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Old Dec 20, 2010, 09:56 AM
xlcrlee is online now
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Zurich
Joined Apr 2006
4,891 Posts
Tuning Summary (+ recent application thereof)

I set-up a 5888-R I bought (& stored) this summer. It is now exceptional, with both rotors strobing at the same RPM and the heli handling like a Formula-1 racecar.

BUT, it was at first very problematic, unstable & uncontrollable. One servo kept locking, NO adjustment held. Getting it all sorted out took ca. 10 hrs over 2 days ....

The finally-found root of these problems was very bad voltage-regulation! The motors easily get HOT in the first 30 sec! The servos drove to the top: the one that kept locking I had to de-mount, then VERY carefully bend & reposition the nano-wipers (lots of fun!!).

In the end I used my well-proven set-up, having to continually RAZOR-sharp re-track as I changed things (often req. re-pitching one blade of a set) >

added ca. 1 pitch to BOTH rotors

upper rotor ca. 4 mm tip-play
lower rotor ca. 3 mm tip-play
[upper is larger fo allow Re compensation w/ RPM incr.]

NOTE: in this (& most) good coax's, the lower rotor properly has ca. 15 - 20% more pitch than the upper (see my thread on the subject).


Coning Angle:

The more positive coning angle, the less stable (less self-stabilizing) the rotor.
[heli airflow opposite from fixed-wing!!]


So, to get this "new" over-driven 5888-R under control, I flattened the lower rotor's coning angle to reduce its control authority such that the upper edge of the rotating blades are now almost horizontal. I also slightly flattened the upper rotor to incr. its stabilizing effect.

NOTE: too large upper coning angle > rocking in fast banked turns; too large lower coning angle > spinning-in in fast banked left turns.

Thus have I now gotten this HOT "new" one very quiet (acoustically & motion-wise) and stable in hover AND fast flight, with just enough control authority to make it jump when I wish. I generally drive it carefully, smoothly & precisely like an F-1 car! In "Low" mode it behaves like a "normal" 5888 in "High" ....


SUPER!

Lee
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