Hi there friendly people of DIY Drones
I've been using and building drones for a few years now, and general shortcomings, I find are: noise, flight time, payload capacity, waterproof space for sensor and computing additions. These shortcomings of course all have good reasons to be there.
Some of the things I've done in the past are: made a really big rig (2m span) that's capable of ~1hr hover, and a few kg's payload; made some smaller rigs with some interesting technologies such as vertical surface extended docking (windows/walls). After a whole lot of effort and various iterations, myself and fellow collaborators at Crimson UAV have come up with the Talon6UAV. It is designed to be a premier aerial photography, survey, and R&D drone.
Some of the key aspects are:
Quiet Operation: Large 26" carbon props operated by high torque motors in an alternating overlapping pattern enables a stable and quiet flight
Endurance: Lightweight and elegant design coupled with up to 888Wh of battery capacity enable long flights ~40minutes
Low Downtime: A rail and car battery changing system enables seamless no nonsense battery swaps to keep your business in the air
Development: Dedicated waterproof space and power supplies for companion computers and sensing equipment allow this craft to be quickly modified to your needs.
I would really appreciate any feedback, thoughts or ideas from all the knowledgeable people here.
The aircraft page can be seen at Crimson UAV
Comments
Yes, Simon - the concept in your video is intriguing.
But given the weight of theory it seems to contradict (as noted in the thread I posted), it's 'a bit thin', if I may say so. (the first flight, for example, seems to get barely off the ground, and lasts a few seconds, unless I'm receiving the video wrongly).
More data are needed.
And sure, I think we all understand X8s (co-axials in general) are significantly less efficient than separated props.
My reading of Rob's post seemed to suggest they were as much as 50% less efficient, and I've just never seen numbers that high.
George
When a multi-copter flies forwards the amps are reduced, a Multi-copter is less efficient in hover.
Using such large props comes with more problems, the hardest part is slowing the props down, with such size and mass of the prop. Stabilisation is reduced. Multi-copters perform best when the esc's can speed up AND slow the prop quickly.
Also having a prop on the bottom is less efficient than the top, X8 copters are even less efficient.
We have been through this before, time and time again.. I even made a simple video a couple of years ago demonstrating this...
https://vimeo.com/84825842
I have flown for 90 minutes using 28inch props, however in winds over 10 knots the copters flight characteristics were poor, the props just can't spin fast enough, using a higher voltage pack helps but the problem still remains.
Have fun!! :-)
Simon
Sure, Jason, I'm aware of Translational Lift - helicopters are more efficient in forward flight due to 'clean air'.
I'm not aware of any reason this applies to helicopters but not multi-rotors. I doubt there is such a reason, but perhaps (maybe multi-rotors only gain the translational lift on the forward-facing props, and not the back ones?).
And all rotorcraft work harder to stay tilted (assuming they don't wish to lose altitude). Basic physics of thrust vectoring. Again, no reason (that I'm aware of) that helicopters get any special benefit here.
Helicopters, indeed, possess major advantages. Imo, especially endurance (because gas), and doubly-especially, wind-resistance (because variable pitch).
Interesting to see Rob considers them better only for some applications (I had assumed he was a hard-core 'helicopter guy').
George
George Kelly
https://en.wikipedia.org/wiki/Transverse_flow_effect
A helicopter gains efficiency when it's moving due to transverse flow effect, essentially it's moving into new air and producing more lift from the forward motion and clean air it's going into.
A multirotor is the opposite, as it moves it has to use a lot of power to keep it tilted and essentially keep it at a banked angle for movement, this is incredibly inefficient.
For any movement/mapping application a helicopter is far better, not only is it more efficient, safer, and more stable, the sensor is not tilted as much as the heli does not need to tilt nearly as much as a multirotor to move the same speed.
Quads are great for toys, small fpv racing, and still applications where there is no movement, but, for actual mapping or commercial use beyond a flying camera in one place, a heli is far better suited.
This thread includes the, admittedly heterodox, claim that bottom-mounted props lose 5-10% efficiency:
http://diydrones.com/profiles/blog/show?id=705844%3ABlogPost%3A1537...
Thread petered out without resolution.
Has the OP tested this ?
(though it certainly simplifies overlapping of props)
George
'A coaxial X8 octocopter as the same disk area as a quadcopter with the same propellers... An X8 is like a quad with the motors cut in half'.
Rob, are you saying the efficiency penalty for an X8 is 50%? (no increase in disk area by adding 4 more props of same size).
George
'The point is a helicopter is even more efficient in motion, aka, doing work, while a multirotor is considerably less efficient when it's moving or mapping.'
Why?
George
Overlapping props is not a new idea, but in fact it does not do what people think it will do. We also tried it about a year ago (trying to increase lifting power while retain same small span). We did not get the thrust we expected.
We actually performed some experiments. Set HK prop dynamometer (thrust meter) with one prop and another motor with prop overlapping the measured one. When one prop rotates we got full specified thrust, when we turn on second prop (overlapping rotation in the same direction as in your Talon) we got 25% decrease of the thrust. Exactly equal to the percentage of overlapping area.
Props generate thrust by accelerating molecules in air in opposite direction (slightly on the sideway) and when the wing of the second prop (under) passes through its wash it has nothing to accelerate. It essentially moves without interaction with air ans do not generate thrust.
The solution is opposite rotation. As it is done in coaxial props.
If you reverse rotation of your bottom props (reverse props also) you will get probably 10 to 15% of more thrust. Hard to estimate your overlapping from pictures).
Would be interesting to see your results.
Cheers!
Ah yes, my mistake ... (Re: arm folding sideways). Nice!
@Rob: Agree. Umbrella folding typically leads to vertical storage, more cumbersome.
@RPM the 2 cf tees are there for if you want to put payloads on top, they also make it quite a bit easier to put the aircraft upside down, and work on the underside (say if you're installing a companion computer, or wiring in your payloads), and yea inverted landings jk :D !
@Rob I'm honored to have your feedback. I'll probably actually try to get a side by side video for a sound comparison, I know that buzz saw sound, and yea, this one sounds pretty darn nice to the ears (more like a low pitched hum). We're located in Vancouver, Canada.
@Batog Hey there, that's a very good question, and Rob answered it superbly.
@Olivier Hey there, thanks! I agree portability is super important. The arms actually fold sideways (Thanks Rob!), [ Olivier, watch near the end of the video on the website to see this], I think it's decently portable, and I've been transporting this bird allover the place in the back of my car.
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