they are very very hard to fly. i've messed around with a cheap electric one and destroyed it
whats so difficult is staying in control. it's easy when you stand straight behind it and don't turn it at all (yaw axis) but once it changes directions it's almost impossible, for me at least, to keep track of it and know how to control it.
that's why in this video he can control it like that. the whole time he tries to keep it generally in one angle. still hard as hell... but to do that upsidedown doughnut thing you gotta be a machine lol
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