Spaying accuracy is one of the most important reasons that the fully automatic drones are not widely used in the pesticide spraying application. The accuracy is mainly constraint by the GPS positioning accuracy.

 

But what about using DGPS (not mean SBAS) in this application? It may cost around 10000 USD but I guess most of the users may be able to afford it. And fully automatic drone with DGPS will be able to spray pesticide more accurately than manually controlled drone.

Why DGPS is still not widely used in this area? What are the reasons?

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I believe that more of a problem will be carrying the water (+chemical/s), more than mounting/utilizing a DGPS. 

In Japan they use Yamaha´s RMAX for spraying.

I don't get your point. Do you mean the problem is more about c.g. range due to the liquid movement and load? It is a critical problem but I guess it is the same for non/half automatic drone and fully automatic drone. I don't get how could this problem block the fully automatic control and navigation application in pesticide spaying area.

talking about the payload. It will all depend on much area you want to spray, which volume of water per unit of area, and how much weight can your drone carry.

Make your math and you´ll probably see that you´ll need a large drone to cover a  small area.

My point is that I don´t see what would be the advantage of a drone over an airplane, for spraying purposes? talking of commercial fields in extensive crops.

If they were very small fields, or experimental plots, that´s a different story.

I agreed with Jose.
The problem is the payload.
Check the sprayers market. A 200 liters sprayer is a very small one. I work selling Agricultural equipment and all the clients uses sprayer from 600 to 6000 liters.
Tha is the limitation for me, and when you talk about spraying with accuracy aerial vehicles are not a good option. usually you look for no wind and the nozzle as low as you can.

Yes. Pesticide spraying drones can not compete with manned airplane for large farmland. I guess most of the purchasers of the pesticide spraying drones only use them for very small field, or experimental plots. 

 

Let me ask about these drone purchasers story. These small land (or experimental plots) owner will also want their drones to be able to fly and spray fully automatically over their small land, so that the drone spraying operation work load can be greatly saved. In these case, DGPS will be needed to help on having acceptable accuracy.

with no intention of being negative, just digging into the challenges of this interesting topic: there is one point to consider: drift management. Regardless of the precision of the GPS, who will make the decision of how to manage the drift (of the applied product)? In the case of airplanes, the pilot does the job. Some pesticides would travel miles on the air under certain conditions, it´s a fact, you wouldn´t want to spray your neighbour´s field...

I understand Yamaha´s RMax s are used in Japan for spraying purposes, I am curious how they do it.

The drones fly only 2-5 meters above the crops and the there's strong downwash from the rotor. The pesticide won't drift away normally. So for fully automatic flight, the GPS precision will be essential.

The payload is indeed the biggest issue here, I am wondering what's the biggest payload possible, I have managed to get 125kg flying time about 35 min

Ok guys, here is the deal. Not all UAV applications can be performed by 1 kind of drone.

Look at this like an engineer,

1) Site the demands of the application, range, payload, flight time, precision

2) Identify methods of meeting the demands - different size multi rotors, different size airplanes.

3) Choose the best configuration and work to make that option work with your personal constraints.

I never quite understood why people would spray an open field with a multi-rotor, they are a precision flying instrument, not a work horse. Even with solid applied physics( high voltage motors, high density batteries, light weight components) the efficiency and payload capacity of multi rotor is very low.

Airplanes on the other hand are the work horse that is ideal for this application. UAV airplanes can fly closer to the ground than manned aircraft reducing drift in windy conditions. UAVs can service smaller fields where manned airfraft cannot get to. In summary, the expense of flying a payload of pesticide with an airplane is much much lower than a multi rotor. Adding good optical and sonic altitude sensors will the craft skim very close to the ground safely.

The draw back is that your ability to pilot the plane for take-off and landing is important.

Yes there are auto take-of and auto Land features that are part of mission planner, however, this plane has a sprayer on the bottom which needs to be protected from damage and leaving the dangerous parts of the flight ( take off and landing) is not a good idea in my opinion.

If anyone needs design advice or a quote for a custom built Multi Rotor or Airplane, plz visit my website.

www.Aerosurveysolutions.com

DGPS should become the new standard in my opinion. Hopefully with the growing UAV industry they will be cheaper soon.

I dont know why everyone is ok using the low power, singe antenna telemetry to fly their drones, the range and quality just isnt there and you would loose your drone over the slightest signal interference or obstruction.

I have been looking for an affordable DGPS system that is designed for a drone but I have not found a pairing yet that will do the trick.

I did find a 1cm accurate GPS system that has 2 sides (air and ground) but the retail price is $900....

I have been using the Ublox M8N, which holds perfectly still in Position Hold. I do not see much drift in the flight path if any.

The main issue I see with GPS right now s reliability and 'True Accuracy.'  My GPS will hold the craft pefectly still but the exact accuracy of the GPS is not as strong as I'd like it to be.

If you have a link for a reasonably priced DGPS plz post a link

1 cm accurate GPS....900 USD

Could you provide the link of it?

M8N is not the 'real' DGPS. It doesn't have the ground station by itself. Theoretically, it is not that accurate in countries without public ground station, e.g. China. 

Agreed, I was trying to say that the M8N is good for flying but probably not sufficient for mapping.

I will send the link soon, my business partner researched that particular unit.

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