Drones have been a revolutionary technology, giving practical access to the sky for a whole class of individuals and businesses that would never have the money for full-sized aircraft.
The film industry has taken to professional drones like ducks to water. These days even low-budget indie movies are rife with sweeping aerial shots.
We’re also starting to see drones used for other purposes. They’re being used for power line maintenance, that is drones with flamethrowers are being used to burn debris from power lines.
Drone cargo services are also becoming a thing now, with Amazon Prime Air being the most famous example. It might not be a strange sight in the coming years for small cargo drones to flit across the sky.
Every day there are more and more use cases for small drones, but almost all of these drones suffer from the same problem: low flight endurance.
Why? The main culprit is the lithium-ion battery technology that powers almost every drone in the sky today.
New Kid on the Block
Battery-powered RC aircraft and UAVs are a fairly recent development. Just a few years ago almost no one at a radio controlled aircraft meet had battery-powered craft.
The reason for this was mainly that the best commercial battery technology was simply too heavy for the amount of power that it carried.
That changed with modern lithium-ion batteries. Finally batteries had a energy-to-weight ratio that made them practical and even desirable for RC craft.
The problem is that you can only pack so many pounds of battery into an aircraft before you hit diminishing returns. This is why even big industrial drones like the Matrice 600 Pro top out at 35 minutes of flight time.
This is a problem if you want to use a drone for long-distance work or need them in the air for hours, not minutes. Right now fully-electric lithium ion drones simply can’t live up to those demands.
To understand why we have to look at the energy physics of lithium ion batteries compared to that other common power source: gasoline.
Batteries vs Gasoline: The Showdown
Gasoline is a refined fuel made from crude fossil sources, which can include crude oil and coal. We can also use biological sources such as corn to make similar kinds of fuel, but in general it’s still worth more as actual food at this point.
One of the main reasons gasoline and other liquid fossil fuels have become so dominant is because of their high energy density. Energy density is a measurement of how much energy there is in a given amount of a fuel. So we can say that it has a certain amount of energy per gram or per cubic centimeter.
Comparing the energy density of lithium ion batteries and gasoline shows that gas has 100 times the energy density of a lithium battery.
That’s a huge difference, but it isn’t the whole story. The usable energy you can get from a fuel depends on how efficient your method of freeing that energy is. Even modern gasoline engine technology is relatively inefficient, with most of the energy in gasoline not powering anything useful, but wasted in some way.
The energy we actually get out is much less than the total energy in the fuel. Here lithium ions beat gasoline by a big margin. Lithium batteries are highly efficient with efficiency figures over 90% depending on conditions. Gasoline engines on the other hand are terrible in this regard, with even the very best internal combustion engines hitting efficiency rates of only 37%.
This helps to level the playing field, but even so batteries would have to reach one fifth of gasoline’s energy density before they would be equal in practical terms. Going from one hundredth the density to one fifth is a tall order and it won’t happen soon. Estimates for parity between gas powered cars and electric ones is estimated to come around the year 2045.
Gas Powered Drones
To you and I this means that if you want more than half and hour of operational time in your small non-gliding UAV, you need to think of an alternative way of powering it. Which is why we’re seeing more and more drones that have a tank of fuel and a small internal combustion engine providing the power.
Ultimately the motors on these gas powered drones aren’t usually driven directly by the engine, but by electrical energy provided by the engine acting as a generator.
This is the same approach taken with the new generation of hybrid cars, where a small gasoline engine charges up the batteries and/or provides power to the electric motors directly. This is more fuel efficient than a direct power-train, because the engine always runs at an optimal speed to get the most electricity at a constant rate. In those cars you also don’t make use of the gasoline if a trip is shorter than the battery capacity. A good example of this is the BMW i3 with the REX extender option.
There are quadcopter that direct-drive power, repurposing the same technology that “nitro” remote control helicopters have been using for years. A good example is the Nitro Stingray, which you can see in this video:
Of course, the Stingray is designed in such a way that one central motor drives all the rotors, with collective pitch controls varying the thrust. Whether that motor is electric or gas powered.
Whether hybrid or gas-only, this introduces some of the disadvantages of gasoline engines to drone flying. For one thing, they’re noisy.
Everyone knows the “swarm of angry bees” sound the typical drone makes, but now you can add the sound of a small motor to it as well. It’s not such a big deal though, because the use case for gas powered drones is mainly for drone that have to fly high up and over long distances.
Electric drones are still a better choice for urban applications.
Where Do I Sign Up?
At the moment actually getting your hands on an actual hybrid drone is easier said than done. Most examples you’ll find on the web are custom machines built for a specific job or as a proof of concept.
That doesn’t mean these drones are not for sale. There are already a few companies either with a product in the wings or who are looking for funding. One that you’ll probably be hearing more from is Quaternium. With their Hybrix hybrid drone.
The Hybrix 2.0 looks as polished as anything that DJI have for sale today, but out of the box you get 2 hours of flight time at maximum payload. How much weight? Try a 20 KG maximum takeoff weight on for size.
For comparison, the Matrice 600 Pro has a MTOW of 15Kg, which gets just over 30 minutes of flight. It feels like this is hyperbole, but here’s a timelapse video of the Hybrix hovering for two hours straight, fully loaded.
The payload is a less-impressive 2KG, so you won’t be using this to lift a big professional cinematic camera just yet. There doesn’t seem to be clear pricing, but the company seems more than happy to give you a custom quotation. My guess is that it ain’t cheap.
Qauternium isn’t the only game in town either, there’s also Pegasys Aeronautics, who are also punting two hour flight times, but they aren’t selling an entire drone. Instead we have the GE35 Range Extender, which converts an existing drone into a hybrid unit. Pegasys says that the GE35 is a straight swap for your current drone batteries and doesn’t require much modification.
The Fuel Cells Are Coming
There’s another alternative power source for drones waiting to swoop in from the sidelines and that alternative is fuel cells.
If you’ve never heard of a fuel cell before, it’s actually pretty easy to understand. Like a battery, you get electricity out of a fuel cell, but the way that it produces that energy is different. The fuel cell uses hydrogen to drive a chemical reaction that makes electrical power. To refuel, you just replace the hydrogen.
Hydrogen electric cars have a lot of potential, because they can give a similar experience as current gas powered cars. You don’t charge it up overnight or over hours. You just pull into a filling station and get your hydrogen topped off. Meanwhile, the only exhaust of a fuel cell is harmless water and some heat. It’s a very clean system depending on how clean the source is you’re using to create the hydrogen.
Fuel cell technology is so clean and powerful that there have been successful attempts at miniaturizing them for use with laptops and smartphones. In one test an embedded fuel cell powered a smartphone for a whole week!
If these micro fuel cells can power consumer electronics as small as a smartphone, then perhaps drones can benefit too.
Fuel Cell Drones
There have been quite a few demos of drones powered by fuel cells over the last few years and there are already products ready for purchase by customers in certain industries, defence organisations being a prime example.
MMC UAV has already produced a second-generation fuel cell drone named the HYDrone 1800. It’s a big boy, but with that size comes some serious endurance specs. The claimed maximum flight time of the HYDrone 1800 is a staggering four hours. Refuelling the drone takes one minute. That’s a big jump from what industrial drone customers are currently used to.
There are a lot of reasons that hydrogen fuel cells are better than both batteries and gasoline. They are more efficient than gasoline, with up to 60 percent efficiency with current units. Hydrogen is not as energy dense as gasoline, but does way better than lithium without the noise, pollution and vibration.
Overall fuel cells seem like a no-brainer, but boy is it expensive to implement. The creation, storage and distribution of the hydrogen itself is currently a big problem.
So the first customers will be ones that really only care about performance and not price. Small military UAVs and applications in other government sectors as well as the oil and gas industry seem like likely places we’ll see fuel cell technology for drones implemented first.
Is The Battery Dead?
None of this means that battery technology is out of the race in the long term. There’s a lot of money and human capital behind the drive to improve battery technology. It may feel like batteries really aren’t advancing that quickly, but if you had to compare capacities and charging times in current generation lithium cells to those of ten years ago they’re quite a lot better.
There are a lot of potential ways batteries can be turned into “super batteries” and researchers all over the world are racing to make those breakthroughs. In fact, we constantly hear about revolutionary discoveries made in labs that promise to give us batteries with ten times the capacity and almost instant charging. However, implementing those discoveries into production batteries usually throws water on such claims pretty quickly.
Earlier this year the man who actually invented lithium ion batteries, John Goodenough, announced a breakthrough that simply seems too good to be true. According to the highly respected scientist their discovery would almost immediately bring battery technology on par with gasoline in practical terms, but so far we don’t know if his claims have any merit
Strength in Diversity
For us as consumers who simply want drones that can fly long distances or stay in the air for hours it probably doesn’t matter which solution ends up winning in the marketplace.
It does however matter that there is strong competition to bring the world the next energy revolution.
We as consumers can only benefit and it never hurt to have options when you’re trying to solve a problem.
Right now lithium battery technology is holding the potential of drones back, but the time is right to think about what you would do if you were unshackled from their constraints.
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