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PPM failsafe issue Dr4 II with 27 (WIP but don't safe to use DR4 II better to use SBUS receiver )

Probably related to the Failsafe problem, but i have an issue with 2 different copters running micro Vrbrain 5.1 and D4R-II 27ms receivers(3.2 rc2) connected with ppm. Both of them go in failsafe after a while. No Rssi problems on my tarranis. In the mission planner failsafe screen i can see the signal dropping sometimes and coming up again after a few seconds. Since these are to separate machines i am at a guess what would be the reason. Needless to say this is serious issue for me. Any ideas?

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I am not sure if it is a software issue. But it is good news that the signal is clean at the board level. In that case 2 of my cables are still bogus as they fail to pass 5 volts. I have spend a day in corporation with Roberto to find a solution. We have tried several different versions of software, . But the fact that pixhawk works fine is strange. I used MP 1.3.7 24027 to upload custom firmwares Roberto give me without any problem. I presume you have read this?

As you mention you want to use pwm i assume you are not using a FRsky D4R-II. What receiver are you using if i may ask?
I have to go do some aerial video work now. I will be back in the evening.

Hello  Micha,
I've finished doing tests on  VRµBRAIN, I focused on the levels of tension between the receiver and the  VRµBRAIN.
I think I've solved the problem, the first once armed drone went after a few seconds in fail-safe, after the change, the drone once armed remained more than 25 minutes without having a failsafe. Tomorrow I make the latest evidence and then I'll give you the news, I hope positive and definitive about changing that I did, for my problem that similar if not the same as yours.

For the PWM using a receiver Turnigy 9X8C. 
Greetings and good night

That is great news. Tnx for looking into this.

Hi Micha,
Today I tried the change I made ​​and it worked out very well OK (Video). The modification consists of placing a resistor in series to 10-15Khom PPM signal, this decreases the voltage and the current flowing without saturating the input.
Usually the outputs of the receivers or PPM decoder, are 4.5 / 5Volt and strangely the entrance of Vbrain is 3Volt, it should be 0Volt is an input, I think it was programmed in mode INPUT_PULLUP.
I also tried a circuit Bi-Directional MOSFET Voltage Level Converter 3.3V to 5V but it did not work.

Tomorrow I will test higher to see if the change is safe, and that you do not repeat the fail-safe.
I hope that this change is also useful to you.
I believe that the inputs directly connected to the cpu and not filtered through the resistors in series with the protection and long connections can create some mismatches.
Emile You could do a test and put the input pin pullup not high, but low by software, it is only a test.


There is a problem with the video but it sure looks you are on the right track. ;)

I copied the link wrong video sorry.


Well, my FC and RX combination would have surely gone into failsafe in that timeframe. We may need some more testing to be sure and incorporate the fix in a next revision of the Mvrbrain.



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