How to Kill Weeds on Your Roof With a Drone

About: Inventor and Emergency Doctor.

I was very disappointed to spot a plant growing out of my chimney. This was particularly as it is inaccessible without scaffolding and the house had only been scaffolded only a few weeks previously in order to repair the fascia boards. Unfortunately, we did not notice the plant until after the scaffolding came down; I was concerned that if we left it then rainwater would be able to enter the chimney and would cause water damage to the bedroom underneath. Even with a tower and a roofing ladder builders and roofers have been reluctant to go up as far as the ridge as if they fell there is a long drop to the ground without scaffolding.

I realised a great solution would be to deliver some weedkiller directly onto the plant using a drone. I Googled it and nobody is currently doing this, which I found surprising.

I was determined not to be beaten and saw this as a great excuse to buy a drone. I had wanted a drone for some years but had never been able to justify buying one until now!

Supplies:

Drone

Weedkiller

Stiff wire

Old pen barrel

Small fragment of mirror (get someone else to break it so they get 7 years bad luck instead of you). You won't need this if your drone

Gaffer tape

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Step 1: Controlled Delivery of Weedkiller

I did not want to invest in a complicated drone and did not want to spend more than about £70. After some consideration I settled on this one from Holystone on Amazon; https://amzn.to/2nSI9AO. It's a great drone, easy to fly and even folds to go in your pocket.

It didn't have a spare RC channel to control a delivery system as these drones only have basic controls. This also meant that the system would need to have a controlled release of weedkiller. After trying a small layer of ice in the base of the pen lid I decided that just having a tiny hole so that it would take a minute or two for the weedkiller to drip through would be the most effective option.

Step 2: Get Some Practice With Your Drone

The flying conditions when trying to deliver the weedkiller using a drone can be rather tricky. You will need to be near the building or whatever it is that you are trying to get the weed killer onto which I found causes two problems. Firstly, there is the collision risk, secondly there can be sudden changes in airflow. As the weed on our roof was near the apex I found that air seemed to rise up one side and down the other making it difficult for me to keep the drone stable. It is not recommended to fly near buildings so make sure you are confident about your ability!

Make sure you get plenty of practice in. Get used to flying the drone accurately and in close proximity to walls, trees and other obstacles.

Step 3: Drone Modifications

Being a relatively inexpensive drone the camera only pointed forwards, where as I wanted to be able to see straight down. I got a tiny shard of mirror and taped it in front of the camera at 45 degrees. This worked surprisingly well. if you have a drone whose camera can be pointed downwards then you will not need to do this step.

Step 4: Make a Hole in the Bottom

Make a tiny hole in the bottom, as small as you can. You can test how long it lasts for by filling the pen lid with water and seeing how it takes to empty. This will give you an idea of how long you have got to get the drone in position and how long you need to keep it there.

Step 5: Weedkiller Delivery System

Use the body of a pen or similar receptacle for the weedkiller storage and delivery. Depending on the size of your drone you may get away with a larger quantity. My first attempt used thread to attach the pen to the drone but it span and whirled wildly in the downdraft from the drone's rotors. I switched to using stiff wire instead which gave much better control. Stabilising it made the drone easier to control as well.

Step 6: Attach the Wire

Attach about 2 feet of thick stiff wire to the pen body. Drill a hole through both sides, push the wire through and twist it. Twist the other end of the wire onto the drone's landing gear.

Step 7: Taking Off

Your drone now has a a couple of feet of stiff wire sticking out from the bottom of it; this makes taking off and landing rather tricky. Place two plant pots or similar raised platforms a few inches apart so that the drone can perch across these with the wire pointing downwards. I managed to balance the drone on the edge of a box. This allows you to take off and land without the wire hitting the ground and tipping the drone.

Take off and hover drone about 6 feet in the air so that you can fill the pen with weedkiller. You can see me do this in the video. Quickly grab the controller and get the drone in position as soon as possible. Try to hover directly over the plant so that the drips of weedkiller land squarely on it. Remember you can have as many goes as you like and can do some practice runs if you need to.

Step 8: An Alternative Method

For a second application I used my larger drone and suspended a polythene freezer bag underneath. This had the advantage of delivering a larger amount of weedkiller. Suspend the bag from three or four points to stop it spinning and swaying as this will destabilise the drone. The harness shown worked well although the drone was a bit bottom-heavy.

Check your freezer bag for holes before putting about 50mls of strong weedkiller in it and tying the top with as much air in it as you can. This makes it easier to pressurise and makes sure all the weedkiller runs out. Put a rubber band around the bag to pressurise it, take off, hover at head height then make a hole in the bottom with a pin before flying up onto the roof. I mounted a pin pointing upwards in some Blu-Tac on the floor which I flew the drone down onto before flying up to the roof. This minimised the time between puncturing the bag and reaching the roof.

Let me know any improvements/ideas and please post photos of your weedkilling attempts in the comments!

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