Wow nice! Do you want the pitch of the blade to increase, when it is exactly above the part pulling the spring down? Because I guess you have quite some lag due to the elasticity. At least that's the problem I ran into, even though I was not using springs. Mine uses braces and hinges (maybe a little heavy). It technically works, but is impossible to fly for more than a few seconds. And that is, because pitching the blades for a roll also affects pitch of the helicopter and vice versa, due to that lag. Also, another monocopter of mine had the same problem, when moving at a certain velocity, one side of the rotor loses its lift and begins to roll the helicopter. Quite natural. This could be prevented by a faster rotor rpm, but that blew my blades away and also would make cyclic pitch change even more delayed and structurally demanding.

From what I see in your video, you don't have that problem much (maybe the roll), and I guess downloading your file wouldn't help me understand much of how you attacked those two problems. Or didn't you run into them in the first place, because of some randomly lucky arrangement, where everything was balanced to begin with? I thought that delaying the blade pitch control by about 90° would only shift control directions, but then it would be quite controllable again. Never adjusted averything for it though.

Also, can you explain, why the engine keeps working? I guess the springs keep putting energy into the system for some reason, but I am not sure.

And here you got a challenge: Go and add 2 axis cyclic pitch change. Ideally with a constant pitch offset, by moving your "control disk" up and down. The second axis can be added quite easily I think, only replace the hinge in the middle by two hinges moved to the side a bit, connect them with braces to the spring attachment points, and use the steering elements to rotate the whole connection bar in between, including the wheel.


Finally, my given up project:

EDIT: Now, that I think about it, my helicopter also tried to auto-correct, but it couldn't recover. With a different mass distribution, probably higher, like yours, mine might be stable as well... (But I'm ooonly building inside the bounding box. )