Dam G11 controllers and motor stalls! It a common problem. my guess is that the design is a bit marginal and the driver chips are slightly overloaded, and over time this causes an increase in the drive impedance.
But then it could be a power cable that is too long, or not fat enough. Measuring the voltage is only useful if you can measure it at the controller when the motors are stalling. It might be drouping.
Not much the chinese can do about that I'm afraid
Although they could probably make a better and cheaper DDB.....
Still thinking about AF. I would be quite keen, so better start saving now, and you guys better keep your swine flu in check...
Cheers