With two models supplied immediately the gears slipped off on the motor shaft,
so that the lower propeller does not rotate. Readjustment does not help.
The helicopter is not airworthy.
Other customers report this error,
Therefore, it seems likely that this is a series fault.
Amazon has taken after my second complaint the article for review from the sale.
Overall, Amazon behaves extremely customer friendly and absolutely correct in rescission and refund!
Thank you for this service.