https://www.youtube.com/watch?v=wV4Y40fs4is
A first hand hand account, by our 17 year old High School Student: Gustavo De Leon-
"I go to a school in Southern California called High Tech High Chula Vista, and as part of our junior year academic requirements we are asked to participate in a month long academic internship. That way we can gain valuable real world work experience and to get a chance to see if our career goals are something we really want to commit to, or perhaps something we only liked in theory. I was lucky enough to secure an internship with 3D Robotics at their engineering offices in San Diego where I spent the last month working from 9am to 6pm.
My first project was to build an old quadcopter, something which I was told should take about a week, but instead I finished building it in the morning of my second day. It took another day or so to set it up with Mission Planner, and it wasn't until that Friday that I was able to go out and fly it, but I was off to a pretty fun start. I spent the next three weeks doing a little bit of everything. We spent a few days organizing the Flight Ops area, another week or so installing Go Pros and LEDs on X8s, and replacing autopilots and GPS units and diagnosing any issues.
My free time was spent on an abandoned project from a year ago, a one of a kind copter with eight arms and sixteen motors (in the X8 style). It took quite a bit of work to get going, including soldering a power module into the existing power connectors, but I was finally able to get flying on the final day of my internship.
My free time was spent on an abandoned project from a year ago, a one of a kind copter with eight arms and sixteen motors (in the X8 style). It took quite a bit of work to get going, including soldering a power module into the existing power connectors, but I was finally able to get flying on the final day of my internship.
All in all, it's been a fantastic experience, and I am not particularly looking forward to going back to school next week."
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If you are interested in an internship with 3DR,
keep an eye out on our Careers page: http://3drobotics.com/careers/
Comments
@Leonard:
The stability in the wind with flat vs coax is mostly from personal experience, haven't found a good explanation of why yet as far as I'm concerned it is still subjective to the user and tuning like you said.
The better view for a camera is a flat hex vs Y6, flat octo vs X8. The tri's and quads are not redundant but are otherwise actually better in this regard because of the absence of the lower rotors.
When I say easier to maintain orientation I mean hex vs Y6, flat octo vs X8. I am comparing vehicles with the same motor count in a flat vs coax arrangement.
@Rob
To add to what you said,
Totally agree on the approach to building an aircraft based on mission requirements. We have so many selections of props and motors now, we have the option to make a very efficient aircraft built for a specific task. A flat configuration is almost always more efficient, but that is only important if efficiency is your top priority. Transportation can be a major factor in the design requirements that may favor a coax setup. The disk area is key to efficiency, which is why a very efficient traditional helicopter is probably more efficient than the equivalently sized efficiency built multirotor.
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The reason the X16 exists, is because I wanted to show everyone a side by side comparison of how small an X8 with 10" props was compared to a flat octo with clearance for 10" props. The guys in TJ thought it would be fun to make it a coax, and that is how it showed up on my desk. Challenge accepted! The physical size of the X8 is much smaller, and has the ability to run much larger props, therefor becoming more efficient for it's size like Rob said.
@Hugues
It is wired like an X8 but in parallel. No modification to the code is needed. Look at the prop directions in the photo, blue arms are the two inner front arms. As long as the number of motors on the vehicle is in multiples of 4, 6 or 8, coax or not, you can fly it with the stock code. The X16 should is probably better named the X8 2P. If you decide to build one, make sure to label your cables! Otherwise you will spend 90% of your build time tracing wires.
Can you explain how you configured 16 motors: two parallel flat octos? Rotation direction of motors on same arm?
Did you modify APM to manage this config?
Yes, I agree.
The main point I was trying to make was slaying this sacred cow that Coax copters are 30% less efficient than singles. That statement is used very commonly in this hobby, but it's only true in a very limited set of circumstances. Those circumstances would be "Hey, I bought these motors, what can I build with them?" And that's a very strange way to engineer an aircraft.
It's kind of the same way that Canada has run it's fighter jet procurement program. "Hey, the Americans designed this cool looking F-35 that we really want to buy. How can we redefine our mission requirements to make it the only acceptable choice?" ;)
I agree Rob,
but you are talking more about a disk area vs geometrical area of the frame than the comparison between single disk and coax setups. If you uses a quad on the left frame instead of a coax setup you would get maximum 5% less efficiency (but only if you got the coax design perfect), but less weight at the cost of redundancy. If it wasn't for your redundancy requirement, you could make the same argument comparing an octo and quad.
The idea that a coaxial setup is always less efficient than a flat setup is only accurate when you design your machines backwards, as most people do.
Most people choose their motors and props first, and then ask "Will these be more efficient arranged in a flat pattern, or coaxial?" That's not how aircraft should actually be designed.
If you start from the ground up, you might consider the problem more like: "I have a 1 kg payload, and I need 8 motors for redundancy, and I need my machine to fit in a certain space for storage and transport. How can I achieve the best efficiency?" If you were to do this, then you'd realize that X8 is more efficient. Consider these two machines, with exactly the same frame dimensions. One is an X8, the other a flat Octo. The X8 has 24" props, and 1.168m2 of single-layer disk area. The flat Octo can only fit 14" props, and resultant 0.7693m2 single-layer disk area.
As you can see, the flat octo is clearly a less geometrically efficient layout for a multirotor. The X8 will be more efficient, and be even easier to pack than the flat Octo even though they have the same motor dimensions.
Thanks for posting your reference here Joseph.
For those that can't be bothered reading the paper the basic improvement Joseph is referring comparing a coaxial rotor with a single rotor with the same "solidity". The paper explains that a pair of coaxial propellers, with two blades each, can be optimized to achieve approximately a 5% improvement over a single propeller with 4 blades (to keep the solidity equal) and the same diameter.
This is often confused with comparing a pair of coaxial propellers with the same propellers side by side for example an x8 vs an octo. In this case I have seen no example in the literature stating the coaxial configuration can be made remotely as efficient as two independent rotor disks. This is because the coaxial configuration has almost half the area as the two independent rotors.
So the quick summary, an Octo is always more efficient than a X8 and a Hex is always more efficient than a Y6. (assuming well designed examples with the same or similar props).
Joseph does make a couple of other points.
The first is arm weight. He is completely correct here. The arm weight is halved so a 3dr Y6 will save around 150g when compared to the old 3dr hex. Not much of a dent on the 20 to 30 % efficiency hit but it helps.
"Coaxial setups are more stable" Sorry but I have to disagree with you here. I think this is a myth based on experiences of people moving from a small quad to a larger and heavier hex. I also think that the average person propagating this myth has relatively poor pid tuning skills. In my experience the coaxial configurations don't handle as well.
"Redundancy of power systems" This is defiantly true for the Y6/hex and true but marginal for the X8/Octo.
"Better view for the camera" This is only true for a fpv style camera on a Y6 vs a Hex. The Y6 has no advantage over a Tri here.
"Smaller/Easier to transport" Yeh, I agree with that.
"Easier to maintain visual orientation" This is the same as the camera point. It isn't the coaxial configuration that does this. The Y6 is as easy to orientate as a Tri and the X8 is as easy as a Quad.
@Jack: Yeh, I am tired of this talking about this too but what can you do.... I will say my personal camera ship design is a Y6 with folding arms. The flight time and control quality takes a hit but I am willing to suffer that for the redundancy and easy folding for transport. My primary use for this is filming while 4WDing. I have lost one gopro and I don't want to loose another :) (or the copter).
And well done Gustavo De Leon!!! I am glad you learnt a lot and enjoyed your time at 3DR.
@Jack: Theoretically, from a purely aerodynamic perspective, a coaxial configuration can be engineered to be slightly more efficient than a single disk according to NASA http://www.rcgroups.com/forums/attachment.php?attachmentid=2815698
Now, in practical applications with a multirotor aircraft, consider that the weight of the arms required to produce that thrust is now reduced by 50%, because there are two motors per arm instead of a 1:1 ratio. Even if the drawback was large with a poorly designed coax setup, you're only going to see a small difference in flight time.
Some other benefits:
-Coaxial setups are more stable in the wind then the equal motor number flat arrangement equivalent
-Redundancy of power systems
-Better view for the camera (if that is the payload)
-Smaller/Easier to transport
-Easier to maintain visual orientation.
Lastly, there is no such thing as an age limit on hiring.
@mP1: That issue is not one I am personally involved with, but I do know that it is being addressed in full force and is a top priority right now. My advice: Be patient as it will resolve as soon as realistically possible.
This is a story, but there are no announcements about international shipping being stopped or restarted ? All those international customers both past and future would be glad to know there arent bigger issues to worry about.
It's a lot more interesting, coming from nothing to building anything for a living. Someone who already knew vertically stacked propellers were drastically less efficient than horizontally spaced propellers would find it torture to build these vertically stacked copters & engage in a complete debate of the rationale, stacked propellers vs. ducted fans, shrouds vs. open propellers instead of just doing their job. It might explain the age limit on hiring.
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