Good news...
. Just as I was about to write the Gyro off, I rechecked my notes and realized that the problem started after doing some changes to the throttle
curve in normal mode. Without realizing, I had set things up so that the heli would hover just before the curve went flat. Apparently, the governor mode of the ESC (a
Turnigy 85A ESC/SBEC, but this is a budget machine) did not handle that too well, likely causing power to fluctuate rapidly, sort of like a nitro engine misfiring. I think the CSM gyro did not react fast enough to make
that noticeable, but the JR did. As for why it seemed to disappear with time, I am inclined to think that as the ESC/motor warmed up, I had to apply slightly move throttle/pitch to hover, and so I moved into the flat section of the curve.
So, once I changed the curve to be flat at take off and hover, the jerking disappeared as well.
The silver lining is that I learned about the effect of control arm length on the gain.
Thanks again for the input. Jim, If I'm ever near your neck of the woods I'll make sure to pay a visit to your store.
Alberto