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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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Hi Micha ,

so tomorrow i'll programming the new firmware on receiver . This evening i going to a meeting and i need to produce a signal inverter and haven't time to do .

Tomorrow morning we continue the test and try to understand the problem. 

I see around and i check a lot of guys that had problem with that receiver .

Here there is a issues again open on PX4 github ... Roberts told in the forum that after destroy his helicopter stop to test that radio receiver also after the patch .

So i have great experience with Taranis FRSKY SBUS don't have any kind of problem with that kind of receiver it a lot better respect of dr4r-ii . 

But tommorow check the patch and update you about our result with new firmware . The old one work without glitch for 1 hour.

Good morning Roberto.
The kind people of Frsky have emailed me the original FRsky firmware. I have sent you an email with the file so you can flash back and forth if that would be necessary. I will now reflash one of my receivers to 18ms and redo the table experiment. I will keep you posted on my findings.

Roberto, you do not have to flash your rx with 27ms firmware. I re-flashed mine to 18ms and still no go on both copters. I drove to a friend to borrow his sbus X8R and it works perfectly on sbus. The strange thing is that you where not able to replicate it on yours. A solution would still be appreciated as i have 5 of these receivers and the X8R is not mine. I tried the 18ms on the pixhawk and it works perfectly, same for a nanowii.

Hi Micha , i flash my Dr4 II with 27 , found where is the problem on the standard ppmsum driver that is the same of px4 - pixhawk . I change the PPM_SUM_MIN from 2300 to 7500 .

Now i don't see iusse until 1 hour of work . 

My impression is that receiver is out the standard and could have same glitch sometimes. 

If you check in Skype you have new firmware with the patch try it and send us some feedback .

Normally if you don't set failsafe on radio during fly don't have understand to have a glitch but if you have it active start the procedure of land.



I have done some more digging in this Github link you provided to me.

From this discussion here it looks to be a noise issue.

Possible sollutions: adding a 1K0 resistor in series with the CPPM signal


1) A 10nF capacitor from the PPM input to ground, as close to the connector as possible (on the pins on the bottom of the board would be ideal). If this helps but not enough, increase to 0.1uF (but remove any series resistor if you do this).

2) Shielded cable for the PPM signal from your receiver to the PX4. One half of a stereo cable, or cable from an old pair of headphones will do. At a pinch, use discrete wires and twist them around each other; try to get at least one twist per inch. You can buy pre-twisted servo cables, which may also help. (Mbrain multiconnector issue?)

Maybe some experiments in this direction could result in a permanent fix.

The option is always open for me to sent one of my offending receivers to your office. It is clear that your copy takes longer then mine to show the issue. Mine shows it within minutes most of the time.

Now for something else: there are some references to the D4R-II recievers in official px4 documentation: (by example, including references to the 27ms fix)

or in this official ardupilot documentation. (the howto youtube video is done with a D4R-II)

Given that there is no difference in the pixhawk/px4 code and yours it must be Mbrain hardware related.

With is confirmed again today with a new experiment by me with the Pixhawk showing no problems at all.
It is not a problem for me to buy some X8D's to get flying but that will not solve the problem for you as the D4R is fast becoming popular among drone pilots. This issue will come back to haunt you. ;)

Anyway, goodnight guys.

A little follow up on the failsafe issue. I am beginning to suspect several of the multi connection red wire 10 cable leads of my Mbrain are bogus. Can i buy some to check this out? 4 would be great so that i have some in reserve. If you do not sell them separately a link to a seller who has them would be great. ;)

Hi Micha,

yes we can sell send a mail to with the request.



I wanted to know if you had solved the problem of fail-safe mode PPMSUM,
I have the same problems as the vbrain goes into failsafe even with the new firmware 3.2-RC4.
The same configuration as TX and RX Turnigy, PWM to PPM Encoder Module installed on a APM2.5 firmware 3.2 RC4 not problems.
I measured the PPM signal with an oscilloscope, and the beginning of the synchronous start the new sync there are 18ms with 8 channels transmitted.
Unfortunately I can not do an upload of the firmware 3.2RC4 PWM because the Mission Planner gives me error.

regards Fabio

Hi Fabio ,

the failsafe work on ppmsum but work fine only if the Drone is armed when is disarmed the failsafe don't work.



Hello Roberto,
As for the fail-safe radio the drone is armed and ready to take off with the GPS 19 satellite, so many that are taken off time to pull the cart from the ground that the drone went into failsafe radio and landed with my amazement did not understand what was happening.
Enters fail-safe mode randomly and not given in time, loses synchronism ppm although the timing that I measured is stable at 18ms.
It would be helpful if the beeper emits rhythmic beeping when you get into fail-safe mode to get a quick understanding of what is happening.

PPM is not fixed and has never been fixed. Of all my flight controllers the mVRbrain is the only one who has problems with it. After many hours trying to find the reasons i eventually gave up on it and was forced to buy Sbus recievers. A pricy solution. They just work fine. The issue is hardware related. Now i suspect my red 10 cable connections. By now i have 2 of them with bad connections. They fail to  pass 5 volt to the reciever. I emailed 10 days ago to request where i can buy some but have yet to receive an answer.
Do not use PPM now and be very careful not to engage RTL in mission planner. A gps glitch while it randomly goes into failsafe would be catastofical and could lead to a fly away as you do not have the ability to use your switches to get out of it.

Hello Micha,
I think it's a software problem, I visualized oscilloscope with the input signal to the processor pin the signal arrives clean and not distorted. My problem now is that I would like to load the firmware in PWM, but I can not for the error that gives me the mission planner in the upload of custom firmware.
Sob! Sob! :(



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