Single or Multirotor Rigs For Professional Drone Aerial Cinematography?
With the exponential increase in sightings of multirotor aerial rigs, one might think that they are the cat’s pajamas for low altitude aerial cinematography; and in some cases, they are the perfect tool for the job. But one might also be led to think that they are far superior in every aspect of close range aerial cinematography. But to assume this would be a serious error.
The primary reason for their sudden increase in popularity centers around the fact that, to a great extent, the on-board flight control system does most of the actual flying, with the pilot left to provide occasional control inputs to guide the rig along the desired flight path. Without this flight control, these aircraft are quite unstable. This assistance with control allows many lesser skilled pilots to quickly get into the aerial filming game.
Another difference is, compared to the traditional single rotor platforms that were the early mainstay in drone filming, the need for advanced mechanical skills is removed. Many multirotor systems are now available, turn-key, that only require firmware updates and minor maintenance to keep in the air. This is a huge benefit for those with little or no previous experience with flying machines.
There is a rapid shift in the commercial drone industry today towards “ready-to-fly” or RTF rigs. And so, vendors are perfectly happy to lead the uninitiated into thinking this is a buy/charge/fly/film proposition. It is impossible to appreciate the various skills needed to safely operate a heavy lift aerial rig proficiently until, in many cases, it’s too late. Many of our recent clients have reluctantly admitted to us that they had purchased these rigs and promptly proceeded to confirm Newton’s first law of motion with them. All one needs to do is ask around camera rental houses to hear horror stories of Red Epics plowing into the ground attached to a variety of “heavy lift” octocopters. There is a very good, and hopefully obvious reason, why senior commercial airline pilots are excellent, highly skilled pilots, even without using advanced auto flight systems.
When we first started out, 10 years ago on our adventure to provide cinema quality aerial filming from RC platforms, we thought that the most important thing we needed to learn was how to not let the vibration and unwanted movements of the helicopter disturb the cameras images. Granted this was a major challenge at that time but we also learned there was so much more we needed to know. Things like dealing with changing wind intensity and direction, crew safety, not running into things (situational awareness), staying focused on the task under time pressure and multiple distractions. All of these skills did not come quickly or easily. Please keep in mind that these observations are coming from one of the world’s most experienced, world-class professional RC pilots. Even with over two decades of top level flying experience, there was still an enormous amount to learn to be fully qualified to fly on a movie set.
It is often said that true learning follows the 70-20-10 rule, whereas 70% is learned by doing, 20% by observing others with experience and the last 10% by more formal training. This certainly applies to becoming a proficient aerial filming pilot.
Because of the rapid proliferation of multicopters, there continues to be a corresponding amount of misinformation surrounding them related to single rotor platforms.
1. “Multirotors are more stable than single rotor helicopters.” False. A single rotor helicopter is far more aerodynamically stable. Using a very sophisticated flight controller, the multirotor is slightly more stable than a properly tuned single rotor platform – sans autopilot. This same flight control technology is also available for single rotor helicopters, which, if used, yields a platform that is far more stable in high winds, taking advantage of its inherent stability combined with flight control.
2. “Multirotors are more efficient than single rotor platforms.” False. Using the same flying weight and camera payload, and using the same battery voltage and capacity, the single rotor helicopter provides more total thrust and endurance. Because approximately 15% of the single rotor helicopter’s power output is used for torque compensation (driving the tail rotor) some mistakenly think this throws the advantage to the multi. Even with this portion of total power not going to overall lift, the single rotor will still outlift the multirotor by 20%-30% due to the larger aerodynamic economies of scale.
3. “Multirotors are more reliable than single rotor platforms.” False. Multirotors are often presented as having more redundancy than a single rotor, due to having 6 or 8 propellers. The issue here is that each of these propellers have individual motors and speed controllers, each being a potential failure point. For example, each octocopter has 8 times more solder joints to potentially melt due to high resistance overheating compared to a single rotor. Some argue that should an octocopter lose one motor, control can still be maintained. While this is true, the problem is, that to carry a Red Epic size camera, the power systems are usually very near their operational limits, making recovery after losing a motor far less likely. A large single rotor platform can very easily carry a Red Epic in the most demanding climates without significantly taxing the power system. All of its mechanical components have evolved over decades of outright abuse to be very reliable. Another added bonus flying the single rotor heli is the ability to glide down safely by autorotation in the event of a main power failure.
4. “Multirotors can do anything a single rotor platform can.” False. Our latest single rotor platform called “BRUTUS” can easily lift a 30 lb. camera payload and fly it for 15 minutes. It also has a top speed of over 80 mph carrying a Red Epic (twice the speed of any multicopter). It can smoothly descend at a rate 5 times faster than a multirotor and can also provide usable footage in up to 25 mph winds safely. Multirotors are generally preferred when flying close to talent. We are now getting smooth footage from the Movi at 100mm’s so the heli can be flown at a safe distance from talent and still pull of tight shots. This rig is powerful enough to haul a Red Epic Dragon with anamorphic lens and FIZ witout breaking a sweat. Our industrial inspection division – Drones That Work in many cases prefers single rotor helicopters due to their improved productivity on large inspections, being able to descend much faster than any multirotor.
5. “A heavy lift multicopter costs the same as an equivalent single rotor platform.”False. At current pricing, an 800 size single rotor heli is approximately half the cost (both with GPS flight control) of a heavy lift multicopter with the same camera stabilizer/auxiliary components.
6. “Multirotors provide smoother footage compared to single rotor platforms.” True. Or at least this is true for most. Having said that, a highly skilled builder can balance a single rotor to be just as smooth but this level of skill is uncommon. The recent development of brushless gimbals like the Freefly MOVI MR also levels the playing field between both platforms ability to provide stable footage. We have recently discovered that we are able to run much higher stiffness settings on our MOVI flown on our single rotor rigs compared to the multicopter which is another very significant advantage. This is primarily due to the difference in vibration frequencies and mass distribution between the two arrangements. We have also discovered that in fast forward flight (> 25 mph) the single rotor helicopter provides much smoother footage, due to the greater vertical distance between the rotor disc and the camera mount along with the fact that most single rotor rigs have main blade axle damping which helps to absorb aerodynamic disturbances like wind gusts. On most multirotor rigs the propellers are rigidly mounted to the motor shaft which permits such disturbances to be directly transmitted to the airframe. Synchronization issues between multiple motors often results in unwanted vibrations that occur intermittently during flight. The Freefly Systems Alta uses a very novel solution by isolating the airframe and batteries from the airframe using a series of O-ring isolator cartridges of varying stiffness. Using a single motor rotorcraft alleviates this problem because the rotor system is designed with dampening of aerodynamic forces and vibration built in.
These comments should not be taken as being negative towards multirotors. We have and use both types of copters wherever they fit best. In rough terrain, it is awesome to be able to hand-launch and retrieve a multirotor for example. The Freefly Systems Alta can mount the camera in skyview for a very unique upward perspective. There is an increasing number of clients who are specifically requesting multirotors under the impression that they are always the better choice and single rotor platforms are less capable “old technology” which is incorrect. In the hands of a top-notch, world-class pilot, both platforms can be very safe and can provide breathtaking, dynamic camera movements. As mentioned before, as this industry goes forward, it will not be those that do things better that will win, it will be those that do things different. This is why we continue to develop, evolve and use single rotor aerial filming rigs.