Whether you're a first-time flyer or in the market for a serious autonomous aircraft, you need to read our robotics engineer's guide to finding the drone that best suits your application.
What is a drone?
The word 'drone' was initially used to describe an aircraft that can fly autonomously - that is, without the assistance of a human operator. The problem these days is that the definition of 'autonomous' becomes blurry.
If you are controlling its movement forward, backwards, left and right but the drone is regulating its own height, is it flying autonomously? Probably not. The Sydney Aerospace and Defence Interest Group (SADIG) is currently working on an industry definition of the term 'fully autonomous', as this will be required before standards can be put in place. Without such standards, drones cannot be properly regulated for commercial use.
This is a debate for another time, however. For the purpose of this article, let’s assume a drone is an aircraft that can be flown with the simple click of a button and a bunch of GPS waypoints.
How many types of drones are there?
At a general level, the form of a drone can be divided into two categories: multirotor and fixed-wing. From a user interface perspective, these basically operate the same way: you pull out your ground station, enter a few GPS waypoints and hit take-off. The drone flies its mission and returns. Where the two start to differ is from an operational point of view.
Typically, a multirotor drone typically an aircraft that has three to 16 electric motors (with props) fixed to a frame. The props are parallel to the ground so they can provide upwards lift. The only real exception to this is a helicopter, which has one big, variable-pitch lift prop and a second smaller tail prop for stabilisation. A multirotor can take off vertically and hold its position in the air. It is, with the exception of the helicopter, very simple mechanically. The motors and props are fixed, and the movement of the aircraft is controlled by varying the speed of each motor accordingly.
A fixed-wing aircraft typically has one motor at the front (prop perpendicular to the ground), which pulls the frame forward. A series of electronically controlled flaps (Aileron, elevators and rudders) are used to steer the aircraft. An exception to this is a glider-style set-up. Usually, a fixed-wing has a central motor that is mounted in the reverse direction (so it pushes instead of pulling). It has just two flaps (elevons) that are used to steer it.
Tips for purchasing like a pro
1. Multirotor vs fixed-wing: how to determine which drone type best suits your application
OK, so now you know there are a couple types of drones. You’re probably thinking, 'Which type do I need? What are the pros and cons and which drone best suits my application?'
Let’s have a look at each type to help you figure out the direction you want to go in.
A multirotor design is the most manoeuvrable type of aircraft. Is can take off and land vertically, so your runway only has to be big enough to place your aircraft level (with perhaps a little extra space for error in GPS if you are doing autonomous flying). You can literally fly a multirotor off the tray of your ute! A multirotor also has the ability to hold its position in the air and it can rotate on a dime. This makes it perfect if you need to stop and take a close look at a damaged fence-line via the on-board camera. Perhaps you want to inspect the structural integrity of your antenna tower or windmill? This is where the multirotor will shine. A multirotor can also carry much heavier payloads than can a fixed-wing drone of the same size.
Unfortunately, to have all this manoeuvrability, we have to lose efficiency. A multirotor is all energy. Its design means it cannot power off its motors and glide freely with the wind. It must always be maintaining its 'hover throttle' - the minimum speed the motors are required to turn in order to keep the aircraft in the air. This makes a multirotor drone bad for long 'endurance' tasks such as coverage of thousands and thousands of hectares.
If you need to cover some serious distance, you'll need to start thinking about a fixed-wing drone. These guys will fly for hours on a single battery charge. They can also move quickly. So if you need to do some aerial mapping of your property, then you want a fixed wing.
Keep in mind, however, that with a fixed-wing, you no longer have the advantage of vertical take-off and landing. Most fixed-wing units require a launcher to get the aircraft up to speed quickly for take-off. Having to lug a launcher around with you can be a burden. Then you also need an area of at least 20 by 100 metres for the plane to come in and land. If you’re working somewhere where there isn’t open space, a fixed-wing can be tricky. Because they also lack some manoeuvrability, turning requires extra space: the fixed-wing needs to have room to right itself before continuing on its mission.
Below, I've put together a shortlist of application features that may help you decide on which drone type to get:
Buy a multirotor if:
- your estimated round-trip distance is less than 60 kilometres;
- you need to be able to take off and land in areas without open space (e.g. in an orchard or vineyard);
- you need to be able to fly a very precise flight path with the ability to stop at any time during your mission (e.g. for a fence-line inspection); and/or
- you want to carry a large payload (e.g. spot spraying).
Buy a fixed-wing if:
- your estimated round-trip distance is greater than 60 kilometres;
- you need to map a large area (e.g. for crop-health imaging in big paddocks); and/or
- you’re operating in a large open area.
2. Accessories and design: Know what tasks your drone will be performing
By now, you'll have made up your mind on the type of drone you need. The next step is to make sure you have a clear idea of what you need the system to do. Below are a few simple questions to which you should know the answers before you purchase accessories and/or decide on the final design of your drone.
How long do you need the aircraft to stay in the air before a battery change or re-fuelling is required?
Battery charge time
This is the amount of time required for the drone's batteries to charge. The obvious answer here is ASAP. But all batteries will be restricted to a minimum charge time, based on their specs. What you need to figure out here is how long you need the aircraft in the air to perform its purpose. If you need to keep a multirotor drone in the air for an hour but only get 10 minutes of flight time, you will need multiple batteries to keep it going for the entire task. If you only want to buy two sets of batteries, you are going to need a charge time of 10 minutes or less to keep the aircraft working constantly. You might decide you don’t want to be charging in the field; in this case, you will need six sets of batteries to get your hour.
This is measured as the approximate distance between diagonally opposite motors in multirotors, and as the wing span in fixed-wings. Ultimately, you will have to transport this thing, so you need to make sure it will fit in the vehicle that will carry it. Typically, the bigger the aircraft, the longer it will fly for but the more it will cost. Most of the time, if you have answered all the other questions, you won’t be left with much choice in the dimension department anyway - but it's still something to consider.
What is it that you need the aircraft to carry? Is it a little camera (like a Go Pro)? Is it a 30L tank of pesticide? Both are possible but there's about a magnitude of seven to 10 difference in price point.
How fast will the aircraft travel with respect to the ground? This can be an important consideration when you are try to map large areas within a given battery time. Knowing an aircraft can fly up to 100km/hr for 30 minutes means you're really only going to be able to fly the drone a distance of 50 kilometres round-trip (or 25 kilometres away from yourself) before it will need to come back. If the retailer doesn’t provide details on the distance that can be covered by the aircraft, make sure you know the speed you need the craft to go for its given flight time. You don’t want to pull up short on this one!
You need to know what type of radio link the drone has and the distance you can get with it. Typically, you will be buying a radio (or telemetry) link in one of a few frequency bands: 433Mhz, 900Mhz, 2.4Ghz or 5.8Ghz. The lower the frequency, the longer the range; however, the lower the frequency, the less data you can get back at once. So if you want a drone that streams video back the whole time, you will probably need a 5.8Ghz radio link. If you don’t need video and want to cover some serious distance instead, you’re looking at the 900 and 433 area of the spectrum.
Regardless of the specifics of your application, all drones should come with the following:
- radio for telemetry;
- an RC transmitter for manual control (a requirement of CASA);
- a battery charger;
- a ground station (some drone manufacturers just provide you with software that allows you to use a tablet or computer as a ground station - if this is the case, make sure you have a device that allows you to install that software);
- spare parts (extra batteries, based on your flight time; spare props in case you clip something, et cetera); and
- sensors (this will vary depending on your application: Does it have a mapping camera for mapping? A video camera with appropriate data link for live viewing?).
3. Consider buying crash and accident protection
You have purchased your system - do you need to insure it? Like all things, this needs to be considered on a case-by-case basis. If you are spending only a few thousand dollars on a drone, it might not be worth the cost of insuring it. If you're using your machine commercially, however, you will need insurance. This protects you from those times when a sudden dust storm takes down your drone mid-flight, or the drone clips a tree branch as it is searching for stray ewes. It’s more about the third-party side of things here; often, you can get drone insurance bundled with your business’s current insurance package.
If you’re just flying as a hobbyist on private property, then I think you could save yourself some dollars here. It is about assessing the risk based on your regular operating environment.
4. Get the correct license for operation
Now you are fully insured and ready for flying. Do you need a license? Well, it depends.
Are you flying for commercial purposes? If so, then you will need to be fully certified. As a hobbyist, you do not need licensing but will still need to adhere to some rules to ensure the safety of others (see the RPA safety image below).
For commercial use, you will need two things: a remotely piloted aircraft systems (RPAS) certificate and a UAV operators certificate (UOC). The RPAS will take you about a week of training and cost you around $4,000. You then need to apply to CASA for a UOC. This will cost you around $1,200 and it will take around six months (at time of writing) for the application to be processed. You can’t complete the UOC without having a chief pilot. The minimum requirement for a chief pilot is to hold an RPAS. If you already have a commercial pilot's license, you need not acquire the RPAS.
5. Tool vs toy: How to spot the difference between them if you're purchasing your drone online
These days, when you go online, you will be inundated with advertisements for numerous different types of drones. Unfortunately, not all drones are created equal. When purchasing from cheap online vendors you must be aware that, in getting that drone for a reduced price, you will most likely be trading off quality and functionality.
Here are some key difference between professional drones (tools for the working man/woman) and their cheaper counterparts (toys):
- The transmitter – a toy drone will come with its own transmitter, used for flying it around. Usually, these will be designed specifically for that model and you won’t be able to interface any other transmitter with it. A professional drone will have support to allow you to sync a heap of proper RC transmitters to it.
- Autonomous flight – a toy typically won't come with a ground station or support any of the interesting functionality you will find in a high-end drone. Be aware that if you want it to fly itself, you’re going to need to spend a little more cash.
- Batteries and chargers – usually, a toy drone will have a small battery with it that you can charge only using the manufacturer's specifically branded charger. This results in poor flight time and long charge times. Some don’t even have external chargers and require you to plug the drones in to power points, which means you cannot be charging batteries and flying simultaneously. High-end drones will support standard lithium polymer batteries with generic connectors. These can be charged off an array of lithium polymer chargers and allow you to fly and charge simultaneously.
- Video – if you find a cheap little drone with built-in video, don’t get too excited. These built-in cameras are typically low-quality and the video links they generate will be grainy and delayed. Professional drones allow the user to attach various types of cameras and to upgrade the transmission link. This ensures you can get the image quality you require.
- Spare parts – unfortunately, a reality of flying anything is that it won’t always come down as gently as it should. If it does land badly, it will most likely require some spare parts to get it back up in the air. The toys will not come with, or have readily available spare parts - you will be expected to buy a whole new unit. The professional drones will have every little par covered, from landing gear to prop blades. This is not only good for crashes but is also useful for any upgrades you may be able to foresee.
6. Warranties, spare parts and repairs: the advantage of purchasing direct from a manufacturer
Now, don’t get me wrong here; the internet is a great place to get good deals if you know what you’re looking for. If you’re not quite sure, you are better off purchasing direct from the retailer. This ensures you can ask the questions that I've previously mentioned you need to know. You will also be covered by any warranties the retailer offers. A good retailer can also help you to source spare parts and upgrades for those sad times when flying doesn’t quite go to plan.
Cameron Owen works for RoboticSystems.com.au