If there is any one thing that will ground a helicopter, it's vibration. In the coaxial helicopters, the fly bar HAS to run in a true circle with the shaft showing no wobble at all. When the inner shaft wobbles, the fly bar may look straight when it's stopped, but at speed it is running in a double circle (flybar is spinning and the center shaft is also moving in a circle) and that actually bends the flybar at flight rpm. I took a stop action photo of mine once and that's how I found it. The darned flybar was bent about 1/4 inch from straight - but when I stopped it the flybar looked perfect. The only indication was vibration.

When you eventually move to a single rotor helicopter with a tail gyro, vibration will defeat that gadget. Get used to finding and fixing vibration. Perfection isn't required, but the better it is, the better it is. Ya know?

Happy Thanksgiving!
Soloboss