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Receivers (RX)

A receiver is used to receive radio control signals from your transmitter and convert them into signals that the flight controller can understand.

There are 3 basic types of receivers:

  1. Parallel PWM Receivers
  2. PPM Receivers
  3. Serial Receivers

As of 2016 the recommendation for new purchases is a Serial or PPM based receiver. Avoid Parallel PWM recievers (1 wire per channel). This is due to the amount of IO pins parallel PWM based receivers use. Some new FC's do not support parallel PWM.

Parallel PWM Receivers​

8 channel support, 1 channel per input pin. On some platforms using parallel input will disable the use of serial ports and SoftSerial making it hard to use telemetry or GPS features.

PPM Receivers​

PPM is sometimes known as PPM SUM or CPPM.

12 channels via a single input pin, not as accurate or jitter free as methods that use serial communications, but readily available.

These receivers are reported working:

Serial Receivers​

Spektrum​

8 channels via serial currently supported.

These receivers are reported working:

Lemon Rx DSMX Compatible PPM 8-Channel Receiver + Lemon DSMX Compatible Satellite with Failsafe http://www.lemon-rx.com/index.php?route=product/product&product_id=118

S.BUS​

16 channels via serial currently supported. See below how to set up your transmitter.

  • You probably need an inverter between the receiver output and the flight controller. However, some flight controllers have this built in (the main port on CC3D, for example), and doesn't need one.
  • Some OpenLRS receivers produce a non-inverted SBUS signal. It is possible to switch SBUS inversion off using CLI command set sbus_inversion = OFF when using an F3 based flight controller.
  • Softserial ports cannot be used with SBUS because it runs at too high of a bitrate (1Mbps). Refer to the chapter specific to your board to determine which port(s) may be used.
  • You will need to configure the channel mapping in the GUI (Receiver tab) or CLI (map command). Note that channels above 8 are mapped "straight", with no remapping.

These receivers are reported working:

FrSky X4RSB 3/16ch Telemetry Receiver http://www.frsky-rc.com/product/pro.php?pro_id=135

FrSky X8R 8/16ch Telemetry Receiver http://www.frsky-rc.com/product/pro.php?pro_id=105

Futaba R2008SB 2.4GHz S-FHSS http://www.futaba-rc.com/systems/futk8100-8j/

OpenTX S.BUS configuration​

If using OpenTX set the transmitter module to D16 mode and ALSO select CH1-16 on the transmitter before binding to allow reception of all 16 channels.

OpenTX 2.09, which is shipped on some Taranis X9D Plus transmitters, has a bug - issue:1701. The bug prevents use of all 16 channels. Upgrade to the latest OpenTX version to allow correct reception of all 16 channels, without the fix you are limited to 8 channels regardless of the CH1-16/D16 settings.

SRXL (formerly XBUS)​

(Serial Receiver Link Protocol) SRXL is an open data transfer protocol which allows to transport control data from a rc receiver to another device like a flybarless system by only using one single line. This protocol has been established by SRXL.org based on the idea to create a freely available and unified protocol that manufacturers can easily implement to their receivers and devices that process receiver data. The protocol does not describe an exact definition of how the data must be processed. It only describes a framework in which receiver data can be packed. Each manufacturer can have his own ID, which must be attached to the beginning of each data set, so that the device using this data can correctly identify and process the payload of the dataset.

Supported receivers:

Multiplex:​

All receivers with SRXL (also FLEXX receivers)

####Gaupner / SJ HOTT: All receiver with SUMD support

Spektrum:​

AR7700 / AR9020 receiver

JR:​

JR X-BUS Make sure to set your TX to use "MODE B" for XBUS in the TX menus! See here for info on JR's XBUS protocol: http://www.jrpropo.com/english/propo/XBus/ These receivers are reported working:

XG14 14ch DMSS System w/RG731BX XBus Receiver http://www.jramericas.com/233794/JRP00631/

Jeti:​

Receivers with UDI output

XBUS MODE B RJ01​

There exist a remote receiver made for small BNF-models like the Align T-Rex 150 helicopter. The code also supports using the Align DMSS RJ01 receiver directly with the cleanflight software. To use this receiver you must power it with 3V from the hardware, and then connect the serial line as other serial RX receivers. In order for this receiver to work, you need to specify the XBUS_MODE_B_RJ01 for serialrx_provider. Note that you need to set your radio mode for XBUS "MODE B" also for this receiver to work. Receiver name: Align DMSS RJ01 (HER15001)

SUMD​

16 channels via serial currently supported.

These receivers are reported working:

GR-24 receiver HoTT http://www.graupner.de/en/products/33512/product.aspx

Graupner receiver GR-12SH+ HoTT http://www.graupner.de/en/products/870ade17-ace8-427f-943b-657040579906/33565/product.aspx

SUMH​

8 channels via serial currently supported.

SUMH is a legacy Graupner protocol. Graupner have issued a firmware updates for many recivers that lets them use SUMD instead.

IBUS​

10 channels via serial currently supported.

IBUS is the FlySky digital serial protocol and is available with the FS-IA4B, FS-IA6B and FS-IA10 receivers. The Turnigy TGY-IA6B and TGY-IA10 are the same devices with a different label, therefore they also work.

If you are using a 6ch tx such as the FS-I6 or TGY-I6 then you must flash a 10ch firmware on the tx to make use of these extra channels.

These receivers are reported working (all gives 10 channels serial):

Combine flysky ibus telemetry and serial rx on the same FC serial port​

Connect Flysky FS-iA6B receiver like this:

    +---------+
    | FS-iA6B |
    |         |
    | Ser RX  |---|<---\       +------------+
    |         |        |       | FC         |
    | Sensor  |--#==#--*-------| SerialTX   |
    +---------+                +------------+

Use a diode with cathode to receiver serial rx output (for example 1N4148), the anode is connected to the FC serial TX pin, and also via a resistor (10KOhm) to the receiver ibus sensor port.

Note (2018-07-27): In some cases, the value of the series resistor may be too large, and going down to 1K[ohm] may provide a good result.

Enable with cli:

    serial 1 1088 115200 57600 115200 115200
    feature RX_SERIAL
    set serialrx_provider = IBUS
    save

Jeti EX Bus​

It supports 16 channels with a transfer rate of 100Hz. The HS option (High Speed) is currently not supported. The receiver must be configured in the device manager to EX Bus and connected to a free FC serial TX pin. For more information on the wiring and setup see this document.

MultiWii serial protocol (MSP)​

Allows you to use MSP commands as the RC input. Only 8 channel support to maintain compatibility with MSP.

Configuration​

There are 3 features that control receiver mode:

RX_PPM
RX_SERIAL
RX_PARALLEL_PWM
RX_MSP

Only one receiver feature can be enabled at a time.

RX signal-loss detection​

The software has signal loss detection which is always enabled. Signal loss detection is used for safety and failsafe reasons.

The rx_min_usec and rx_max_usec settings helps detect when your RX stops sending any data, enters failsafe mode or when the RX looses signal.

By default, when the signal loss is detected the FC will set pitch/roll/yaw to the value configured for mid_rc. The throttle will be set to the value configured for rx_min_usec or mid_rc if using 3D feature.

Signal loss can be detected when:

  1. no RX data is received (due to radio reception, receiver configuration or cabling issues).
  2. using Serial RX and receiver indicates failsafe condition.
  3. using any of the first 4 stick channels do not have a value in the range specified by rx_min_usec and rx_max_usec.

RX loss configuration​

The rxfail cli command is used to configure per-channel rx-loss behavior. You can use the rxfail command to change this behavior. A flight channel can either be AUTOMATIC or HOLD, an AUX channel can either be SET or HOLD.

  • AUTOMATIC - Flight channels are set to safe values (low throttle, mid position for yaw/pitch/roll).
  • HOLD - Channel holds the last value.
  • SET - Channel is set to a specific configured value.

The default mode is AUTOMATIC for flight channels and HOLD for AUX channels.

The rxfail command can be used in conjunction with mode ranges to trigger various actions.

The rxfail command takes 2 or 3 arguments.

  • Index of channel (See below)
  • Mode ('a' = AUTOMATIC, 'h' = HOLD, 's' = SET)
  • A value to use when in SET mode.

Channels are always specified in the same order, regardless of your channel mapping.

  • Roll is 0
  • Pitch is 1
  • Yaw is 2
  • Throttle is 3.
  • Aux channels are 4 onwards.

Examples:

To make Throttle channel have an automatic value when RX loss is detected:

rxfail 3 a

To make AUX4 have a value of 2000 when RX loss is detected:

rxfail 7 s 2000

To make AUX8 hold it's value when RX loss is detected:

rxfail 11 h

WARNING: Always make sure you test the behavior is as expected after configuring rxfail settings!

rx_min_usec​

The lowest channel value considered valid. e.g. PWM/PPM pulse length

rx_max_usec​

The highest channel value considered valid. e.g. PWM/PPM pulse length

Serial RX​

See the Serial chapter for some some RX configuration examples.

To setup spectrum on the Naze32 or clones in the GUI:

  1. Start on the "Ports" tab make sure that UART2 has serial RX. If not set the checkbox, save and reboot.
  2. Move to the "Configuration" page and in the upper lefthand corner choose Serial RX as the receiver type.
  3. Below that choose the type of serial receiver that you are using. Save and reboot.

Using CLI: For Serial RX enable RX_SERIAL and set the serialrx_provider CLI setting as follows.

Serial RX ProviderValue
SPEKTRUM10240
SPEKTRUM20481
SBUS2
SUMD3
SUMH4
XBUS_MODE_B5
XBUS_MODE_B_RJ016
IBUS7
JETIEXBUS8

PPM/PWM input filtering.​

Hardware input filtering can be enabled if you are experiencing interference on the signal sent via your PWM/PPM RX.

Use the input_filtering_mode CLI setting to select a mode.

ValueMeaning
OFFDisabled
ONEnabled

Receiver configuration.​

FrSky D4R-II​

Set the RX for 'No Pulses'. Turn OFF TX and RX, Turn ON RX. Press and release F/S button on RX. Turn off RX.

Graupner GR-24 PWM​

Set failsafe on the throttle channel in the receiver settings (via transmitter menu) to a value below rx_min_usec using channel mode FAILSAFE. This is the preferred way, since this is much faster detected by the FC then a channel that sends no pulses (OFF).

NOTE: One or more control channels may be set to OFF to signal a failsafe condition to the FC, all other channels must be set to either HOLD or OFF. Do NOT USE the mode indicated with FAILSAFE instead, as this combination is NOT handled correctly by the FC.

Receiver Channel Range Configuration.​

The channels defined in CleanFlight are as follows:

Channel numberChannel name
0Roll
1Pitch
2Yaw
3Throttle

If you have a transmitter/receiver, that output a non-standard pulse range (i.e. 1070-1930 as some Spektrum receivers) you could use rx channel range configuration to map actual range of your transmitter to 1000-2000 as expected by Cleanflight.

The low and high value of a channel range are often referred to as 'End-points'. e.g. 'End-point adjustments / EPA'.

All attempts should be made to configure your transmitter/receiver to use the range 1000-2000 before using this feature as you will have less precise control if it is used.

To do this you should figure out what range your transmitter outputs and use these values for rx range configuration. You can do this in a few simple steps:

If you have used rc range configuration previously you should reset it to prevent it from altering rc input. Do so by entering the following command in CLI:

rxrange reset
save

Now reboot your FC, connect the configurator, go to the Receiver tab move sticks on your transmitter and note min and max values of first 4 channels. Take caution as you can accidentally arm your craft. Best way is to move one channel at a time.

Go to CLI and set the min and max values with the following command:

rxrange <channel_number> <min> <max>

For example, if you have the range 1070-1930 for the first channel you should use rxrange 0 1070 1930 in the CLI. Be sure to enter the save command to save the settings.

After configuring channel ranges use the sub-trim on your transmitter to set the middle point of pitch, roll, yaw and throttle.

You can also use rxrange to reverse the direction of an input channel, e.g. rxrange 0 2000 1000.

Disabling the OpenTx/EdgeTx ADC Filter​

OpenTx and EdgeTx both enable an ADC filter by default. Betaflight users should turn this off.

The ADC filter converts what would otherwise be smooth changes in channel values into a series of steps, where each step is about 1% of the full stick travel. It is intended to reduce 'chatter' when the Rx is connected to a *servo, so that the servo only changes position when a meaningful change has occurred. It is not intended for use with flight controllers.

When the ADC Filter is active, Betaflight does not receive the most recent position of the gimbal with each new RC packet. Instead, the Rx repeatedly provides the same data, until a moving-averaged smoothed estimate of gimbal position has increased by about 1% of full stick resolution.

Betaflight needs a non-delayed, smooth and continuous representation of the stick travel to give the PID system a smooth target setpoint value. Our RC Smoothing is based on the assumption that every packet is unique and that each is a new representation of the most recent position of the gimbal. Feedforward is calculated from the packet-to-packet position difference, and absolutely relies on smooth and regular updates in measured gimbal position.

When active with Betaflight firmware, the ADC filter causes:

  • delay (from the moving averaging)
  • sustained transient impacts
  • steps in setpoint
  • spikes and noise in feedforward, with reduced feedforward precision
  • spikes in motor control signals that may cause noticeable jerking in HD video

This is why, whenever an OpenTx or EdgeTx user is using Betaflight, the OpenTx/EdgeTx ADC Filter MUST be disabled, for accurate smooth flight control.

The user only has to find the ADC Filter checkbox in the Hardware tab of the Global Settings for their radio, and ensure it is un-checked. For example, with the FrSky Taranis X9D+ pre 2019 model:

  • Turn on your radio.
  • Hold Menu to access Global Settings.
  • Click the Page button 5 times to go to page 6 (HARDWARE).
  • Scroll down and select ADC filter.
  • Click Enter to disable the ADC filter as it's enabled by default.
  • Click Exit (twice) to return to the startup screen.