Pit Talk: The word 'efficiency' and Drone Racing

I’ve had a lot of conversations about quads with the local Pilots and others, and I wanted to bring up the discussion about efficiency. There is a lot of talk about this word and I think the issue has been clouded and I want to share my view on the topic.

Efficiency is a great concept with our drones. Ideally, we would love a lot of performance and a lot of flight time, but the reality is at the outer limits these are mutually exclusive. I’m not alone in this, it is a fundamental truth of vehicular systems design. 

What do I mean by this? I can explain it in a very simple fashion. A high performance vehicle consumes more fuel than a sedan. A vehicle designed for efficiency is a completely different design direction than say a Lamborghini. Look at the student built car that gets 3,587mpg (http://www.wired.com/2013/04/3587-mpg-student-car/). When vehicle designers build a system, they have to build it to a purpose. And both these examples are, albeit extreme, there to illustrate my point. The Lamborghini goes for absolute in driving performance while the student car goes for the absolute in efficiency performance.

Where I get contentious is when people talk about efficiency and drone racing platforms. Efficiency only matters in a racing platform when there is a limit to available power or duration is a concern (or typically both). Even when that is the case, you want to extract the absolute limit of power, while achieving your target efficiency. F1 is a perfect example of this. They have fuel caps, power limits and used to have fuel stops. We do not have any of this in drone racing. At least not yet. So efficiency in a racing platform means something completely different. 

It is my contention that efficiency in the current state of drone racing means having the absolute lightest frame that can survive a crash, producing the maximum thrust you can handle with the least amount of battery you can hold to get your number of laps done.

Lets break this down in to the components. The lightest frame has multiple implications. 1) Light means dexterous in our current racing format. The more dexterous your aircraft is, the quicker it can respond to your inputs. 2) A light airframe means that all of your electronics don’t have to work as hard. 3) A frame shouldn’t be a tank to survive a crash in a racing environment and we don't have pit crews and tons of replacements available to us like an F1 team does. I’ve seen frames go too thin, using flexible 1mm carbon which, while strong when bolted together with standoffs, is not going to survive much at the speeds 250’s are capable of. So responsive, less electronics strain, and lightweight but survivable. 

Next, lets evaluate what I mean by, ‘producing the maximum thrust you can handle with the least amount of battery.’ In the current formats of quad racing, racers are only required to make a few laps. So, in theory, your battery should only last you that set of laps, carrying any more than that wouldn’t be efficient because you’d be carrying weight you don’t need. F1 adhered to this principle. When fuel stops were in place, teams ran just enough fuel to complete the laps they’d cover between stops.

You can achieve the same result by either reducing the battery capacity or producing more thrust. So I think it behooves racers to find the thrust to weight ratio they are most capable of harnessing. My new prototype is exceedingly light, and with the right power system can achieve nearly a 10:1 thrust to weight ratio. At that power level, max flight time at full throttle is a minute on a 75C 4S 1300mAh battery. More than sufficient for a 3-5 lap race in the hands of a Pro Pilot.

So when I designed my latest airframe, I intended it to be as light as possible while still surviving the odd crash and the power system I'm running is equally light but I will be testing at what power to weight ratio I'm most comfortable with. Only then will I be able to extract the performance I'm capable of as a Pilot. 

The point I’m making is that the blanket term of efficiency is often over simplified in it’s use these days. One must clarify their intended use for a given platform. Many of you have multiple airframes built with a variety of parts - why aren’t you building one for racing, park flying, long duration and so on?

I've spoken about the racer, so lets discuss the park flyer. A park flyer, by design should be more battery efficient. When you’re at the park you want to get the maximum flight time and the most performance (not maximum performance as that means less flight time). Having to change a battery every minute or two doesn’t suit the plan of flying for fun, but you don't want your airframe to be a slouch, otherwise you'd have no power for maneuvers or tricks. However, in contrast, when you have to swap your seat for the next heat of racing, battery swaps will happen too because a fresh pack means max power in your next race.  

So when you take your battery 'efficient' park flyer to a race event is like taking a Subaru WRX and pitting it against somebody’s Lamborghini on a track. Sure they both have 4WD and are built with performance in mind, but the purposes are different, the Subaru,  a daily use car and a rally capable machine, the Lambo, a supercar chasing the pinnacle of on road performance. And ultimately the person who has designed their build with a pure performance machine philosophy (and has practiced with it extensively of course) will beat out the similarly experienced Pilot flying a more ‘efficient’ setup.

In my conversations with my friend Tyson (check out his instagram here), he made the an excellent point. If you tried taking the Lambo off-road versus the Subie, the Subie would be able to get ahead in the race. Why? Because it is suited to that environment, much like a 180 would be a better choice for a short-course over a 250 or 300mm platform. It is decisions like this that will not only give you, the Pilot, an advantage over those who think about it, but your choices for a racing platform will be their most efficient. So see, this issue has multiple dimensions and bandying the word efficiency has little meaning outside of purpose and environment of use. It is a third level definition, one which can only be defined when the other two are answered first.  

The last point of discussion in this conversation about efficiency, came from my good friend Steve Ramm of Aerosim Research. If we really want to take the discussion to it's rightful conclusion, in racing cost is a factor. I'm using 6K, USA made, dry carbon, a much more exotic and higher quality carbon than the 3K Chinese wet lay-up carbon most frames are using. It is stronger and lighter but with this comes cost. On one hand, it means I can get more strength and explore thinner geometries or more robust geometries, but it is more expensive to the end user. And while some cost conscious racers may not see the value, in time this will matter more and more for the competitive edge. Rising costs in the pursuit of efficiency and performance is inevitable; this is why we have racing classes in the automotive world, because if 'there's one place where F1 excels, it's spending a ton of cash for a hundredth of a second.'

In conclusion, as we grow, I hope you will be more thoughtful about your builds and your designs. Think about your intended environment and usage scenario. It makes a huge difference in the experience and the choices in your hardware. Are you going to be racing, flying for fun or some other agenda? Are your racing events typically tight and twisty or large outdoor open spaces with large gaps between them? All of these questions matter and can sway your setup in one direction or the other. We must establish these definitions clearly and to optimize our choices accordingly. This is all soo young, soo early, soo exciting and we have so much to explore, define and understand. Lets do it with focus, drive and determination. 

 

With best intentions

Sherif