R/C Failsafe Information

[DanPBP]

Hello Guys,

I've been driving R/C cars for more than two years now. I love this hobby and I made a few circuits to turn on/off brake lights, fog lights, etc with some 12F675 PICs.

Now, I'm trying to understand how a failsafe works. I know that a servo receives a PWM signal from the receiver, and that signal is between 100 and 200, being 150 the center (read with PulsIn).

Anything outside that range is not good and the failsafe circuit must work at that time braking the car or whatever you programmed it to do.

But, I was reading the PWM signal from the receiver when the transmitter is OFF, and the PWM signal jumps between 0 to 255. I mean, the PWM signal can be valid or not, when the transmitter is OFF.....

So, how do you know that the transmitter is OFF? I mean, is there some kind of algorithm to find out that the PWM signal is actually coming from the transmitter when it's ON and is not a random PWM signal when the transmitter is OFF.

Thanks!

Daniel.

[Acetronics2]

Hi, Daniel

IF signal lost ...

Pulsin returns:

1) with glitches : value outside the 0.8 / 2.2 ms range. ( some can be inside this range ...)

2) without glitches : ... 0 is returned. see Manual for use of "Define Pulsin_Max".

With some little brain storming, failsafe works really fine !!!

see here : http://aeronews.free.fr/archivesarticles/19-electropratique.zip

nice and relevant example ... isn't it ???

Alain

[Squibcakes]

Not sure what system you are using, but on my spektrum 2.4Ghz, the fail safe settings (stick positions) are set when binding the receiver to the radio.

If in the event the receiver loses the signal - it moves the servos to the fail safe position (as set when bound).

[DanPBP]

I'm using the stock AM 27Mhz radio from Traxxas. It doesn't have a failsafe built in.

And, I already have a Duratrax failsafe on my truck, but I wanted to research a little more to understand how it works.

I mean, I'm not planning to replace a $20 failsafe that works great! But, it would be nice to know how to make one and "see"' the inside magic. :)