DJI RS2/RS3 should warn that RC yaw control does not support "follow"

[rmackay9]

As mentioned in this issue our DJI RS2/RS3 driver does not support RC yaw control in "follow" mode. RC yaw control is always "lock" mode (aka "earth frame").

We should add a warning to the DJI RS2/RS3 wiki page. Something like, "warning: Yaw rate control is always "follow" mode (aka "earth frame") meaning that if the user control the gimbal's yaw rotation rate from the RC (e.g. MNT1_RC_RATE > 0) the gimbal will rotate in "lock" mode (e.g. "earth frame", e.g. will not rotate with the vehicle). A work around is to always use yaw angle control (e.g. MNT1_RC_RATE = 0) or switch the mount to "Neutral" whenever the user wishes to re-center it.

This issue was identified in this Copter-4.5 discussion: https://discuss.ardupilot.org/t/ap-support-for-dji-rs2-rsc2-rs3-gimbals-maybe/91830/38

[Hwurzburg]

done

[rmackay9]

Thanks again!