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Old June 2nd, 2012, 08:55 PM   #1
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Aerials Info: Multi-Rotor platform gotcha

I've been away much too long from this place and haven't responded to one question emailed me in... geez, since Moses was a boy.

But one poignant question was sent to me that's been haunting me, and that's the people who are considering getting into RPV / RC-heli aerials, specifically regarding the "new" multi-rotor / Quad-Rotor helis that are gaining traction in the marketplace.

First an update to something posted a few years ago about the potential threat from the FAA about using RC-helis for commercial work: The Fed's finally laid into place new legislation that specifically allows this type of use in a wide swath. It's not a perfect setup but the specter of someone from the FAA shutting you down (as happened to a few companies just a few years ago) is now gone. So about those multi-rotor aircraft...

The biggest problem with RC-based aerials is nearly everyone who tries it comes at it from a hobbyist perspective, meaning, they approach the aircraft, radio setups and most especially flying techniques from the same mentality as those who simply fly for fun. Which is logical because the concept of using RC aircraft for professional aerials obviously originated and is evolving from the hobbyist industry.

But if your goal is to make money from this venture then you really need the perspective that the RC version of your heli is in point of fact a miniature full-scale aircraft, and consider the flying, setups and safety concerns similarly.

To wit, any multi-rotor helicopter regardless how large or how many rotors it uses has one major and potentially fatal flaw: It has absolutely no way to auto-rotate.

Auto-rotation in a helicopter is where there's either an engine/motor failure and if you're high enough and/or moving forward fast enough you can use the remaining energy in the main rotor to quickly - and controllably land the aircraft without crashing. Of course this maneuver takes practice and a deep understanding of helicopter aerodynamics and flight characteristics, but it can be done even in an RC helicopter with a *traditional* main/tail rotor setup. Here's the Wiki definition of how auto-rotation works:

"At the instant of engine failure, the main rotor blades are producing lift and thrust from their angle of attack and velocity. By immediately lowering collective pitch, which must be done in case of an engine failure, the pilot reduces lift and drag and the helicopter begins an immediate descent, producing an upward flow of air through the rotor system. This upward flow of air through the rotor provides sufficient thrust to maintain rotor rpm throughout the descent. Since the tail rotor is driven by the main rotor transmission during autorotation, heading control is maintained as in normal flight. However, as noted above, there is virtually no torque generated during autorotation, so to maintain flight in a straight line the pilot must keep one anti-torque pedal pressed to eliminate the tail rotor's anti-torque thrust."

There are a few reasons multi-rotor helis can't autorotate:

1. You do not control PITCH on the blades of a multi-rotor heli, only the speed they spin. No pitch control, no auto-rotation capability.

2. The blades on multi-rotor helis are so small they cannot produce enough centrifugal force in a fast decent to even be usable in a powered-off state, they will simply windmill slowly but not generate usable lift.

3. Because multi-rotor helis send power to all rotors at the same time they do not have a utility (so far) in which if one motor fails that the remaining units will spin up faster and, redirect inputs from the pilot to compensate the directional movement from the now missing dead motor. If you lose even a single motor you are coming down in an out-of-control state and with the speed of a homesick brick. Period.

That means you'll have ZERO control over it's direction of travel and how fast you're coming down. And if there are bystanders anywhere near the heli they could be in danger of being hit with life threatening consequences. Imagine a multi-bladed machine falling on top of you at 40+ mph. Not good.

There are a few more things that prevent auto-rotation in a MR heli, but these points above are plenty.

There are other non-safety reasons an MR heli isn't an ideal option:

1. They don't have the lifting capacity of traditional helis, which means only lighter, smaller cameras can go on-board.

2. Since they use multiple motors and blades that means you've increased the number of mechanical devices that can fail. (Consider that one of the main reasons Boeing and Airbus have dominated 90% percent of their commercial aircraft designs with only 2 engines is the same reason: Fewer parts to potentially fail/manage.)

3. Despite claims by the manufacturers MR helis are more susceptible to wind gusts and changes of air-mass direction so they tend to be more bouncy and "tweaky" in flight.

4. Because MR helis look nearly exactly the same from any angle you can easily lose the front-moving orientation of the aircraft while in flight, especially if you look away for a split second. That could be dangerously confusing especially with the "control reversal" that occurs with RC flight when the aircraft goes from moving away from you to moving towards you.

If you're considering RC-heli aerials then a traditional heli platform is what you want, for all the reasons above and more. Tried and true platforms are:

- Minicopter Joker / Maxi Joker 2 or 3
- Minicopter Diablo
- Align Trex 500 - 700 versions
- Gaui x7

And whatever you do, get with an experienced heli pilot that can teach you how to auto-rotate!!
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Old June 3rd, 2012, 12:02 AM   #2
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Re: Aerials Info: Multi-Rotor platform gotcha

Hey Robert!
While I agree with most of what you have pointed out, I will say the more serious multi rotor camera platforms use 6 or more motors with rather sophisticated computer control. They essentially have a "fly-by-wire" setup which compensates for a lot of the inherit instability of the system. They are much more stable than the 4 rotor and can carry quite a load. DSLR's and small semi pro cameras are no problem. I would never fly a more expensive camera on a 4 rotor for many of the reasons you mention. Six rotor...sure! Auto pilot hover and basic autonomous systems are out there as well. I spoke to a few companies at the last big event I attended and they said that even larger multi rotor systems are going to be available soon. It's really down to who want to put bigger motors and batteries together. I have one plane in which the electric motor system is outputting about 15 lbs of thrust. 6 of those motors would easily lift just about every camera out there. BUT just the motors would be over $1300. Probably another $1k for batteries.

For the newbie flyer they are a much easier platform to learn than a traditional heli. That said, I would recommend professional instruction on any RC flying machine if it's going to be used for filming...even at the hobby level.

The real issue with traditional heli's is the learning curve. Yes, they auto but even for experienced pilots an unintentional auto causes panic. Add the weight of a camera system and the benefit of being able to auto successfully is greatly diminished. The other more serious issue video-wise is being able to fly smoothly enough to get good footage. That can take years of practice...with the camera mounted. Heli's take on a whole different set of flying characteristics with weight added.

I think the best solution for starting aerial video and photos is the blimp. The small ones are typically seen at indoor sporting events and are around 10'. They can grow as big as you can afford and I've seen a 30' that had a full size shoulder mount camcorder on a 3 axis gimbal mounted to it! There's one I'm seriously looking at that will fly 30 mph! More than enough to make some really cool shots!

I've flown RC (all types) for over 20 years and have competed as well as been an AMA instructor. I have flown cameras for many years and have lately been playing with the Replay cameras on my heli's and large airplanes with pretty decent success but just for fun. They are still not up to my standards for professional use.
Even with the flying experience, I think my next venture may be a blimp.
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Robert Turchick is offline   Reply With Quote
Old June 28th, 2012, 08:54 PM   #3
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Re: Aerials Info: Multi-Rotor platform gotcha

Hey guys,

Whats a good RC chopper for a DSLR (7D or 5D) video shooting?

Looking for something under $1000 if possible.
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Old June 28th, 2012, 08:59 PM   #4
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Re: Aerials Info: Multi-Rotor platform gotcha

A setup that will lift a dSLR starts at about $5k and that is if you buy a kit and build it yourself.

If you are looking for a ready-to-fly setup expect to pay $10-12k.

What you are asking for doesn't exist in the sub $1k range.
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Old June 28th, 2012, 09:08 PM   #5
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Re: Aerials Info: Multi-Rotor platform gotcha

What about somethng for a smaller camera like a go pro? Or renting? are these available for renting?
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Old June 28th, 2012, 09:16 PM   #6
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Re: Aerials Info: Multi-Rotor platform gotcha

Flying a gopro gets you down in the $1500-2500 range.

I doubt you will find anyone renting one without an operator. Lots of liability there.
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