Hexacrafter.com HexaCrafter Frame Strength & Design- The Explanation

[Hexacrafter]

HexaCrafter Frame Strength- The Explanation
Over the last couple years, we have been asked many questions about our frame design as it is unique. The HexaCrafter airframes were designed using computer assisted structural design modeling to obtain the strongest possible arm, arm to frame & arm to motor mount systems.
The arms are rectangular. This is by design. For those familiar with structural shapes, the rectangular tube and I-Beam are the "go to" shapes for structural engineers. These shapes produce the minimum deflection and maximum strength by cross section of materials. The rectangular tube further was chosen as it allows for "simple" component connections with maximum strength. Take the time to "look up" the next time you are at Home Depot, Lowes, or any other building with exposed structure. The main beams spanning the columns are rectangular steel tubes most of the time. Have you ever seen a "Round" steel beam spanning the columns?
Many have commented about a "round" arm being better for aerodynamics. We respond by saying that on a Multicopter, Nothing is aerodynamic. Add a large 3-axis gimbal hanging below and the concept of aerodynamics is completely moot. The custom fabricated rectangular arm tubes we use have radiused corners. Eliminating the "sharp" corners assists with aerodynamics, but we have not been able to see any significant thrust loss or resistance in our rectangular tube design as compared with other Multicopter arm designs. Square arms have been used for multicopters by many DIY & competitor frames from the beginning of multicopters for the strength & connection advantages.
We have designed continuous internal bolted connection construction for all arm to frame & arm to motor mount connections. This connection is the strongest connection we were able to model & test. Additionally, three bolts are used at each connection to provide "triangulation" for maximum strength and shearing forces.
Over the last two years our frames have survived devastating aircraft crashes with minimal or no damage. This was also a main goal in our design. As of this date, no client has broken an arm, main frame or arm connection in major crashes that would most likely been devastating to many competitor airframes.
I know that this posting will most likely "stir" the pot of controversy over frame designs, arm shapes, aerodynamics, but our frames have proven themselves over and over for frame strength, minimal deflection, durability & flexibility of design for 2 years. We are very proud of our design as it has accomplished it's goal....Extremely durable, lightweight, easily serviceable, and priced below our big name competitors.
Please view the video of frame strength:

I hope that some of our clients who have experienced our frame strength first hand will post their experiences and share them with the Forum. We have received many amazing reports of accident survival from our clients.
Thanks again to the Forum for allowing us share our design & opinions.
Andrew Raines

 

[Bartman]

Hi Andy,

Regarding aerodynamics, the arms are in an airflow below the propellers where drag across the arm is a factor as that drag and the turbulence around the arm contribute to airframe vibration and efficiency. Have you ever seen airflow over a rectangle? Round shapes aren't perfect and are actually about four times more draggy then a streamlined cross section but they do fall above rectangles on the drag charts. And fwiw, the beams I've seen are either a welded truss assembly (ceiling joists) or I beams (column to column beams). As a mechanical engineer I happen to look up at stuff like that.

Regarding impact tolerance, I'm interested in having my motors and stuff survive so if the frame can give a little in the impact and even break to keep the motors from being bent to hell then that would be a good outcome.

I've seen your products and they're nicely designed and you present everything in a very professional way so I'm sure your customers are happy with their purchases.

Bart

 

[Giovanni59]

An excellent design, proven over and over again

Andrew, That's a great explanation of the design philosophy behind your product. I am one of those who will testify to the durability of these frames, I own three of them now. Two have met devastating crashes and it was only the landing gear that got damaged and this too is by design. The impact energy is translated to relatively cheap replacement parts. This is similar to Bart's point of having something to absorb the energy but any crash that can impact so greatly on the airframe would probably render the motors damaged in other ways and one wouldn't want to risk using them again. At least I wouldn't from what I have learned in the past few years. As to turbulence from the airflow hitting the arms, well all I can say is these Hexacrafter frames perform beautifully. If there is any turbulence that is effecting performance I would ask anyone who claims that to show how it is doing so. These craft fly very steadily and that performance is attributed to the rectangular shape of the arms that makes them so strong as well as flex free. The very design that Bart claims will make the frame shake is the very factor that keeps them from doing so. John

 

[Hexacrafter]

Just a quick reply.
Please see image below. The square or rectangular shape provides 1.7 - 2X the strength that of a round, but the airflow issue is not as severe as many believe. With rounded corners, the rectangular is slightly less efficient aerodynamically than the round, but with great advantages in tube strength & connection strength.
View attachment 15166
I knew before posting my test that many would use the "airflow" challenge. I will agree that rectangular is less efficient with the thrust vector, but personally feel that the trade off with strength & durability is worth any stated losses. We have done extensive testing and cannot find any loss of lift or vibrations related to the arm shape in our aircraft.
This is the great part of our "hobby". There are many different approaches in frames and motor configurations and many will have opinions about which are more efficient/ less efficient/ stronger or weaker and sometimes it is simply a matter of what is the important aspect of the design that works for the user. Our approach is strength, durability with very stable & smooth flying aircraft.
Thanks again to the forum for providing this platform to present our products & ideas.
Andrew
PS- I also wish to note that we had considered offering an oval shaped nacelle that would mount to the top of the booms creating a squoval shape if needed, but have not received one complaint to date necessitating the offering.