ArduCopter Release Notes:
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ArduCopter 3.0.0-rc1 01-May-2013
Improvements over 2.9.1b:
1) Inertial navigation for X & Y axis (Randy/Leonard/Jonathan)
2) 3D waypoint navigation library (Leonard/Randy)
    WPNAV_SPEED, WPNAV_SPEED_UP, WPNAV_SPEED_DN control target speeds during missions and RTL
    WP_YAW_BEHAVIOR to allow disabling yaw during missions and RTL
3) PX4 support (some features still not available) (Tridge/Pat/PX4Dev Team)
4) Safety improvements:
    Tin-can shaped fence (set FENCE_ENABLED to 1 and copter will RTL if alt > 150m or horizontal distance from home > 300m) (Randy/Tridge/Leonard)
    GCS failsafe (set FS_GCS_ENABLED to 1 and if you are using a tablet to fly your copter it will RTL and return control to the radio 3 seconds after losing telemetry) (Randy)
    pre-arm checks to ensure accelerometer and radio calibration has been performed before arming (Randy)
5) motor interference compensation for compass (Jonathan/Randy)
6) Circle mode improvements:
    set CIRCLE_RADIUS to zero to do panorama shots in circle mode (copter does not move in a circle but instead slowly rotates)
    CIRCLE_RATE parameter allows controlling direction and speed of rotation in CIRCLE mode and LOITER_TURNS (can also be adjusted in flight from CH6 knob)
7) SONAR_GAIN parameter add to allow reducing the response to objects sensed by sonar (Randy)
8) support for trapezoidal quads (aka V shaped or FPV quads) (Leonard/Craig)
9) performance improvements to dataflash logging (Tridge)
10) bug-fix to analog read which could cause bad sonar reads when using voltage or current monitor (Tridge)
11) bug-fix to motors going to minimum when throttle is low while switching into Loiter, AUTO, RTL, ALT_HOLD (Jason/Randy)
12) bug-fix for auto disarm sometimes disarming shortly after arming (Jason/SirAlex)
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ArduCopter 2.9.1b 30-Feb-2013
Improvements over 2.9.1:
1) reduce INS_MPU6K_FILTER to 20hz
2) reduce InertialNav Z-axis time constant to 5 (was 7)
3) increased max InertialNav accel correction to 3 m/s (was 1m/s)
4) bug fix for alt_hold being passed as int16_t to get_throttle_althold_with_slew
5) bug fix for throttle after acro flip (was being kept at min throttle if pilot switched out of ACRO mode while inverted)
6) reduce yaw_rate P default to 0.20 (was 0.25)
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ArduCopter 2.9.1 & 2.9.1-rc2 01-Feb-2013
Improvements over 2.9.1-rc1:
1) small corretion to use of THR_MID to scale lower end of manual throttle between THR_MIN and 500 instead of 0 and 500
2) bug fix for longitude scaling being incorrectly calculated using Next Waypoint instead of home which could lead to scaling being 1
3) ESC calibration change to set update rate to ESCs to 50hz to allow simonk ESC to be calibrated
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ArduCopter 2.9.1-rc1 31-Jan-2013
Improvements over 2.9:
1) THR_MID parameter added to allow users to adjust the manual throttle so that vehicle hovers at about mid stick
2) bug fix for autotrim - roll axis was backwards
3) bug fix to set sonar_alt_health to zero when sonar is disabled
4) capture level roll and pitch trims as part of accel calibration
5) bug fix to ppm encoder false positives
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ArduCopter 2.9 & 2.9-rc5 14-Jan-2013
Improvements over 2.9-rc4:
1) add constraint to loiter commanded roll and pitch angles
2) relax altitude requirement for take-off command to complete
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ArduCopter 2.9-rc4 12-Jan-2013
Improvements over 2.9-rc3:
1) Smoother transition between manual and auto flight modes (Leonard)
2) bug fix for LAND not actually landing when initiated from failsafe (Randy/Craig)
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ArduCopter 2.9-rc3 11-Jan-2013
Improvements over 2.9-rc2:
1) alt hold with sonar improvements - now on by default (Leonard/Randy)
2) performance and memory useage improvements (Tridge/Randy)
3) increase APM1 baro pressure read from 5hz to 8.3hz to improve alt hold (Randy)
4) bug fix: altitude error reported to GCS (Randy)
5) limit inertial nav's max accel offset correction to 100cm/s/s to speed up recovery after hard impacts (Randy)_
6) moved rate controllers to run after ins read (Tridge/Randy)
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ArduCopter 2.9-rc2 31-Dec-2012
Improvements over 2.9-rc1:
1) increased throttle rate gains from 1.0 to 6.0
2) APM1 fix so it works with inertial nav (5hz update rate of baro was beyond the tolerance set in the inav library)
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ArduCopter 2.9-rc1 23-Dec-2012
Improvements over 2.8.1:
1) altitude hold improvements:
    a)inertial navigation for vertical axis [Randy/Jonathan/Leonard/Jason]
    b)accel based throttle controller [Leonard/Randy]
    c)accelerometer calibration routine updated to use gauss-newton method [Randy/Tridge/Rolfe Schmidt]
    d)parameters to control climb rate:
        AUTO_VELZ_MIN, AUTO_VELZ_MAX - allows you to control the maximum climb and descent rates of the autopilot (in cm/s)
        PILOT_VELZ_MAX - allows you to control the maximum climb/descent rate when in alt hold or loiter (in cm/s)
2) landing improvements [Leonard/Randy]
    LAND_SPEED - allows you to set the landing speed in cm/s
3) camera related improvements:
    a) AP_Relay enabled for APM2 and integrated with AP_Camera [Sandro Benigno]
    b) camera trigger with channel 7 switch or DO_DIGICAM_CONTROL mission command [Randy]
    c) allow yaw override by pilot or with CONDITIONAL_YAW command during missions [Randy]
        YAW_OVR_BEHAVE - Controls when autopilot takes back normal control of yaw after pilot overrides (0=after next wp, 1=never)
4) trad heli improvements [Rob]
    a) code tested and brought back into the fold (2.8.1 was never released for trad helis)
    b) enabled rate controller (previously only used angle controllers)
    c) fix to rotor speed controllers - now operates by switching off channel 8
    d) allow wider collective pitch range in acro and alt hold modes vs stabilize mode
    e) removed angle boost function because it created more problems than it solved
    f) bug fix to allow collective pitch to use the entire range of servos
5) mediatek gps driver improvements [Craig]
    a) added support for 1.9 firmware
    b) bug fix to start-up routine so sbas can be enabled
6) failsafe improvements (both throttle and battery) [Randy/Craig/John Arne Birkeland]
    a) RTL will not trigger if your throttle is zero - reduces risk of accidentally invoking RTL if you switch off your receiver before disarming
    b) failsafe triggered in unlikely case of a PPM encoder failure
    c) bug fix to resolve motors momentarily reducing to zero after failsafe is triggered
7) mpu6k filtering made configurable and default changed to 42hz for copters [Leonard/Tridge]
8) support ppm sum for transmitters with as few as 5 channels [Randy/John Arne Birkeland]
9) acro trainer - copter will return to be generally upright if you release the sticks in acro mode [Leonard]
    ACRO_BAL_ROLL, ACRO_BAL_PITCH - controls rate at which roll returns to level
    ACRO_TRAINER - 1 to enable the auto-bring-upright feature
10) other changes and bug fixes:
    a) allow >45 degrees when in stabilize mode by adding lines like below to APM_Config (compile time option only) [Jason]
        #define MAX_INPUT_ROLL_ANGLE 6000     // 60 degrees
        #define MAX_INPUT_PITCH_ANGLE 6000    // 60 degrees
    b) bug fix to stop RTL from ever climbing to an unreasonable height (i.e. >80m) [Jason]
    c) event and state logging [Jason]
    d) allow cli to be used over telemetry link [Tridge]
    e) bug fix to allow compass accumulate to run when we have spare cpu cycles [Randy]
    f) bug fix so do_set_servo command works [Randy]
    g) bug fix to PID controller's so they don't calculate crazy D term on the first call [Tridge]
    h) bug fix to initialise navigation parameter to resolve twitch when entering some navigation modes [Jason]
    i) performance improvement to copter leds - use DigitalFastWrite and DigitalFastRead instead of native arduino functions  [Randy]
    j) removed unused stab_d from roll and pitch controller [Jason]
    k) bug fix for guided mode not reaching target altitude if it reaches horizontal target first [Randy]
    l) code clean-up, parameter documentation improvements [Randy/Jason/Rob/others]

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ArduCopter 2.8.1 22-Oct-2012
Improvements over 2.8:
- 430 bytes of RAM freed up to resolve APM1 level issue and reduce chance of memory corruption on both APM1 and APM2

Improvements over 2.7.3:
- Improved ACRO mode (Leonard Hall)
- Improved stability patch to reduce "climb-on-yaw" problem (Leonard, Rob Lefebvre, Randy)
- Rate controller targets moved to body frames (yaw control now works properly when copter is inverted) (Leonard/Randy)
- Less bouncy Stabilize yaw control (Leonard)
- OpticalFlow sensor support for APM2.5 (Randy)
- DMP works again by adding "#define DMP_ENABLED ENABLED" to APM_Config.h You can also log DMP vs DCM to the dataflash by adding "#define SECONDARY_DMP_ENABLED ENABLED" (Randy)
- Watch dog added to shutdown motors if main loop feezes for 2 seconds (Randy)
- Thrust curve added to linearize pwm->thrust. Removes deadzone found above 90% throttle in most ESC/motors (Randy)
- More timing improvements (main loop is now tied to MPU6000s interrupt) (Randy)
- GPS NMEA bug fix (Alexey Kozin)
- Logging improvements (log I terms, dump all settings at head of dataflash log) (Jason)

Bug Fixes / Parameter changes:
- fixed skipping of last waypoint (Jason)
- resolved twitching when no GPS attached (Tridge)
- fixed loss of altitude if alt hold is engaged before first GPS lock (Randy/Jason)
- moved Roll-Pitch I terms from Stabilize controllers to Rate controllers
- TILT_COMPENSATION param tuned for TradHeli (Rob)

Code Cleanup:
- HAL changes for platform portability (Pat Hickey)
- Removed INSTANT_PWM (Randy)
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