Tricopter: rear boom bounces as throttle increases. When airborne one inch, goes into flat spin.

[GoogleCodeExporter]

What steps will reproduce the problem?
1.Mode: stable.
2. As throttle is raised, the rudder boom begins bouncing. No other booms 
bounce.
3. When airborne one inch, the tricopter goes into a flat spin. 
4. Apparently unrelated issue: The rudder motor control is reversed.  I 
reversed it back in the Tx. The apm now arms when I pull the stick to the left 
and then it works normally. Disarms when I pull to the right.
5. Rudder servo is powered by the rudder UBEC.  Only the signal wire runs from 
the rudder ESC to output #4.  Only the signal wire runs from the servo to 
output #7. Except for being reversed, the rudder servo works normally…but is 
very sensitive.

Attempts to fix:
1. Replaced rear prop four times with carefully balanced props. No improvement.
2. Ran rear motor without prop.  Perfectly balanced at all throttle levels, but 
the rear boom bounced when I installed a prop.  Two weeks ago,  I used the same 
motor with a KK2, the boom did not bounce. The entire tricopter worked 
perfectly with a KK2.  The rudder control was not reversed with the KK2.
3. Replaced and balanced rear motor.  Without a prop, it ran with a very, very 
slight vibration. Installed a carefully balanced prop.  Rear boom bounced and 
tricopter went into a flat spin.
4. Lowered “Stabilize Yaw” P value from 4500 to 3500.  No effect.  Still 
bounced and went into flat spin, again.

What version of the product are you using? On what operating system?
Tricopter, APM 2.6, Arducopter V3.0.1, FW V: 120, Win 7, 64 bit.

Additional notes:
1.  I understand that I can reverse channel 4 in mission planner to correct the 
rudder reversal. Don’t know if this is correct.

Original issue reported on code.google.com by lesliene...@gmail.com on 2 Nov 2013 at 10:16

[GoogleCodeExporter]

Follow-up. My tricopter is an RC Explorer build. After dropping the yaw rate P 
value down to a ridiculous 0.0200 and the RateRoll/RatePitch down to 0.800, it 
still immediately goes into a flat spin as soon as it clears the ground. 

Tricopters seem to be the Ardu orphans. I don't find many solutions to 
tricopter PID problems on the forums. Starting to wonder if APM 2.5 or 2.6 is 
made for tricopters. I would like to hear directly from the 3DR people on this 
issue.

Original comment by lesliene...@gmail.com on 5 Nov 2013 at 12:20