Output

The R81 receiver provides RSSI (Received Signal Strength Indicator) output.

This receiver offers a total of 9 SBUS channels: 8 control channels and 1 RSSI output channel. Channels 1-8 are controlled by the remote controller. The 9th channel transmits the signal strength RSSI value from the receiver. This value can be read by flight controllers and sent to an On-Screen Display (OSD) device to show signal strength in the FPV video feed.

Frequency Fine-Tuning

[Note] For optimal remote control range and stability, it is essential to perform frequency fine-tuning for D8 and D16 compatible receivers before initial use. This process corrects frequency errors between the transmitter and receiver.

Follow these steps:

1. Gradually decrease the value of the 'RF Freq. fine tune' setting until the receiver loses signal. Record this value (TUNE_MIN, typically a negative number).
2. Gradually increase the 'RF Freq. fine tune' value until the receiver loses signal again. Record this value (TUNE_MAX, typically a positive number).
3. Calculate the midpoint value using the formula: (TUNE_MIN + TUNE_MAX) / 2 = TUNE_MEDIAN.
4. Enter the calculated TUNE_MEDIAN value into the 'RF Freq. fine tune' setting.

Example Calculation:

If the signal is lost at -73 (TUNE_MIN) and +35 (TUNE_MAX), the median is calculated as:

RF Freq. fine tune = (-73 + 35) / 2

RF Freq. fine tune = (-38) / 2

RF Freq. fine tune = -19

Once the correct Fine Tuning value is determined, it can be used for all models utilizing the same protocol.

A screenshot of the 'MODEL SETUP' menu displays configuration options including Channel Range, Receiver binding, RF Frequency Fine Tune, Bind on channel, Disable Telemetry, Low power mode, Failsafe mode, External RF, and Mode.

For more information, visit: https://www.multi-module.org/using-the-module/frequency-tuning