[JensR]

The gearbox to which the gearmotor is attached is a worm drive, which cannot be back-driven, so the circle will stay in position.

For the full-scale machines a powerful circle rotation is a major selling point, ideally you want to be able to rotate it with a full blade.

I, too, wonder whether this motor will be strong enough, after my own negative experience as a circle drive, but Hemi has a higher reduction, as far as I can see, so while slower, it should have some grunt.