DonMilne:
I'm not convinced that the radical change from free rotation of both halves to totally locked is solely due to friction - in fact I thought epicyclic gearing was low friction by nature
I wasn't talking about friction within the gearbox but about the resistance to turning that is inherent in any electric motor with permanent magnets. When that resistance is multiplied by the overall ratio of the gearbox it won't be trivial.
And I agree, I don't have a definitive answer.
...R