Rebased Ackerman vehicle controllers

[marcozorzi]

This is a rebased and squashed version of #7139

[dagar]

I think this PR has gotten away with it so far, but one thing I'll need to look at before it's mergable is the vehicle type reported by vehicle_status (commander) and any module checking it.
Some parts of the code assume the vehicle is a FW if vehicle_status.is_rotary_wing == false.

[marcozorzi]

Yes, agreed. While coding I was thinking that there could be a new vehicle status, which could be wheeled, ackerman or something else but I thought that would result in refactoring other apps.

[marcozorzi]

@dagar this is unused, can we remove it? I also have a commit ready to fix the coding style, this should fix the checks issues once and for all

[TSC21]

To help on passing on travis:
https://travis-ci.org/PX4/Firmware/jobs/229043348#L416 (remove this, since it is not used)

https://travis-ci.org/PX4/Firmware/jobs/229043344#L414 (run make format and fix style)

circleci:
https://circleci.com/gh/PX4/Firmware/5223?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-build-link (same error about unused variable as #L416)

[marcozorzi]

Thanks @TSC21, this should do it.

[TSC21]

Just picking up what I said in the other PR:
Also please add some documentation about this on https://dev.px4.io/. Create a subsection in https://dev.px4.io/en/airframes_experimental/ with the name "UGV/ROVER" or something like that (you can rename this same section to "UGV/Rover" only instead of "Boats, Submarines, Blimps, Rovers" so to be more specific), add a part list to build a RC car like yours (Traxxas Stampede VXL), an assembly guide, a general schematic of the different parts and how they are connected, the servo connections schematic, a list of mixers values and the PID tunning you used, and finally add some photos. Add everything you think it can be useful and informative.
This would help others that would like to build a UGV like yours or something similar.

[marcozorzi]

Ops, I guess this last message got lost in the final rush of my thesis. Sorry about that. I am planning on doing the guide as soon as possible, I'll keep you posted.

[dagar]

I'm still very interested in this. As soon as v1.6.0 is released let's do a final pass to get this in a mergeable state and get it in.

[marcozorzi]

As per the message above, I was finally able to create the Devguide page for this. @TSC21 let me know what you think!

[LorenzMeier]

@dagar Can you have a pass? It looked good for me.

[TSC21]

@marcozorzi thanks for the add for the Devguide! This is ok to me as is also. We can work forward on developing the modes and control to make them more independent from the fw logic.

[TSC21]

@marcozorzi after this is meged you can update PX4/PX4-Devguide#169 so it points to the main repo instead of your repo.

[dagar]

I'll go through this again tomorrow, but it should be good to merge.

[dagar]

Merging!

[TSC21]

@marcozorzi and @dagar maybe we can schedule a call on how we can structure this to be more independent of fw code and also improve "flight" modes?

[marcozorzi]

Awesome!! I'm up for a call, thanks for the great help!

[dagar]

I'm up for it if you have specific ideas to discuss. I view this as just the start.
We can create a new UGV tag for the repo and a project board (https://github.com/PX4/Firmware/projects) if necessary.

As for the modes the first step is generalizing the FW, MC, VTOL vehicle_status flags and then in the state machine we can block modes that don't make sense for cars (ie altitude, takeoff, landing).

I'm personally interested in expanding the manual modes which we could probably get away with calling 'acro', 'stabilized', etc. Speaking for my own terrible driving I think having some kind of crude traction control or even throttle slew rate would be helpful. I suppose manual input (stick or wheel?) would simply be a yaw rate command and possibly lock on to the current heading if input is neutral?

[marcozorzi]

Sounds good to me!