Build the BEST Ardupilot Crop Sprayer

As the title says, i’m planning to build the best ardupilot crop sprayer, for this, I need help to put everything I want together and make sure that will work as it should.

Why I want? As everyone knows, DJI has the best crop sprayers and its a very closed company, its hard to buy replacement parts, add features to FC and get support. We have a perfect FC (pixhawk cube) and crop sprayer is a thing that our FC still has trouble, this article is a research for a future build that i’m planning to do and I will share with everyone here step by step how to build one.

What am I planning?
I want to build a crop sprayer, fully autonomous, with lidar to control height, realsense depth camera for object avoidance and path planning if any obstacle found. It has to work with full autonomous mode.

Let’s split in parts:

1-Frame:
The frame must be a very rigid stratucture to hold everything, I have experience in frame building for heavy lift. No questions here.

2-Main Eletronics:
It will use pixhawk cube, here 3 with rtk, rfd900x telemetry, PDB and etc…
-Question: Can I use dual here 3 with rtk for redundancy?

3-Realsense depth camera and path planning:
For make this work I have to use a onboard pc as RPi as says in this article: https://discuss.ardupilot.org/t/gsoc-2020-integration-of-ardupilot-and-realsense-d4xx-depth-camera-for-simple-obstacle-avoidance/58474
The hardware implementation is very detailed, but is doesn’t explain how to make it work with BendyRuler path planning.
-Question: As I can Bendyruler path planning in auto mode, can I use the depth camera for object avoidance together autonomous path planning.
*I Must use it becouse it may has a object in the field and I want the copter autonomous avoid it and continue with the mission.

4-ZigZag Mode:
This mode its very useful for a crop sprayer, as it says on documentation: https://ardupilot.org/copter/docs/zigzag-mode.html, after version 4.1.0 will be implemented a automatic zigzag mode, but the point A and B has to be marked flying to those points.
-Question: It will be much more reliable if I can draw a polygon around the area previously at MP and the upload to copter and start zigzag mode, can I do that?
-Another question is, if it has a failsafe (battery or low pesticide in tank), this mode will save the last point, return to home and after clear the failsafe, return to last saved point (without lua scripts)?

5-Sprayer System:
In this link: https://ardupilot.org/copter/docs/sprayer.html#sprayer, explain how to set up the pump, to maintain a constant sprayer rate, the pump will increase linearly 10% of each 1m/s of speed, this way will maintain constant sprayer rate.
-Question: Is it possible to use a flowmeter and regulate it a fixed value? this way the pump will increase or reduce as flowmeter reads the flow rate. Its open a new variable, the possibility to set the rate needed without changing sprayer nozzle.

6-Map after operation:
This part is a suggestion. After finish the work, it will be very useful is the FC paints in another color where the copter was. Let me explain, the copter will cover for exemple 1 meter of spraying area, in the screen of mission planner, it should paint this one meter in the line of the copter.

It will be very helpful if everyone help answering those questions for later we build the best ardupilot copter sprayer.

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