I am interested in a project where the drone (quadcopter) operates from a moving platform. This means taking off from, station-keeping, and landing on the moving platform. The home position would need to move with the platform/GCS. Think of a boat that is underway.
Does anyone have any thoughts on how to approach this? I feel like it would be a combination, of GPS, DGPS, “follow-me” mode, RTK-GPS? And perhaps some custom coding. The ultimate goal would be for the quadcopter to land on the moving platform autonomously. But, baby steps.
Having the GCS update the home position over mavlink is how it’s currently done. GCS applications such as Tower and the various 3DR Solo applications do this now. They read the GCS device’s GPS location (usually a phone or tablet) and use that to update the copter’s home location. I don’t believe mission planner currently does it.
However it is not a super robust method. RTL was never designed with this in mind, so there are some things to worry about:
RTL grabs the home position when it first begins, either by mode change or failsafe. So if you keep moving while the copter is doing an RTL, it is not going to account for that. It will land where the home position was at the time the RTL mode began. Your moving vehicle may already be 200ft away by then, and that is a problem that does not currently have a solution.
If the GCS stops sending the home position updates to the copter, then whatever the last position it got was will be be the home position. There is no means by which it will recognize “uh oh, my GCS stopped talking so this home position might be total BS now”.
The tower and solo apps store the old home position. So if the operator turns off the Return to Me function, the GCS changes the home position last time back to the real home position.
RTK GPS is probably not going to make any difference, mainly due to # 1 above. Custom code, either in ArduCopter or on a co-computer in guided mode, would be needed to make it continue to follow the moving base through the course of RTL and during the initial RTL descent. And a normal HERE (non-rtk) GPS would handle that just fine.
In reality, you would probably need to use the motor interlock or stabilize mode to touchdown safely and reliably in such a case. If it was a a grass hill, the automated landing might work. But if it is slick, moving, rocking, etc, stabilize or motor interlock will probably be needed.
