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Old 01-03-2013, 01:15 AM   #2 (permalink)
Dr. M
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Default Initial Tuning & Maiden Flight

Before you fly for the first time Stop! Examine your setup one more time, make sure everything looks and moves right.

In particular, if your Collective Range number is lower than 60 and you still have 12 pitch at the top, your swashplate servo arms are too long: move the linkage balls one hole closer to center. Conversely, if the number is higher than 80 for 12 of pitch, your swashplate servo arms are too short: move the linkage balls one hole further from center.

For you first flight you'll want to take it easy and make sure nothing bad happens. I recommend you set your Tx tail gain to whatever value reads 36 in the Monitor screen of the PC software. Set the Roll and Pitch gains on the main screen to 25. This will help prevent possible violent oscillations caused by too much gain.

Deadbands

CX and ZYX firmware older than 3.5 had a bug in the way the stick deadband was implemented ("Deadband RC"). The defaults were far too high and, together with the bug, caused odd, twitchy, or jerky behaviour. A simple solution is to reduce this parameter to a value no higher than 15, or else upgrade the firmware to ZYX 3.5.

The other parameter, "Deadband Gyro" refers to the way the gyro talks to the servo and functions correctly. Keep this one at default, or the lowest setting you can get that will not cause your servos to overheat.

Maiden Flight

Spool up with your lowest HS and pick up into a hover 10-12ft AGL. If the tail isn't wagging, give a few stabs of the rudder stick. Observe for any wobble or instability in the rotor disk. Give some small, but quick stabs to the cyclic stick (both nick and roll). It may feel pretty mushy, but the disk should not wobble. If it does, stop. Something is wrong - either cyclic servo arms are too long (see above), servos are too slow/weak or you've got some serious binding in the head mechanics.

Let's say the tests above went well, switch to your highest HS. And repeat the tests. Decrease your tail gain if you get wags, but you should not need to decrease the cyclic gains. If the tail is stable, increase the Tx tail gain a few points at a time until the wags just start appearing, then dial it back 2%.

Also, start increasing cyclic gain 5 points at a time and test by giving quick stabs to the cyclic stick. Keep increasing the gain 5 points at a time until you see the disk wobble after quick stabs to the cyclic stick, then go back down 5 points.

By this point you should have a pretty solid foundation to move on to advanced tuning. The cyclic and tail gains should be pretty close to optimal, though perhaps a bit on the high end, we'll tune them next.

Fine-tuning main gains

Finally, do some FFF and decrease the tail gain a bit if you hear it wagging. Also watch the disk for any signs of wobble. Particularly, fly some gentle FF descents with the disk unloaded (0 or slight negative pitch - think autorotation, but don't turn off the motor): if you see any wobbling, drop the cyclic gains 3 points.

Final note: optimal gains depend on your servo speed/accuracy, ball-to-center distance on the servo arms, HS, as well as overall geometry, mechanical condition and setup of the head.
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Last edited by Dr. M; 01-07-2013 at 01:31 PM.. Reason: added info on deabands
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