It's not really a quadcopter since it's 2d, but same idea. One ApplyForce is done at each end as shown by the orange lines, and this is the only control output. There is one PID controller to alter the ratio of force between the ends, and another PID to alter the total force output. Surprisingly it works fairly well.
...
https://www.youtube.com/watch?v=2DTw9FJ5sAY
Wingwing setup info page: https://bit.ly/393gbFC
Nikola's video: https://youtu.be/fnGywBarXRs
4:20 Initial impressions of Nano talon
7:24 Helpful info on endurance builds, and Wingwing specifically
9:47 Parts used
13:02 Nano talon maiden flights
17:43 Endurance test overview
19:13 Nano talon test run
20:55 Nano talon result graphs
28:24 Wing wing test run
30:33 Wing wing result graphs
33:29 Result comparison
35:41 Confusion about Nano talon result
38:40 Summary (on-screen text)
...
https://www.youtube.com/watch?v=wbTGNJjUQtU
This video explains the changes in version 1.2 of the R.U.B.E Box2D editor.
See these links for tutorials on using the editor:
http://www.iforce2d.net/rube/tut.php?n=1 The workspace
http://www.iforce2d.net/rube/tut.php?n=2 Documents and views
http://www.iforce2d.net/rube/tut.php?n=3 Edit modes, selecting, and the cursor
http://www.iforce2d.net/rube/tut.php?n=4 Panels: Items, properties, script
http://www.iforce2d.net/rube/tut.php?n=5 Basic manipulation: translation, rotation, scaling
http://www.iforce2d.net/rube/tut.php?n=6 Editing bodies
http://www.iforce2d.net/rube/tut.php?n=7 Editing fixtures
http://www.iforce2d.net/rube/tut.php?n=8 Editing vertices
http://www.iforce2d.net/rube/tut.php?n=9 Editing joints
http://www.iforce2d.net/rube/tut.php?n=10 Revolute joints
http://www.iforce2d.net/rube/tut.php?n=11 Distance and rope joints
http://www.iforce2d.net/rube/tut.php?n=12 Wheel joints
http://www.iforce2d.net/rube/tut.php?n=13 Prismatic joints
http://www.iforce2d.net/rube/tut.php?n=14 Editing images
http://www.iforce2d.net/rube/tut.php?n=15 Script logs
http://www.iforce2d.net/rube/tut.php?n=16 The action menu
http://www.iforce2d.net/rube/tut.php?n=17 Custom properties
...
https://www.youtube.com/watch?v=lwG078IqnBE
Rather impractical it seems.
http://ardupilot.org/plane/docs/guide-tailsitter.html
https://discuss.ardupilot.org/t/dual-motor-tailsitters/15302
...
https://www.youtube.com/watch?v=hstkV_uUs28
And they were mostly right, but not always.
Thrust test stand info: https://github.com/iforce2d/thrustTester
Spreadsheet: http://www.iforce2d.net/sketches/propBrakingResults.ods
...
https://www.youtube.com/watch?v=Tn1OQui_9S4