AOS ul7
The latest version of this frame is the AOS UL7 EVO. It soft mounts the FPV Camera, supports ND filters with DJI O3 and fits 14-20mm FPV cams (14mm uses a 3D printed mount, STL provided below).
THE CHALLENGE
Learn about the challenges that led to the AOS UL7
Vibrations limit performance
As a pilot I often struggled with Jello, mid-throttle oscillations and propwash handling on my freestyle quads and this problem gets worse as the quad gets larger. Traditional 7 inch frames (especially those derived from 5 inch designs) struggle with oscillations, jello and tuning issues which are often impossible to fully resolve. As an aerothermal engineer I realized that the issue lay in the vibration and resonance performance of the quadcopter frame itself.
Even the cleanest motors and props produce large amounts of vibration in flight. These vibrations excite the resonant modes of the frame amplifying vibrations at certain frequencies, increasing their amplitude and energy. These vibrations pass into the gyro and create noise on the signal. This noise requires additional filtering and limits maximum PID gains through motor heating.
The result is a flight controller that is slower to respond to propwash and your stick inputs. The AOS UL7 takes an innovative approach to resolving these challenges.
THE DESIGN
Understand the design methodology behind the AOS UL7
Harmonic analysis is the key
I used Blackbox logging and harmonic analysis to visualize the vibrations of the AOS UL7 during the design process. This allowed me to tune the geometry of every part of the frame, moving the frame resonances up and away from the motor frequencies and separating them as far as possible. This avoids, as far as possible, the situation where the motor frequencies match a frame resonant frequency and so amplification is minimized.
As a result, you can run less filtering. Every layer of filtering adds delay that’s mathematically related to how effectively it removes vibrations. This delay prevents the flight controller from responding rapidly enough to propwash leading to poor propwash handling. Reducing the amount of filtering is the best way to improve propwash handling. With the AOS UL7 you’ll be in the best possible position to reduce your filtering to an absolute minimum.
Another advantage of lower noise is the ability to run higher PID gains. Higher PID gains allow the quad to track your stick movements with less delay and more precision. The result is greater confidence, particularly when flying tight lines where fast reactions are vital.
KEY FEATURES
See the key features of the frame
Top and bottom plates
Both of these plates are 2mm thick to provide an optimal balance between strength, stiffness and weight. The cut outs in the top and bottom plate of the AOS UL7 are tuned using finite element analysis to preserve as much of the bending and torsional stiffness of the plate as possible whilst minimizing weight.
There are mountings for three 30.5x30.5mm or 20x20mm stacks with plenty of space in between for the receiver, capacitor and other accessories.
There are also two hard mount points for SMA antenna connectors.
Arms
The AOS UL7 further develops on the truss design used for the Cine80 but takes it to the next level. Each arm is made from two vertical parts that interlock together. This allows both struts of the arm to be cut with the fibers aligned along the length of the part maximising the material stiffness and strength in every part of the arm.
The vertical truss design provides enormous stiffness per gram in all directions. Truss structures are inherently very strong as they convert bending loads into compression and tension in the individual members. Carbon is much stronger in pure tension and compression than in bending.
The motor mounting is easy to assemble with 3 long screws that go through spacers into press-nuts. The 19mm motor mounting supports 2808 and 2806.5 size motors which are ideal for 7 inch props.
Camera Protection
The AOS 7 uses 2 mm Carbon Plates to hold and protect the camera. These are stiffer, lighter and cheaper to replace than aluminum or titanium.
The camera plates include 2 standoffs to maximise durability and a cutout pattern that supports DJI O3 and all typical19 - 20 mm FPV cameras.
GoPro Mount and 3D Prints
The GoPro mounting pattern on the AOS UL7 is identical to the AOS 5 and AOS 5.5 so any mount designed for any of these frames will fit and work perfectly on the others.
The GoPro is secured by 4x M3 screws so you can be confident that the mount will not be going anywhere in a hurry.