lothman said:
Here something I wrote elsewhere on Course Lock and Home Lock that might be of some interest.
Note the following is consistent with current NAZA firmware/documentation (v 3.16, 2013-08-07) and I think with more recent prior versions as well. Also assumes Mode 2 transmitter setup (ie rudder and throttle on left stick). Note also that the IOC switch by default is not active on a Phantom. You must run DJI's Assistant software to activate IOC function.
In normal flight mode (IOC Switch = Off), the craft's flight response to the right stick ('left/right and forward/back') is relative to the current orientation of the craft. So moving the right stick forward sends the craft in the direction the craft's nose is pointing.
Course Lock (CL) behavior is based upon the craft's previously recorded reference orientation (I'll call this the 'Home Orientation'). The Home Orientation is initially based on the craft's orientation 30 sec after the NAZA is powered up. The Home Orientation can also be set manually by toggling the IOC switch from Off to Course Lock, and back to Off quickly 3 to 5 times.
When flying in CL Mode (IOC Switch = CL), craft response to the right stick ('left/right and forward/back') is relative to the previously recorded Home Orientation, and NOT based upon the craft's current orientation. This remains true no matter where the craft is relative to the Home Point (assuming a Home Point has actually be established) and no matter which direction its nose is pointing. Thus CL flight behavior depends only upon the NAZA knowing the craft's current orientation relative to the Home Orientation in order to figure out how the craft should respond to inputs from the transmitter. This information does not rely on any inputs from the GPS system, therefore CL Mode can be used in both 'ATTI' Mode and 'GPS ATTI' Mode (CL mode will not function Control Mode is set to Manual). And CL Mode does not require GPS satellite acquisition or establishing a Home Point.
Home Lock (HL) behavior is based upon the craft's location 'at the moment' relative to the previously recorded craft location (the 'Home Point') usually established before takeoff as the position of the aircraft when you start the motors for the first time after 6 or more GPS satellites have been found for 10 seconds. The Home Point can also be set manually by toggling the IOC switch from Course Lock to Home Lock, and back to Course Lock quickly 3 to 5 times.
When flying in Home Lock Mode (IOC Switch = HL), craft response to the right stick is relative to the vector (arrow) pointing from the Home Point (usually established prior to take-off) toward the craft's current location (determined via GPS data). No matter where the craft is (provided its at least 10 m from the Home Point) and no matter which way the craft's nose is actually pointing, the tip of this vector represents the craft's virtual nose in HL flight and the craft's responses reflect this fact. Moving the right stick forward causes the craft to fly 'out' (away from the Home Point) along the straight line between the Home Point and the craft's current position. Pulling the right stick back causes the craft to fly 'in' (toward the Home Point) along the straight line between the Home Point and the craft's current position.
Clearly, HL flight requires GPS data (6 or more GPS satellites) both to establish the Home Point and to allow the vector from Home Point to the craft's current location to be determined. HL Mode flight also requires that the craft is at least 10 m from the Home Point, a criterion that can only be calculated with GPS information. When the craft is <10 m from the Home Point, then its flight behavior automatically reverts to Course Lock Mode behavior. Given this dependency on GPS data, it makes sense that HL mode can only be realized when at least six GPS satellites are found and the Control Mode is set to 'GPS ATTI'.
The key here is the distinction is between craft orientation (which way is the nose pointing) vs. craft position (where in 3D space is the craft located). CL Mode relies on orientation information while HL Mode uses both position (GPS) and orientation (compass, gyro, accelerometers).
I would strongly encourage those interested in using these IOC modes to carefully read the DJI documentation and then to perform their own evaluations of fight behavior under controlled test conditions (rather than using IOC flight modes for the first time in an emergency or other critical flight situation). The documentation is helpful, but is not always entirely clear/correct so trust but verify...
Finally, I think the above is accurate, though certainly simplified. If it is inaccurate, unclear, or I've otherwise made some errors (certainly wouldn't be the first time!), pls advise.
Steve
