Various UAVs were on display at the 2014 Security & Policing Event, 11 - 13 March in Farnborough, UK.
The exhibition featured a Live Demonstration Zone, allowing exhibitors to present their equipment to the audience.
Below a few UAVs showcased at the event:
COBHAM Surveillance UAV
aerovironment Qube
aerovironment Puma AE, Raven and Wasp AE
Altura Zenith ATX8
www.diesunddas.co.uk
Comments
No...wind "see"your props as a flat disc surface witch is much bigger on flat octa,I hope you understand me bcs my English is not the best one...
and yes,coax is less efficien for sure,how much,who can tell exactly I don't know
for me,simplicity of a quad is best....
i am taling about this x8 quad its got 8 arms, so he same weight as a *8 it has efficiency loss from being coax, it has efficiency loss from the arm covering the top and bottom of one prop and the top of the other, It is simply less efficient, also it is the same surface area, you realise ther is still 8 props, the surface area doesn't magically vanish because the arms did.
I forgot to mention x8 ory6 frame is better in windy days as well..not just bcs of stronger airflow under 2 motors but also it have less surface wind hits...so,it will always be + and - depends for what as someone said before
have to post another video from Warthox...he is unreal....
https://vimeo.com/32408610
and yes I know police wont fly like that but just hoover...
https://vimeo.com/17756183
Jared...I also have to disagree with you
1.coaxial is better solution in redundancy especially X8
2.x8 and flat octa cant be same weight,you did some bad design if they are
3.25% loss?!no,my experience tells me its only around 10-15% loss
4.only 25% more power its maybe best for motor efficiency,but for sure not for redundancy
5.statement that you continue to fly with one motor failure like nothing happened is rediculous
6.multirotors can fly "zigzagging" and be agile,it also depends of your flying skills just check test video with flips with big Kraken 130 form foxtech
https://www.youtube.com/watch?v=4lyN-1SOdsA
or legendary Warthox videos zig zaging,this is extreme example ofcourse..I am sure he can demonstrate with big X8 as well,I don't have time to find it
https://vimeo.com/72441236
I do agree nothing revolutionary in given examples...best one for me is aerovironment Qube...
no hard feelings just my opinion ...
I have to disagree some carbon fiber arms are so light they may as well not exist, coaxial is a less effective solution in redundancy / weight as you have to rely entirely on the paired motor if one fails which means that those motors need to be overpowered which means less efficient which means lower flight times.
you want to make the copter have only about 25% more power than is required for the desired flight characteristics otherwise you are over specking the system and wasting power like a 4litre car engine doing 30mph commutes.
IF one motor were to fail in a properly calibrated system you would find severe limitations in flight performance you may have to simply land and recover it whereas properly calibrated octos with a single motor failure can continue to fly as if nothing has happened.
I know this from first hand experience when building both designs, i used identical power setup they weighed almost the same but with the coax octo when one motor artificially failed it had a seriously hard time maintaining stable flight whereas with the octo traditional with the setup i talked about, i did not even realize a motor had lost a prop from a loose fitting until i landed after a 20 minute flight, i only noticed a slight torque effect when ascending.
Raising the motors above CG is useful for slow,fast and still flight, it also reduces instability in free fall and it keeps the copter upright allowing for faster decent.
There copters are designed to fly as the crow flies or hover, they are not for zigg zagging which is agility
If they wanted agility the prop sizes would be smaller.
but these have huge props with low KV motors to achieve long flight duration which by definition reduces agility.
the fact of the matter is a traditional octo is far more efficient than the equivalent coaxial version, the added weight of an arm is so insignificant.
I will agree on compact designs, you cannot be as compact as the coax version but most of those designs have plenty of space for extra motors without extending the arms.
Coaxial rotors aren't really that bad. You can get the aerodynamic efficiency lose down to 8% and more than make up for it with reduced weight and more durable structure having only four short arms, versus eight longer arms. Having a compact package can be of use for easier storage and travel, usually in the trunk. Problem is most hobbyists don't know how to optimize a coax setup, or get the most gain from it, but they sure do know how to come to the internet and complain about how bad it is, lol.
The props should be at the same Z axis height as the CG of the multirotor... raising it or lowering it doesn't affect stability in a positive way. It'll always rotate around its CG, so the question is would you want your rotors going up/down or swooshing sideways through the air as you pitch and roll? :)
I worked with a ex employee of a company who had been contracted to do research into efficient designs ( i was asked not to say his name or company because of secrets ;), he explained the results and there are many things you can do to improve efficiency, i do not see any of these guys including all the very basic efficient design modifications.
it just looks like they didn't really try.
eg: raising the props above the central mass by 5cm hugely increases level flight stability.
giving the motor a 10degree tilt so the blow outwards slightly will increase ascending and descending stability reducing the toiletbowling which is cause by the copter traveling through its own prop wash.
it also allow greater horizontal speed by allowing you to tilt over 45degrees without loosing altitude.
under mounting the motors gives 5 to 9% efficiency increase as you do not get prop wash from air flow hitting the arm or loss of power. you get a very partial vacuum instead.
do not enclose traditional blades as they have done either as you can loose up to 14% efficieny from a vaccume forming on the tips of the props where you would usually get the majority of your lift from.
I am no expert but i do have far to much time on my hands and the sheer amount of multirotors i have built with drastically different designs has helped me far more than speculating or simulating could.
I adore this hobby itis my life and the result it obsessive dedication :) hehe
these are basic design modifications that give a much more stable and efficient craft as a result.
another reaso stacked designs are bad comes down to redundancy, a dual quad design will have to rely 100% on the motor that is closest to the failed motor but in a traditional star design the failure gets shared between two motors
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