Merge pull request #11024 from ctzsnooze/update-Rx.md-note-about-ADC-filter
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docs/Rx.md
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docs/Rx.md
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@ -362,3 +362,33 @@ After configuring channel ranges use the sub-trim on your transmitter to set the
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You can also use rxrange to reverse the direction of an input channel, e.g. `rxrange 0 2000 1000`.
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## Disabling the OpenTx/EdgeTx ADC Filter
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OpenTx and EdgeTx both enable an `ADC filter` by default. Betaflight users should turn this off.
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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.
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When the `ADC Filter` is active, Betaflight does not receive the most recent position of the gimabl 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.
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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.
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When active with Betaflight firmware, the `ADC filter` causes:
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- delay (from the moving averaging)
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- sustained transient impacts
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- steps in setpoint
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- spikes and noise in feedforward, with reduced feedforward precision
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- spikes in motor control signals that may cause noticeable jerking in HD video
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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.
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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:
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* Turn on your radio.
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* Hold Menu to access Global Settings.
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* Click the Page button 5 times to go to page 6 (HARDWARE).
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* Scroll down and select ADC filter.
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* Click Enter to disable the ADC filter as it's enabled by default.
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* Click Exit (twice) to return to the startup screen.
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