It’s important to setup failsafe properly on your mini quad for maximum safety and preventing fly-away. In this tutorial I will explain what failsafe is, and how to set it up in Betaflight as well as on your Taranis TX radio transmitter and receiver.
Table of Content
- What is Failsafe
- Setup Failsafe in Taranis
- Setup Failsafe on Frsky RX
- Setup Failsafe in Betaflight
- Test Failsafe
What’s a Failsafe?
A failsafe is what the RC model does when connection or signal is lost between the radio transmitter and receiver. The common causes of a failsafe are:
- radio signal is out of range when you fly too far away
- signal is blocked by obstacles
- TX or RX is switched off, lost power or malfunctioning
- receiver is accidentally disconnected from the flight controller
You can program failsafe to do whatever you want when you lose radio signal. The goal is for safety and minimizing damage to the surrounding, and even saving your model when you lose signal.
Common failsafe actions are holding the last stick position, or keep throttle low for slow descent. But it’s generally advised to cut throttle as soon as failsafe happens. This should disable or stop all the motors, and your quad should just drop vertically to the ground.
A racing drone with uncontrolled spinning propellers can be extremely dangerous. Therefore it’s better to crash your quadcopter and repair it later, rather than hurting someone badly.
Another possibility without setting up failsafe properly, is that your aircraft might just continue flying when signal is lost, until it disappeared off the horizon and never to be found again – what is commonly known as a “fly-away”
When you lose video in the FPV goggles, you can also just disarm or switch off transmitter to “emergency-land” your mini quad. This can prevent it from wandering around further, making the search harder.
How To Setup Failsafe?
Many transmitters and receivers support failsafe. If you are using a cheap radio, it might not support this feature, but perhaps you can still get it setup in the flight controller (e.g. in Betafligiht).
You should set up failsafe in at least one of these places, and it certainly doesn’t hurt to setup all of them to have extra layers of safety.
Most importantly, make sure you test failsafe thoroughly before taking off.
Further Reading: My Tools, Gears and Quads
Setup Failsafe in the Radio (Taranis)
The Frsky Taranis is one of the few radios that you can setup failsafe directly there, the failsafe settings will then be passed on to the receiver. If you use other radios, no big deal, just set it up in the flight controller or receiver.
So here is how to setup failsafe in the Taranis.
Go to the Setup Page on your Taranis, scroll down to “Internal RF Module”.
I recommend “No Pulses”. You also get the following options and here is what they do:
- Not Set, this is the default; When failsafe happens the quad will just fall to the ground (same as No Pulses as far as I can tell, but you sometimes get an annoying prompt at power up saying you haven’t setup failsafe)
- Hold, it will hold the last stick/switches positions; Maybe useful for planes and wings, but not a good idea for multirotors especially racing or acro quads as you might be doing a flip when FS happens and the quad will keep rolling until it crashes into the ground, or it might simply fly away…
- Custom, it might be useful if you use angle mode (self level), you can set a lower throttle level and the quad will slowly descent. This might be useful in case you can regain control before it hits the ground; But you don’t always know what would be below the quad, landing a quad without control with spinning props can be dangerous
- No Pulses, when failsafe is triggered, the quad will just stop and drop to the ground, in my opinion the ideal failsafe option for mini quad
- Receiver, failsafe on the TX will depend on the FS setting on the RX
Setup Failsafe on the Receiver
You should setup failsafe on the receiver if you are not using a flight controller, such as RC plane and flying wing.
Note: setting up failsafe on the receivers that are using analog protocols such as PWM and PPM, might actually prevent your flight controller from knowing failsafe has happened, and so it wouldn’t switch to failsafe mode. That’s because the receiver is still sending valid signals, and not the failsafe flag.
However, this is generally not the case for serial protocols such as SBUS, because it always sends the failsafe flag. So don’t worry if you are using SBUS, you can set it up on your receiver and your flight controller, and failsafe should still work. But don’t just take my words for it, please test your setup thoroughly before flying.
All radio receivers have failsafe, and most allow you to configure it in some way.
Spektrum receivers’ failsafe is setup during binding, they remember the stick (throttle) positions when they are bound together. Rebinding can reset failsafe.
For most Frsky receivers, there is a dedicated failsafe button (F/S or FS button), when pressed it remembers the stick position. To cut throttle at failsafe, make sure the throttle stick is at its lowest position when you press the button.
If failsafe is not set or enabled, the default behaviour is to hold last stick position when the signal is lost, which you should avoid.
Check out this list of Frsky receivers for mini quads.
It’s explained pretty well in the Frsky receiver manual how to do this step by step:
- Bind the receiver first and turn on both the transmitter and receiver;
- Move the controls to the desired failsafe position for all channels;
- Held down the F/S button of the receiver (for a second). The GREEN LED of the receiver will
flash twice, indicating the failsafe position has been set in the receiver.
- To disable/reset the failsafe function, re-bind the receiver.
Failsafe Configuration in Betaflight
If you have failsafe setup in your TX and/or RX, the defaults Failsafe configuration in Betaflight is just fine. All that matters is your motors stop spinning when you turn off the radio.
But if you can’t setup failsafe in neither your TX or RX, here is how I normally setup failsafe in Betaflight.
- Enable Expert mode, and a new tab “Failsafe” will appear
- Enable Failsafe Stage 2
- Check “Drop”, I don’t recommend using “Land” unless you are experienced enough and know what you are doing
- Only change the failsafe delay if you know what you are doing, otherwise leave it at default (e.g. you might want to increase delay if you fly over water and want to buy some time in case the radio link can recover by moving the TX around)
What are Stage 1 and Stage 2 Failsafe?
Stage 1 Failsafe is activated when the receiver reports failsafe to the flight controller.
If the failsafe lasts longer than the time you’ve specified in Betaflight, it will go into Stage 2. This is set to a second by default (guard time). Note that you can also activate Stage 2 Failsafe directly using a switch (setup in modes tab).
So do I need to change anything in Stage 1? It depends.
If the failsafe you are experiencing is just a temporary signal dropout, Stage 1 might give you a chance to regain control and recover without crashing. But if this happens, please land and investigate the cause of the signal issue.
Basically there are two options you should change for each channel, Auto or Hold.
If you normally fly in acro mode, then it’s best to set “Auto” to roll, pitch, and yaw channels. It basically stops any rotation in those axis when failsafe happens. With “Hold”, your quad will continue to spin which is really not a good idea. For Angle mode, it really doesn’t matter as the quad would be flying in a controlled fashion anyway, and Stage 1 only lasts less than a second.
When it comes to the throttle channel, it depends on your preference.
“Auto” will basically stop the motors, and your quad will just drop to the ground. “Hold” will, well, hold the throttle, which might make it easier for you to recover if signal is back. If not your quad will continue to travel for 1 extra second which might make the impact worse.
Once you have setup failsafe, make sure to test it to work exactly the way you want it to.
REMOVE propellers, arm the quad and give it a little throttle so the motors start spinning. Now turn your radio off to see what happens.
Advance Failsafe: Rescue Mode
Betaflight introduced a new failsafe option, Rescue mode.
Not exactly the same, but similar to Return to Home, the quad would fly back towards where it started with the help of a GPS module to restore signal link.
Here is the tutorial how to set up GPS rescue mode in Betaflight.