TradHeli - add TUNE for gyro gain

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Best performance is achieved by using an external gyro for yaw control.  To do 
this, we send a user specified gyro gain out on APM's output channel 7.  BTW 
this is set in the CLI by typing "setup", "gyro on <value" where <value> is the 
gyro gain which should be between 1000~2000.

It's slightly inconvenient for the user to figure out exactly what this gyro 
gain "value" should be:

1. connect my TX/RX channel 6 directly to the gyro gain, put my heli on a 
little rotating platform, start the the engines and adjusted the gyro gain 
manually until you find a gain that works.

2. reconnected TX/RX channel 6 back to the APM input channel 6 and ran the 
CLI's radio test to find out what value channel 6 was producing
used the CLI, setup, "gyro on <value>" to set the gyro gain to that value from 
the above two steps.

The need to mess about with the wiring would be removed if we set-up a TUNE 
value that directly sent the RX/TX's Channel 6 to APM's output channel 7.

Original issue reported on code.google.com by rmackay...@gmail.com on 9 Oct 2011 at 11:28

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[deleted comment]

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fixed!  Set TUNE to 13 via the AP_MissionPlanner and the external gyros's gain 
will be updated from your receiver's channel 6.

code change is tiny but you can see it here: 
http://code.google.com/p/ardupilot-mega/source/detail?r=350584cae42692675a0e21bc
c78b94fd0be9737a

also updated the wiki page

Original comment by rmackay...@gmail.com on 29 Oct 2011 at 12:24

• Changed state: Fixed