Have a look at these two photos. I have a Samsung Galaxy Tab S2 (T819) running Litchi, controlling M2P, whose gimbal is controlled by Goggles RE. I am holding the tablet facing the camera so that the response of the gimbal and live view image is shown in the photos. Here’s what I did.
Problem to be solved
Tablet didn’t properly connect to RC and failed to show live view with either app (DJI GO or Litchi). When I tried to change USB mode to MIDI or RNDIS, as suggested by some, a dialog pane kept popping on or off asking whether DJI GO or Litchi is allowed to use USB. The dialog pane appeared for a fraction of a second, then disappeared and popped up again forever.
I had tried downgrading the OS to Android 6. When I bought the tablet, it ran Android 5, and worked perfectly with my Phantom 4. When Samsung updated to Android 6, the USB problems began, but they could be solved by changing USB mode to MIDI or RNDIS, shutting down the tablet and restarting it when everything else was ready. After Android 7 update this workaround no longer worked. A Youtube video by “Musing of a Man” suggested using a USB 3 cable (with a blue A connector and a C-to-B micro adapter at the tablet end). This worked for me – but only once.
This is what works for me systematically
One-time preparations
- I’ve downgraded the tablet from Android 7 to Android 6.0.1. This is probably not critical as it didn’t solve my problem. But now that I’ve done it, I’ve disabled automatic updates and keep the tablet as it is now.
- Install current versions of control apps (DJI GO and Litchi for me).
- In settings, turn on Developer Settings.
- In settings, assign all permissions to your control apps (DJI GO, Litchi …) Surprisingly, this step got be beyond the repeating dialog pane which requested USB permissions. As I have now dedicated my tablet to drone use, I only have drone-related data on the tablet. You may try whether this step is necessary for you and revoke the permissions you don’t want to grant.
- In settings, ensure that no control app is set as default. If you this, when you turn on the tablet, it asks if you wish to run DJI GO or Litchi, and if “This time” or “Always”.
- In developer settings, set USB mode to MIDI (or RNDIS). These settings are certainly wrong and the tablet selects an appropriate USB mode.
- Exit settings and turn off tablet (hard shutdown).
- Connect tablet to RC but don’t turn them on yet.
- Turn on AC and RC (in either order).
- After you turn on the RC, it begins to charge the tablet. Wait until the charge indicator (battery icon) is shown.
- Now turn on the tablet. (If you do it before the charge indicator is shown, the tablet may miss the press of the power button).
- Tablet asks if you wish to run DJI GO or Litchi, and if “This time” or “Always”. Choose your app and tap “This time”.
- Your app should now connect to the RC and AC (with Litchi, it may take about 10 seconds for the live view image to appear).
- Turn off AC and RC (assuming you don’t want to continue with another battery).
- Disconnect RC from tablet.
- In developer settings, set USB mode to MIDI (or RNDIS). Exit settings and turn off tablet. Repeat this step before your next flight if in the meantime you use the tablet for other purposes.
