PRE2018 4 Group3
|Han Wei Chia||1002684|
In the past few years beekeepers around the world have seen sudden dissapearances of wild and domesticated bees and a steady decline in the amount of honey bee colonies. According to research, causes of the observed decline can be found in the increase in pesticide use around the world and steadily increasing urbanization. Even climate change may be a factor that influences bee population decline.
Since around a third of the global food consumption depends on pollination by insects, of which the bee is a significant contributor, the decline or even extinction of these pollinators would have a large impact on our lives.
Besides proposed solutions to stop further decline of the bee population, there is a need to compensate the already occurred loss of pollinators. In this project, the intent is to research and design a replacement for bee pollination, in the form of a robotic and drone-like bee.
In this project our goal is to create a proof on concept of a drone that can collect pollen and subsequently pollinate flowers in a way that results in commercial quality produce. Furthermore we will give recommendations about the implementation of such a system of drones, focusing on the use of charging systems and noise reduction.
In order to reach our objectives, the following approach will be taken.
Firstly, a literature study will be done, focusing on the state of the art techniques that are currently being researched or developed in artificial pollination. Subsequently, research will be done into the important aspects of artificial pollination that are needed to design our drone. We will reach out to a stakeholder to discuss the requirements of an artificial pollinator, and in what way our product would be useful for the stakeholder.
When a significant part of the research is concluded, a model or proof of concept of the drone, with its collection and pollination devices will be made.
- Research about pollination
- Proof of concept of drone design
- Advice about e-hives and deployment
- This wiki
Our up-to-date planning can be found with the following link: .
Due to decreasing population of honey bees in recent years, there has been impacts in beekeeping industries as well as in the rate of pollination by bees. Because significant proportion of food consumption in the world depends on pollination by insects, those who provide materials for food processors definitely needs replacements for the future. Therefore, farmers and other food producers will profit from artificial pollination, as it allows them to continue their businesses. Farmers do not care whether their crops are pollinated by bees or artificially, as long as it does not affect their ways of farming too much. They will see artificial pollinators as a solution when the bee extinction starts to harm the global food production.
At this time, some beekeepers make a living by renting their bees to farms and municipalities that require more pollination. The jobs of those people will be complemented with robotic bees, so their job is saved, even if bees become extinct. Beekeepers will have to focus on repairing the robotic bee, rather than care for actual animals. If beekeepers can hande this shift in their business, they will not be affected by the robotic bee in a negative way. They do need to get used to not working with bees, as that was probably not just their business, but also their hobby. In that case, bee keepers can keep both ordinary bees and robotic bees, so their happiness is not affected.
There are more honey bees in this world than any other type of bee and pollinating insects. This means that honey bees are the most important pollinators of our food crops. Approximately one third of our food relies on the pollination by bees. Without honey bees, we would have a global food crisis that would kill a lot of people. This food shortage in case of an extinction will be prevented if an artificial pollinator replaces bees in time. The protection of our food chain is essential and vital to humanity's survival. Our global society as a whole profits from the replacement of bees.
Plants will be in trouble if pollinators die out. A lot of them would go extinct. This would lead to mass disruption of insect and wildlife life cycles. It would be hard to predict exactly what would happen, but there would be many negative impacts on user and society alike. There will be huge demand for other (artificial) pollination solutions. Robotic bees could be the solution and be very beneficial for enterprises to invest in, as they can rent their robotic bees to farmers, who can pollinate their crops. For the rest of the plants and trees, the government can either hire robotic bees from bee keepers or buy and maintain them on their own, perhaps as part of 'Staatsbosbeheer' or 'Rijkswaterstaat'.
As the world will need quite some of these drones, the producers of artificial pollinators will have a good business model with the production, marketing and selling of the drone pollinators.
We went to the Philips Fruittuin to explain our research and ask some questions about it and the bee probem. We spoke with the owner, Carlos Faes.
- What family of apples do you produce?
- All kinds of apples, different families of apples is good for the pollination
- Do you think the bees will be able to pollinate our food in the future?
- Yes, I think the bee problem will solve itself eventually. Nature has a way of fixing itself. If the bee population declines by half, people will have a food shortage and die out as well. This will give the bees room to grow again.
- People do not need to die if farmers become more artisan.
- People should have mutual respect for bees when dealing with them. Right now, their nectar is replaced with sober sugar water, which is not good enough for the bees.
- It is like with insects. In the chain of food productions, insects were a problem for the farmers, so people poisoned them. Because of this, a lot of farmers produce way more food, which also means the price dropped a lot, which makes it very hard for farmers to make some money. Once the farmers kick the bucket, there is going to be a food shortage in the world and people will die. This will result in a growth of insects again.
- If every farmer produces half of what they do now, everyone will be saved. But people are selfish and some farmers will still produce more (for the higher price), so not a single farmer will half their production.
- Do you have a method for pollination or do you let nature handle it?
- I hire bees when the trees are flowering. I need around 20 bee colonies, which is 2 colonies per hectare and approximately 40,000 bees per colony.
- Keeping bees myself would cost a lot of energy and time, so I do not do that. They are like pets, you need to take care of them.
- What do you think about the concept of a robotic bee / artificial pollinator
- It would be possible to pollinate artificially, it already happens a lot in china with labourers, who pollinate using brushes.
- It would be a shame if this would really be necessary. The problem should be solved by protecting the bees, but it is useful to research this anyway.
- Do you notice the reduction of the amount of bees?
- Not really yet. I think I'll be dead before the beeproblem gets too serious. I do not notice much difference because this land was too big to pollinate without bees before the decline of bees, and hired bees are still easy to come by.
- How much have you thought about pollination while planting your trees?
- I have thought about this a lot, because it is very important for the quality of your apples. There needs to be at least 30% of 'strange' pollen
- Have you ever thought about artificial pollination / do you think it is possible to create an artificial bee?
- Read a bit about it, but I have my bees, so it is not really necessary.
- Pollen inside of flowers is only ripe for a few specific hours, which is a different moment for every single flower. Bees can immediately notice whether pollen is useful, while a drone cannot do this easily. That is why bees stay on certain flowers longer than on others. Bees are very smart, if you can achieve to copy their ways and senses, you have build a great robot and you have found a golden business plan. This will be extremely hard to do tho.
- What would you expect from a robotic bee?
- I would go crazy if it makes a lot of sound, like drones do at this moment.
- Not too big
- It should not need adjustments of my orchard (like roofing in)
- What way should be spread the pollen? From flower to flower or first collect, then spray liquified pollen
- I do not know whether it is possible to suck out pollen out of apples, that is not my area of expertise.
- Liquifying is probably possible.
- If you can create specific air flows, you could pollinate through the air, but this is hard without adding a roof to the orchard.
This interview gave us a new insight in the bee problem and how to solve it. However, we did not agree with his solution for the problem. We would like to use technology to fix the problem, rather than let the decline of the human population get the bee population back in balance. His requirements for the robotic bee were very useful to create a drone design.
The things users will require the drones to meet are:
- The drones need to be energy efficient so they last long enough on one charge
- The flowers should not be damaged by the artificial pollination
- The drones must be fully charged in a short timespan
- The drones must be able to reach a charging station in time before a battery runs out
- The drones must be able to hover over flowers while collecting and pollinating
- The pollen must be efficiently collected from and spread on a flower
- The drones need to be charged efficiently; charging times should be similar or lower than flying times
- Charging should be safe for the environment and the users
- Charging should work no matter the weather conditions
Pollen collection and Pollination
For the research into pollination and collection we decided to narrow down the research and design by focussing on the pollination of apple trees. This was decided since there exist around 300.000 species of flowering plant in the world , making the design of a robotic bee suited for all species of flowers too complicated to achieve in the limited time that is available.
The apple tree was chosen since the apple is the most eaten fruit in the Netherlands, as well as an important export product. Furthermore, when it comes to pollination, the apple tree is self-incompatible, which means that it must be cross-pollinated to bloom. This would accomodate the testing of a prototype of robotic bee, since the self-incompatibility helps to ensure that the bee is the only pollinator.
Furthermore, since appleblossom grows all around the branches and thus also face towards the ground, the drone cannot land on all of the flowers in order to pollinate them. Therefore it was decided to focus on a drone that only hovers over the flowers while pollinating or collecting pollen.
For the collection of the pollen, two main methods can be distinguised.
Firstly, the pollen could be collected by means of touching the flower, causing the pollen to stick to the surface they make contact with. Bees use this method to collect pollen for themselves. The pollen are collected in the bee's fur and then transfered to pollen baskets on their legs for transport. Study shows that the density and length of the bees hairs is an important factor in the adhesion of pollen ; the relation between the diameter of the pollen and the spacing of the bee's hairs defines the difficulty of removal. When the diameter of the pollen is significantly smaller than the spacing of the hairs, the pollen settles deeply into the hairs. However, as the pollen diameter to hair-spacing ratio increases, the pollen are suspended between the hairs, which better facilitates the removal of the pollen.
This conclusion could be used to design a collection patch, by imitating the fur of a bee for optimal adhesion. According to the aformentioned research, the ratio of hair-spacing to pollen diameter should be 1 for optimal pollen adhesion. However, since apple pollen have an elliptic form, of on average 45 by 25 micrometer , the pollen will never exactly fit into an evenly spaced grid of hairs. Thus a hair spacing of the average, 35 micrometer, would be the best suited option.
However, a disatvantage of pollination with a patch is the precision required from the drone. Since the blossoms of an apple tree have a diameter of about 3 to 4 cm, the robot will have to aim precisely to be able to touch the patch to the stamens of the flower. Adding this to the fact that the robot will need to visit a large amount of flowers, the usage of a patch would be a relatively slow collection method.
Furthermore, since we aim to pollinate the flowers on scheduled times to optimize fruit yield, it is not desireable for the flowers to be pollinated unintentionally. When collecting pollen, the robotic bees will have to visit multiple flowers for collection before returning to the hive to charge and dispense the pollen, to be able to make the system efficient. As a consequence, a patch will already contain pollen that have been collected when the next flower is visited, risking accidental pollination. Thus, the patch will need to be designed in such a way that as many pollen as possible will remain stuck to the patch. However, it should still be possible to easily remove the collected pollen at the hive, when the bee returns to empty its storage. This could be achieved by using electrostatic energy.
Drones flying through the air will generate a small static charge on their surface just like a helicopter does. With plants having a slight negtive charge on them , as well as on their pollen grains, this means that the pollen will stick on the surface of the drone more easily. The same principle is used by bees already. Bees generate a small static charge on their fur while flying, which makes the pollen stick much better to their fur and so ensuring that the pollen don't fall off when flying.
We can use this static charge the drone generates to make the pollen stick better to the patch. When the pollen are collected from the flower and need to be stored in the hive, we can flip the polarity of the static charge so that all the pollen will fall off easily, since the pollen and the patch repel eachother. To make sure no pollen will fall of the patch, a charge needs to be put on the surface of the patch, preferably a bigger one then the one generated by friction between the rotors and small particles.
A second possibility could be collection of pollen by means of a vacuum cleaner type of attachment. The use of suction as a collection method would eliminate the problem of accidental pollination, as opposed to pollination by touching, since the collected pollen could be collected in a closed-off reservoir. Furthermore, the drone would need to be less precise when approaching the flower, since suction in the general area of the stamen would be sufficient to collect the pollen.
However, the method of suction itself is less precise than the touch-method. When using a vacuum cleaner there is a significant risk of sucking in unwanted material such as small insects or blockages of the system . In addition, the suction power should be well-balanced, enough to enable the robot to collect the pollen, but not damage the stamens or gynoecium of the plant. A last and important disadvantage of the suction method is the power needed to use the attachment. Since an essential part of the design of the robotic bee is its power usage and action-radius, additional electical components would influence the efficiency of the robot.
Storage and treatment
When pollinating with a solution of pollen, there are several factors to take into account. Firstly, pollen are very delicate when it comes to storage. Shaking the suspension or storing it a too high temperatures causes the pollen to burst and thus become unsuited for pollination. Furthermore, the ability for the pollen to germinate, which is necessary for succesfull pollination, while being stored or suspended, depends on the treatment of the pollen. When the pollen are hydrated before being suspended, the germination rates of the pollen increase significantly. Subsequently, the composition of the suspension liquid plays an important role in the germination rate of the pollen. According to research focussed on the conservation of pollen viability in several suspensions , a solution of calcium nitrate, boric acid and CMC (sodium carboxymethyl cellulose), each at 0.01%. However, a problem that remains is protecting the pollen grains while they dry on the flower, since the unprotected drying of the suspension causes the pollen grains to lose their capability to pollinate.
There are 3 ways for our use case to apply pollen to the flowers. Dry pollination, liquid pollination and just by rubbing it on. We would discourage pollination through rubbing immediately as it is a very inefficient way of applying. From all the options, it would cost the most effort to apply and the worst results. 
According to the article Artificial Pollination in Kiwifruit and Olive Trees , dry pollination and liquid pollination are both very viable solutions. Both options give very similar results if applied correctly. However, the tests were applied to kiwi fruits, but when they used the same tests on olives trees the researchers got similar results. This makes it safe to assume that this princple also applies to the apple trees. Further research is of course needed for concrete evidence on this.
The way they sprayed these kiwis is quite different from how we will spray apples, as they did not accurately target the flower when spraying instead of spraying the whole tree. In our case, we will spray precisely onto the flowers as spraying the whole tree wastes a lot of pollen. It is easier to accurate spray onto flowers with liquids than with a dust like substance as pollen. Hence, we will use liquids for pollinating apple tree flowers.
Since liquid pollination is in our opinion better achievable with drones than dry pollination, it was decided to have the drones pollinate the flowers with a solution of pollen. When doing this, there will also be an implemented pollination schedule. this would consist of spraying every flower in intervals of 4 hours at least 3 times. This will assure higher quality apples through full pollination as discussed in PRE2018_4_Group3_Literature#Seeds.
In a recent research project on the comparison between different pollination methods  , a suspension of pollen in water was used as one of the studied pollination methods. For this experiment the liquid pollination was done in two days. On the first day a preparation of 1.2 grams of pollen in 5L of water was used. On the second day the pollen density was doubled to 2.4 grams of pollen in 5L of water. According to the researchers, this resulted in a spread of 3 pollen grains per cm^2 after spraying. However, this pollination method resulted in only 10 apples per apple tree, which was traced back to the low density of pollen per cm^2.
In research into artificial pollination in kiwifruit trees , a pollen density of 12 grams of pollen per liter of water was used, along with a ratio of 50L of suspension per hectare of trees. Since this ratio of pollen per liter of water gave decent harvesting numbers, we can assume that this density is a good reference for liquid pollination. However, since this research was conducted on kiwifruit trees and not apple trees, we cannot know for sure this ratio will work for our research purposes. Furthermore, the suspension was sprayed all over the tree and not targeted directly at the individual flowers.
However, in research into the influence of pollination of kiwi fruit size is stated that 1mg of pollen per flower is needed to ensure commercial quality produce, but the researchers only sprayed the flowers once. From this we can conclude that 1mg solution per flower would be enough to pollinate.. We estimate that the drone will need to spray 1 ml of water per flower. From this follows that a concentration of 1 g/L would be sufficient.
In order to be able to design the robotic bee and its attachments, we will use an existing drone body as basis. There are several factors to take into account when selecting the correct drone.
A large drone usually has a larger battery capacity and could have a larger tank for pollen storage. A bigger drone is also less influenced by external factors, like wind. However, large drones damage the flowers rather than helping them with pollination. We made a consideration between these arguments to create good balance between the advantages and disadvantages of large and small drones. The drone we will use is the Tello drone and will be around 100mm by 100mm.
Functionalities of the drone
Since our objective is to develop a proof of concept of a drone attachment that will collect and transport pollen, we need to discuss how the attachment affects the performance of the drone that will carry the attachment. Because the drone will hover over apple tree flowers to collect and deliver pollen, the drone will not be similar in terms of its size, carrying capacity, and travel distances. Rather, the drones will transport pollen within the range of the charging station acting as hives for the bees and cover multiple apple tree flowers. The drones will not be able to land on the flower due to the size that is needed to carry large amount of pollen for multiple flowers.
Collection and pollination estimation
Apple trees, when cultivated commercially, produce around 600 fruits in a season . Combining this with the estimation that 90% of the flowers grows into an apple, a tree will produce around 670 flowers that will need to be pollinated.
Honey bees visit on average 9,2 flowers per minute according to research . However, since normal bees visit certain flowers for a longer amount of time in order to drink nectar, it is our estimate that the robotic bee will need 5 seconds per flower to be able position itself, collect pollen and move on to the next flower. In addition, the robotic bee will need 10 - 20 seconds to travel between the hive and the first or last flower.
The drone that is used as fundament for our robotic bee has a flight time of about 600 seconds or 10 minutes. If 100% of the power of the drone would be available for flight, it would mean that the robotic bee would be able to visit 114 flowers before needing to return to the hive to recharge. However, assuming that the robot will not be completely efficient, we assume that on average 100 flowers will be visited per trip.
With the assumption that a standard orchard has a tree density of around 250 trees per hectare , an amount of 1675 trips of 10 minutes would be needed to pollinate one hectare of apple trees. This would come down to 280 hours of work, excluding the time needed to recharge the drones.
This also means that 167.5 thousand flowers need to be pollinated per hectare and since the drones will polinate each flower three times to optimize the chance of a successful pollination, around 5000 trips of 10 minutes would be needed to pollinate one hectare of apple trees.
The drones have no more than 4 weeks to pollinate all flowers. The sun needs to shine in order to successfully pollinate the trees. Apple trees are fertile around the end of April. In this period, there were around 240 hours of sun the last few years. Rounded up, 50 trips per hour are required. A drone can make 3 trips in an hour, so approx. 17 drones are needed per hectare. We need spare drones as backup, which makes the amount of needed drones: 25.
Our stakeholder told us he would only use an artificial pollinator if it would not make too much noise. In his words, the constant buzz of a drone would drive him crazy. There are a few possibilities to make our drone quieter.
To cancel parts of the noise, noise-cancelling headphones use active noise control. This technique uses a microphone to measure the noise and uses a speaker to output the same noise in opposite phase, thus effectively cancelling it together. This technique might be usefull in our drones to eliminate the noise for bystanders. It has already been applied on drones successfully. This method adds quite some electronic components to the drone, which makes it a bit heavier and more expensive. As the added components also use power, a drone equipped with noise cancelling will not be able to fly as far as a drone without this hardware. We will therefore only try to add noise cancelling if the other options turn out not to be effective enough.
Reduce the RPM of the drone
The noise of a drone is generated by its high rotational speed. Reducing the RPM of the propellors will lead to a more silent drone. A smaller rotational speed needs to be compensated by increasing the radius of the blades in order to keep it in the air. A compromise needs to be found between size and noise. This can be done by testing multiple designs in practise.
Alter the blade design
'Northwest UAV' has used modeling software to optimize the design of the blade in terms of noise. Multiple cycles of prototyping and testing resulted in a propellor that looks like Batman's 'batarangs', thus in the shape of a bat-wing. This shape of blades will be tested on the artificial bees.
Use sound dampening materials
Noise reduction in flying machines is a hot topic in the research area. A new material was designed recently, which reduced noise in combination with the strategic placement of this material. It still has to be applied on machines like drones, but this method has a lot of potential.
Concentration and tank
An apple flower is around 5-10 cm in diameters, 0.5-1 cm in diameters consist of the area we need spray. This would take about around 0.5 ml if every drop of liquid the drone spray lands on this area. This would of course would not be reasonable. I would make an assumption that 50% of what we spray will land on this area. Meaning we need 2x as much water per flower. Out of the pollen collection, we would be visiting an average of 100 flowers. This would mean we have a total of 100 ml of liquid the robot needs to store.
When the robotic bees run out of energy, they return to their e-hive to charge. They also release the collected pollen here.
The 10x10 drone uses approx. 25W as calculated in Wireless charging possiblities and can fly around 600 seconds with a maximum speed of 7.75 m/s. As it will not fly in a straight line, but must pollinate the tree flowers in the meantime, we assume that the average speed equals half the maximum speed, 3.88 m/s. This means it can fly around 2.3 kilometers.
An e-hive needs to be able to power many drones simultaneously. If there is an e-hive every kilometer in the area, drones will not have to fly more than 2 times that distance before reaching the next hive, so 2 kilometers. This gives our drone some margin distance, so it can divert from its course a bit more for pollination and handle bad weather circumstances, like headwinds.
The 10x10 drone has a LiPo battery with a capacity of 1100 mAh. We assume it takes 10 minutes to charge the battery of one drone.
One of the possibilities to keep the e-hive energy efficient is to power them using solar panels. Solar panels cost quite some space. The standard solar panel has an input rate of around 1000 Watt per square meter, but you will only gain roughly 15-20% efficiency at best. A solar panel of one square meter with an efficiency of 20% will therefore be approximately 200 Watt. A day has approximately 5 sun hours, so the solar panel will produce around 1 kWh per day. This energy production depends on the weather of course. Because of this, solar power alone is not very reliable. The e-hive will still need power from other sources to ensure that the drones can always be charged. 1 kWh per day corresponds to 41.67 W, which is not enough to charge multiple drones at once.
As the e-hive are not that far apart, we will try to keep the solar panels small, which is why the solar panels will not be a lot larger than 1 square meter. The rest of the energy comes from the grid.
Charging and filling tank
The collected pollen will be collected at the e-hives in liquid form. Drones that are charging can also fill up their pollen storage.
To save space at the charging station, we looked at the possibility of charging while the drones are hovering in the neigbourhood of the hive, but this costs a lot of power, as the drone needs to keep flying. This article shows that it is possible using their GET system, but not yet in a range of more than a few meters.  and on their site . These drones are also way larger than the pollination drones. This gives them a larger charging area. In order to make it useful for our project, we would have to increase this range and make sure it can charge smaller drones. The consequence of this method is that the pollen needs to be refilled after each other instead of simultaneously.
The other possibility was to let the drones land on a platform and connect a charging cable. This increases the charge capacity a lot and makes sure the drones can fill up their pollen storage simultaneously, but this would increase the size of the hives significantly, as all the drones that charge at the same time need an own landing spot.
If we look at the current state of art of the drones and all the technical components needed to build the drone, the production of robotic bees would be feasible. Small drones already exist and, looking at the battery capacity and the research and development of even better batteries, the flight time will not be a problem.
Currently it is already possible to quickly charge the drones or even charge the drones while they are in the air. In the coming decade these techniques will be improved, so there is no bottleneck in the charging functionalities. Furthermore, cameras have become much better over the last couple of years and therefore, using those cameras to help navigate around the flowers and to the right position will be fairly easy. Thus there is low risk of harming the flowers by flying against them. With all the technology available at this point in time and looking at the trend of the development it is safe to say that the feasibility of the robotic bee will not depend on technology.
Another thing that might cause a problem will be the pollinating techniques, and the quality of the fruit. Flowers that are not correctly pollinated will grow into not perfectly round apples or even no apple will grow at all. This is something that should be avoided, because only the apples will bring up money for the user. The pollination technique (might be slightly changed if we have a final result) that we use can in theory pollinate every flower sufficiently, but this needs to be verified by tests that can be done after a prototype is build. The technology available at this point will definitely suffice for building and testing the pollination parts of the drone. However, even without testing, taking into account that the flowers will be sprayed upon multiple times, the chance that it will be pollinated well is very high.
The only problem that could still exist is the price tag of the drone. Since a standard drone of the size chosen for this project is around €99,- and a lot of drones are required for pollination, the drones themselves will be quite expensive. Subsequently,the nozzle and the tank need to be build and placed on the drone. Lastly, charging stations and the pollen collecting patch need to be designed and made. So all in all the drone would be quite expensive. However, taking into account that all the materials are going to be mass produced, the price for 1 drone should be somewhere in between €100 and €150 .
When renting beehives to pollinate an orchard it will cost around €60 per beehive per move. In which a move is defined as the transportation of the beehive to a new location. The Philips Fruittuin we interviewed needs 20 beehives to pollinate its whole orchard, which is around 10 hectares. So the total cost per year using this method comes to €1200 to pollinate the trees.
For a field of this size we would need 250 drones to pollinate everything within the time frame in which the flowers are fertile. Current electromotors have a life span of around 2 years. If research and development is capable of improving the life span of the motors, the durability of the drones will increase. This means that repair costs will decrease over time since the drones will last longer. Therefore the drone could be a viable option if farmers and companies want to make sure food productions stay on the same level and if the bee population drops in the upcoming years.
State of the Art
- ↑ http://www.theplantlist.org/browse/A/
- ↑ Honey bee hairs and pollenkitt are essential for pollen capture and removal, Guillermo J Amador et al 2017 Bioinspir. Biomim. 12 026015, https://doi.org/10.1088/1748-3190/aa5c6e
- ↑ Pollen Morphology Of The Genus Malus (Rosaceae), V. Nazeri Joneghani, 2008 Ir. Journ. of Science&Technology, vol 32, n A2
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- ↑ Meng-Ying Tsai, Su-Hwa Chen, Wen-Yuan Kao,Floral morphs and seed production from hand-pollination in a population of Oxalis corymbosa in Taiwan, Flora, Volume 226, 2017, Pages 89-95, ISSN 0367-2530, https://doi.org/10.1016/j.flora.2016.11.011. (http://www.sciencedirect.com/science/article/pii/S0367253016301852)
- ↑ Hiroshi Shimizu, Taito Sato, Development of strawberry pollination system using ultrasonic radiation pressure, IFAC-PapersOnLine, Volume 51, Issue 17, 2018, Pages 57-60, ISSN 2405-8963, https://doi.org/10.1016/j.ifacol.2018.08.060 (http://www.sciencedirect.com/science/article/pii/S2405896318311765)
- ↑ Tacconi Gianni and Michelotti Vania (June 6th 2018). Artificial Pollination in Kiwifruit and Olive Trees, Pollination in Plants, Phatlane William Mokwala, IntechOpen, DOI: 10.5772/intechopen.74831. Available from: https://www.intechopen.com/books/pollination-in-plants/artificial-pollination-in-kiwifruit-and-olive-trees
- ↑ Kubersky, U., Boecking, O. & Wittmann, D. 2005, "Are pollen spraying and pollen dispensers alternatives to conventional pollination by bees for apple trees?", Erwerbs-Obstbau, vol. 47, no. 5, pp. 117-123.
- ↑ Tacconi Gianni and Michelotti Vania (June 6th 2018). Artificial Pollination in Kiwifruit and Olive Trees, Pollination in Plants, Phatlane William Mokwala, IntechOpen, DOI: 10.5772/intechopen.74831. Available from: https://www.intechopen.com/books/pollination-in-plants/artificial-pollination-in-kiwifruit-and-olive-trees
- ↑ A. Alspach, P & Pyke, Nick & G. T. Morgan, C & E. Ruth, J. (1992). Influence of application rates of bee-collected pollen on the fruit size of kiwifruit. New Zealand Journal of Crop and Horticultural Science - N Z J CROP HORTICULT SCI. 19. 19-24. 10.1080/01140671.1991.10418101.
- ↑ https://wikifarmer.com/apple-tree-harvest-yields/
- ↑ M.J. Couvillon, C.M. Walter, E.M. Blows, T.J. Czaczkes, K.L. Alton, F.L.W. Ratnieks, "Busy Bees: Variation in Insect Flower-Visiting Rates across Multiple Plant Species" Psyche, vol. 2015, Article ID 134630, 7 pages, 2015. https://doi.org/10.1155/2015/134630.
- ↑ https://wikifarmer.com/planting-apple-trees/
- ↑ http://www.zonurencalculator.nl/sun_hours_calculation
- ↑ Castro, Victor et al. “Active Noise Cancellation System for UAVs.” (2017).
- ↑ A. Liszewski, New Noise-Blocking Material Could Make Jets and Drones Super Quiet, 12-03-2019, https://gizmodo.com/new-noise-blocking-material-could-make-jets-and-drones-1833229326
- ↑ https://www.teslarati.com/wireless-charging-drone-in-air-ces-global-energy/
- ↑ http://getcorp.com/