Rover: Add RTL_ENABLE parameter

[yuri-rage]

Feature request

Request an RTL_ENABLE parameter for Rover that will allow users to opt out of all RTL behaviors by setting this parameter to zero.

Is your feature request related to a problem? Please describe.

Large, land-based vehicles rarely if ever have a valid use case for RTL.

Recently, a user had a large mower accidentally activate RTL mode, which could have been catastrophic. Making a beeline for home could have dire effects if RTL is accidentally activated (either by failsafe, mission command, or errant mode change). Of course, this is all user error related, but if a vehicle should never be able to enter RTL, there should be a way to signal that to the autopilot and prevent such error from ever occurring.

Describe the solution you'd like

Parameter as described in opening statement.

Describe alternatives you've considered

I have written a Lua script to detect errant RTL activation and immediately switch to HOLD mode. However, this is only valid for scripting enabled autopilots, so it is not a universal solution.

Platform [ ] All [ ] AntennaTracker [ ] Copter [ ] Plane [x ] Rover [ ] Submarine

Additional context

Relevant Discord discussion with @rmackay9: https://discord.com/channels/674039678562861068/797946854792757259/1245931364134551552

Relevant Mission Planner issue discussing the method by which the user accidentally stumbled into RTL: https://github.com/ArduPilot/MissionPlanner/issues/3358

[IamPete1]

We do have FLTMODE_GCSBLOCK, it does have a RTL bit. That would prevent switching to RTL from the GCS. Of course there are still failsafes...

[yuri-rage]

We do have FLTMODE_GCSBLOCK, it does have a RTL bit. That would prevent switching to RTL from the GCS. Of course there are still failsafes...

Would not prevent an RTL from auto, which was the root cause here. Other suggestions include proper use of inclusion/exclusion fences. I understand we can't save everyone from themselves, but an opt-in feature like this might well be of value.

[muramura]

Without preparing a new flag, I think it can be set to each failsafe action.

I think SMART RTL is better than RTL. SMART RTL determines the shortest return path based on the travel history. It doesn't return in a straight line like RTL.

https://ardupilot.org/rover/docs/rover-failsafes.html#failsafes

[yuri-rage]

Without preparing a new flag, I think it can be set to each failsafe action.

I think SMART RTL is better than RTL. SMART RTL determines the shortest return path based on the travel history. It doesn't return in a straight line like RTL.

https://ardupilot.org/rover/docs/rover-failsafes.html#failsafes

Correct on both counts, however...

Failsafe actions will not preclude accidental entry to RTL via an errantly applied RTL waypoint during an auto mission (which is really the intent of the feature request). And SRTL still has many pitfalls and a lack of application on the vehicles in question. For example, but not limited to: SRTL memory fills during prolonged missions and subsequently fails.

Moreover, I would almost always recommend against the use of SRTL on large land vehicles. The path, while deterministic, is not readily apparent to the user, making it appear as non-deterministic behavior, and I would NOT want a large vehicle wandering home via a path I have to assume is valid (or potentially retracing many spiral path waypoints before an assumed valid path direct to home can be achieved).

Most of the users with whom I'm familiar either plan the mission to end at a specific, predetermined point or simply let the vehicle enter hold mode in the middle (or edge) of a field at the conclusion of a grid/spiral path, awaiting a manual drive to the next area of interest or back to storage. One even has a script that detects mission complete, waits some period of time for user interaction, and then simply shuts the engine down. None use RTL or SRTL for all of the reasons already stated. Some could admittedly make better use of exclusion fences, but I'm not sure that makes a successful case for ignoring the feature request.

[geofrancis]

I drive my rovers around town, if it ever tried to RTL it would either end up on the road or into a wall so I would enable this if it was an option.

[IamPete1]

I don't think RTL is the default action for any of the failsafe', they either report only or go into hold. We can protect against accidental switch from the GCS with FLTMODE_GCSBLOCK.

So the user has to setup a RC switch or configured a failsafe action to RTL.

Preventing entering RTL from a mission command could not be enabled by default, because that would break existing setups. So it would only save people after the first crash when they go and read about how they could have prevent it.

A lua script to add a pre-arm for RTL points in the mission would be quite straight forward. (or the very simple script suggested in the issue)

Fence and avoidance sensors might prevent the crash if not the RTL itself.

[yuri-rage]

Preventing entering RTL from a mission command could not be enabled by default

Agree. My suggestion is an RTL_ENABLE parameter with 1 as the default value, such that it would not be a breaking change.