Radio Failsafe

What is Failsafe

Whilst the failsafe system has its benefits it does necessarily not mean that you will get your aircraft back in one piece which to some the meaning of failsafe would imply, however it seems to be an alternative to not having any safety features at all.

It is used to pre determine what happens to your servos / speed controller when there is;

Loss of signal from the transmitter to the receiver
Low battery on the receiver
Interference of the radio signal

What can it do for why would I bother?

Sometimes things go wrong. We have all heard of the term “brownout” right? But I have also seen transmitter batteries go flat and in one instance I saw one fall out!

I would prefer to have the throttle go low, and my control surfaces return to a specific position or hold if the signal is lost with the decision of predefined position or hold changes based on what I and flying.  But I have heard from others that they set to quarter to mid throttle with some up elevator because in their experiences 2.4GHz signal loss has occurred on take-off particularly on wet ground, but has recovered.

With modern radios today, then there are generally a couple ways to set it up. With some radios it’s all or none, and others you can set individual channels differently.

There is “Hold” and “Failsafe”

“Hold” means keep the servo where you last had it.  E.g. If you have full up elevator, then it will stay full up.

“Failsafe” means put the servos in a predefined location. E.g. Throttle to idle or ailerons to neutral.

Not setting it varies.  On some systems the servos won’t hold the position, but just be at mercy of the control surfaces they are connect to. Meaning they may stay in position or they may not.

Now there are advantages and disadvantages to both modes, and the idea of this writing is to get YOU thinking so YOU can make the best decision for yourself, but let me paint a couple pictures.

You are flying flat and level at ¾ throttle when you lose signal. 

Failsafe set to so that the aircraft does a slow flat circuit with servos set for a controlled slow descent with throttle to just above idle. until it arrives back to the ground. (of course you would need nil wind with a perfect setup and an active imagination thinking this actually possible), but still….

Hold set, then it will continue its path until the fuel runs out.

You are flying inverted but level at ¾ throttle when you lose signal. 

Failsafe set to all controls to neutral and throttle to just above idle, then it will point itself to the ground at a more aggressive angle due to the neutral elevator. (assuming you need to keep a little back stick for level inverted)

Hold set, then it should continue its path until the fuel runs out.

Now what if it was a temporary loss and you regain signal?  

You are flying directly towards the clubhouse at 20 feet full throttle when it loses signal.

Would you prefer throttle hold of throttle failsafe?

Hopefully these examples will get you thinking because there is no right or wrong.

Real example:

I was once close to the pilot area and had just started my nitro helicopter. I picked up my transmitter and when I clipped in the neck strap I accidentally turned off the transmitter. Because of the failsafe I had set (idle and level swash just above neutral), it just sat there idling away. I have since changed my clipping of the neck strap procedure so instead of clipping down, I clip up, but I digress.

What can’t it do.

If the aircraft has a total battery failure the RX failsafe feature will not work. Some radios have the ability to go into failsafe when the battery goes low, but if the battery lead breaks, then there is nothing you can do.

How can I check I have set it up correctly?

If your aircraft is electric, then ensure that blades / props are removed.

If its fuelled, then obviously don’t start it.

Then turn on your transmitter, then your receiver. Wait for it to initialise and check first to make sure all your controls are working correctly as you expect. If it looks good, then move both sticks on the transmitter to the upper corners (I do this to ensure the throttle is active) and then turn off your transmitter and look at the aircraft to see what happens.

For a maiden, I set the throttle only because I have no idea if its trimmed correctly, COG optimal etc.…

After I have trimmed the aircraft to where I am satisfied, I then reset the failsafe to my preferred positions. (on my spectrum DX7 this means rebinding)

Minimum Recommendations

Regardless of what you decided to do, I would strongly recommend that as a minimum you set the failsafe on the throttle. For me I like to set it a tiny bit above idle on fuelled aircraft, and off on electrics. this way if it is just a temporary loss the motor will still be running when signal is recovered.

How do I do it?

There are so many radios out there so the best way is to google it, but I can tell you on my Futaba radios it is set from the transmitter, and my Spectrum DX7 it is set at the time of binding.   This is an important point, because sometime when setting up a new model I first bind, and then realise the throttle channel is reversed so I change it.  But this means the failsafe position for throttle will be full noise.

And of course ask a competent club flyer or an instructor. There are a lot of members with a lot of knowledge and different ideas.