Poll: DJI compatibility with your favorite RC equipment (PPM, D-Bus or standard RX)

hexacop

HexaCop
Hi everyone,
I hope all of you had a good flight today and nobody of you lost his valuable copter due to any hardware or firmware issues.
Almost on daily basis there are people reporting bad news of copters not working as expected, pilots loosing control or even crashing.
For sure there are many reasons for a crash be it hardware or software faults or even incompatibilities between the equipment used.
Currently there is a big discussion on the german FPV Forum about using PPM receivers, DJI made some statements that they did never tested any receivers like Jeti or Graupner / JR in PPM mode and they recommending to use Futaba only. Some dealers started already to alert customers not to use PPM receivers but only traditional receivers.
Many people who have been using PPM receivers have real doubts now to continue using their PPM receivers and risk a crash or the loss of the copter.
As usual there are a lot of rumors but not many facts available.

I've tried to create a survey to capture recent copter configurations.
The purpose of the survey is to evaluate if there are clear correlations and incompatibilities between certain RC equipment and DJI multicopter controllers.
This survey is used to capture crashes or incidents with copters due to the loss of control by the pilot.
Situations which has been caused by faulty hardware related to: motor, ESC, prop, battery or any other fault not related to the compatibility of the RC equipment should not be recorded here.
Basically we try to capture those incidents when it was not possible for the pilot to control the copter with the transmitter, regardless if the copter crashed, flied away or if he was lucky to land it safely after the incident.
If you did not had any crash or any problem till now, please still respond to the survey to confirm the positive experience with your setup.

This is the link to the survey:

Evaluation of the survey:

Thank you for participation!
 

soler

Member
Great work, Can this be made sticky to stay on the top of the forums.


For the results you will need to do some number crunching as currently the results are shown as a total of each data set, currently it will not show for example if PPM is any better or worse than S.bus, only the total people unsung S.BUS or PPM.

Thanks
 
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hexacop

HexaCop
Yes sure we will need to evaluate the data from different views, right now it does display the data straight forward out of the spreadsheet, without any logic behind...
Would be good to stick it for some time and hope the forum moderator can help with that request?
 


hexacop

HexaCop
Last night I could finally reproduce some bad behaviors which may have lead to this rumors that DJI products may not work well with some PPM receivers.
It was reported a few times already that there are certain circumstances in combination with PPM receivers which lead to channel glitches.
Even I had seen some time ago some channel jumping in the Naza assistant, but then I did a firmware upgrade of my JETI RSAT receiver and all was good and worked perfectly.
Now some other people have reported a crash and after they investigated the cause of the crash they could see this glitches in the WKM assistant.
Also in that case a Jeti RSAT2 receiver was used. The recomendation they got from DJI dealer was to use Futaba and not use PPM receiver anymore.
I have tried to reproduce the cause of the problem by diagnosing the PPM signal with different PPM settings and receivers.
Here you can see a video of the PPM signal with Jeti and JR / Graupner GR16
In the video you can see how the Jeti PPM signal is generated by the Jeti RSAT and even if you choose a 'short' frame length the PPM signal remains valid as some or all channels reach 100% limits. Even when the number of channels increase, the PPM frame length is expanded dynamically as needed. The synch frame of minimum 4ms which is needed to ensure the synchronization of the channels is always maintained.
Nevertheless there must be some PPM settings which could cause the symptoms described above and I could identify those settings which do not work well and are causing at least one channel to jump between -1000, 0 and +1000.
See next video:
Jeti RSAT2 firmware 3.11 Settings which lead to this glitces
Output Period: AUTO
PPM Pos
Output Channels PPM 8
You can verify that easily with your Naza assistant...

Recommendation for Jeti receivers is to use a fixed frame length of 20ms or 22ms with PPM 8, that has been proven to work without any issues.
As you can see in the first video, the JR Frame is very similar except the polarity which does not make any difference, both are being recognized as a valid PPM signal by the Naza controller.
 
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