My Drone has lost power? (WLtoys v686g)

I just wonder, it must be something in common with all motors, or the drive behind the motors. The latter is hardly likely, as there are separate outputs from the FC to the ESC's. If the Oscillator for the CPU in the FC has dropped in frequency (Bad connection or faulty component) then the frequency presented to the ESC's would be lower too, so the props would spin at a lower speed. I wouldnt try to fix that, its all surface mount stuff, and you need special tools for that and also a circuit diagram. The easier fault to fix is a dry joint on the main supplies to the ESC's. If for instance the XT-60 connector has a bad connection on the wire side of the connector, one could detect a heating effect at that point. One then can either cut and remake that side off again. Check that battery connector, hope it is that, as it is the cheapest and easiest one to fix!

 

At least one motor is worn out. Brushed motors in quads don't last long. The flight controller is doing it's thing keeping the quad flying and compensating for the weak motor.