Advanced Rotors too weak?

tried to build a vertical arm using the Advanced Rotors and large conveyors for small ships, and the natural gravity just make the arm fall to the ground an unable to retract or go up. even when full torque and full breaking torque

Tested on planets too, same result. Although I found a workaround using Atmospheric Trhusters, but Im still thinking that this rotors needs more strength

a video to shown this problem

 

It may have something to do with how much weight you have on it? Either fewer drills, or double up the rotors in wishbones. Or both?

 

nahh ... i also find the Rotors not powerful enough...