Copter-3.4-rc1 has been released for beta testing and can be downloaded using the Mission Planner's Install Firmware screen's beta firmware link. Some of the changes since Copter-3.3.3 are listed below.
1) EKF2 allows "boat mode" (attitude initialisation without gyro calibration)
2) Throw mode by Paul Riseborough
3) Terrain following:
a) Support terrain altitudes during missions using GCS's map data or rangefinder (i.e. Lidar)
b) LightWare range finder driver fixes (I2C works but we still recommend using Serial interface)
c) Bebop sonar support (we strongly recommend the Bebop2 over the original Bebop)
4) Precision Landing using IRLock sensor
5) Attitude controller re-organisation (all parameter changes automatically moved and scales adjusted)
a) RATE_ parameters become ATC_RAT_ (i.e. RATE_RLL_P becomes ATC_RAT_RLL_P)
b) Rate Roll, Pitch, Yaw P, D are reduced by 10% for X, V, H frames, increased by 27% for all other frames
c) STB_ parameters becomes ATC_ANG_ (i.e. STB_RLL_P becomes ATC_ANG_RLL_P)
6) Motors library improvements:
a) support OneShot ESCs (set MOT_PWM_TYPE to 0 for Normal, 1 for OneShot or 2 for OneShot125)
b) TriCopter compensates for tail servo angle
c) SingleCopter, CoaxCopter adjust control surfaces based on throttle output
d) MOT_PWM_MIN, MAX allow specifying output ranges to ESCs which are difference from throttle input channel (i.e. RC3)
e) TradHeli servo objects moved into heli class (HSV_ parameters become H_SV1_)
7) uAvionix Ping sensor support (ADS-B vehicles appear on GCS, avoidance will come in future release)
8) Improved Solo support (gimbal and buttons now work)
9) Pixracer support
a) warning if GPS update rate is slow (under 5hz, does not stop arming)
b) RTL cone (vehicle won't climb to the full RTL_ALT if it is RTL-ing from close to home)
Warning: It has been reported that Tower's Follow-Me mode causes a rapid descent with Copter-3.4 so we recommend not using Follow-Me until this is resolved (it's likely a mix-up as we've added support for absolute and terrain altitudes).
For this release we will be doing the support on the new ArduPilot discourse server instead of creating a monster thread here on DIYDrones.
Thanks in advance to the beta testers!
P.S. I would like to personally thank EnRoute (youtube channel) for stepping in to support my ongoing development efforts on ArduPilot and Colestl/GatewayGeospatial for their sponsorship of the Terrain following work.