Pairing up the phones is a constant struggle for every session. There are too many guesses, try and errors. So I decide to write this down as the team SOP.

Prerequisite

• The Robot Controller (RC) phone should have the latest "FTC Robot Controller" app.
• The Driver Station (DS) phone should have the latest "FTC Driver Station" app.

Device Name

It is recommended to use dddd-RC and dddd-DS to name them where dddd is your team number (8421). It seems that other people have used dddd-B-RC and dddd-B-DS to name the second pair of phones. This secondary setting needs to be proved working on the latest app before adopting.

Setup

1. Set both phones to "Airplane" mode, then turn the Wifi back on.
2. Make sure the RC phone doesn't connect to any Wifi network. Forget any network that interferes with this step.
3. Go to Wifi -> Wifi-Direct. The RC and DS should be "Peer Devices" to each other, and connected.

https://www.youtube.com/watch?v=2zxu2ynwE48

4. Start RC app. You should see "Network: active, ...". If "..." is "connected", you are done. Otherwise, continue.
5. Start DS app. Go to Settings -> Pair with Robot Controller, and attempt to pair with RC phone.

This step can be very problematic. If you believe the phones are named and wifi-paired correctly, but the apps are not pairing, you need to reboot both phones by following the post below:

https://ftcforum.usfirst.org/forum/ftc-technology/3701-technology-tip-wifi-direct-pairing-long/page2?4690-Technology-Tip-WiFi-Direct-Pairing-(LONG)=&viewfull=1

The apps appear to have some issues forgetting older settings. Reboot both phones should do the trick.

6. On DS app, you must see "Network: 8421-RC".