Bought the spark about a week ago. Overall, like it a lot. But was a bit disapointed with all the issues with the OTG cables. Clearly this is not a 100% complete product as far as software goes... I understand DJI has a lot going on at once... But I expected a bit more from a retail product.
So, the goal was quite simple:
Run the DJI GO android app, in VR mode. I know you can use Litchi and get VR mode going, but I found 2 main issues with Litchi:
a) OTG mode for the Spark is not fully supported. I am not quite sure how it would react "in the air"... But for sure the Battery / RC Signal and Video Singal indicators did / do not work. This is not to be confused with the lack of telemetry that you get when using a newer version of the DJI GO app and the Spark via OTG. The issue is similar, but seperate.
b) Even with the OTG cable, the Litchi app has quite a bit more lag then the DJI GO app. I would guess about 0.5 sec more.
So, I am currently running the latest firmware on all "hardware" (RC + Spark). And DJI GO 4.1.15. When using the OTG cable, I get a fully functioning quad. Everything works. Not a lot of monkeying around with "plug this in, after that...". Pretty much the only thing that I need to remember is to plug the OTG into the controller after the green light shows up on the controller.
Now, how to get the DJI GO 4 app to load up in VR Mode... Even though VR mode is not supported. I come from a heavy software development background and thought s**t, this is Android... I'm rooted and all... This should be possible on my S7 Edge.
I wont go into details on how I got it running... You will need to have a rooted phone, with xposed running. And then turn on the app2vr module. NOTE : I had to switch roms on my phone. This is obviously phone / rom specific... But with my last rom, app2vr did NOT work... It would freeze when loading up. I did an adb logcat and looks like my rom had an issue with the OpenGL modules (EGL?)... I'm not really an android internals expert so I did not fumble around TOO much trying to fix it.
Also, app2vr is obviously in beta / incomplete state. Looks like the developer abandoned it about april of 2017. So there are some issues, none that are "fatal" though. You will probably want to disable the gyroscope in your phone while using it for FPV. Otherwise:
a) Your phone is super sensitive as far as the gyro goes.
b) The app will often times show "the screen" to the right of my head.
With the gyro disabled, it shows up dead center and does not move around. To disable the gyro, I use yet another xposed modue:
lvl.2
lvl.3
lvl.1