More on my X-rotation helicopter. I think the motors revving up and down while holding the chopper in your hand might be a red herring. I did some reading on piezo gyros and they sense angular velocity (speed of rotation). It may be that the model is trying to rotate slowly while you're holding it and is sensing no rotation so it tries harder. This is backed up by the fact that it doesn't seem to happen while it's flying. Although sometimes it starts spinning rapidly for no apparent reason.

Anyway, I had a breakthrough a couple of days ago when I re-balanced the flybar by wrapping a short piece of wire around one end and also replaced the whole tail section with a rod and cardboard fin (set up vertically like a rudder) to resist twisting. Now it will hover without me even having my hands on the controls if trimmed properly. Still having to fix it every couple of days or so from minor crashes. Damn it having no spare parts available!