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It means the motor must be able to be removed from the helicopter so the helicopter's weight can be checked.

In indoor freeflight lingo, a rubber band is the "motor". So yes, your rubber band needs to be removable/separatable from your helicopter.

But if it wasn't removeable then how could you wind it? THe only thing I can think of is to turn the rotors but even that would be incredibly slow and inefficient. Isn't it common sense to remove it?

I spin the body which is connected to the rotors. The rubber band is inside and attached to a hook. It's a really simple design.