what size multicopter for AP/AV ?
well, It seem like I've been getting this question asked a lot recently with release of my new AP/AV multicopter frames. So I want to spend some time today to discuss the consideration for deciding what size multicopter frame to choose.
When I began my multicopter journey, I started out with spectrolution board. it was first "Affordable" controller at mere 450 bucks and came with 3 axis of gyro and thermal levelling system (similar to fma copilot . OMM (oldmanmike) was using small outrunners with 10" epp props and I was one of the first to use dt700/750 in multicopters. Since we were mostly doing still photos and crude video, the airframe was very simple and crude by today's standard.
fast forward 4 years and now, multicopters have become ubiquitous. With all the variety of choices, it has become more confusing to choose, so I wanted to share some basic criteria.
Much as Hexacopter has been popular in US (this due to certain reasons that has to do with availability of small motor and props more than anything) we find coaxial type of multi does much better in windy situation. In general, quad is no worse than hexa in most cases and cheaper. While lightely loaded hexa will offer some protection against motor outage, this is rarely the case in AP. Also in general, bigger disk area means worse wind performance. That is why we have settled on quad, y6 and x8(both coaxial) form of multi as being ideally suited. Coaxial multicopters also tend to have best neutral flight behavior, but their downside is loss of efficiency . For many AP/AVers, we would gladly trade the efficiency for flight behavior that brings us the result.
Lets talk about classes of multi:
1) 1kg multi like the new DJI phantom or F330. The compact sized, able to fly on 3S 2200 pack and able to carry a gopro, this class is ideal for portable, quick and dirty FPV and AV setup. Very affordable and still capable with gopro H3. Small area multi, but not very good in wind. biggest benefit is safety. small props and small size naturally makes them much safer around people. typically 8" prop or smaller running on 3S2200 pack.
2) 2kg class is very important in our opinion. with FAA 2kg /license free uav for first responder, we feel that future will be sub 2kg class multi for everyone. We can't stress safety enough. If you notice, we have always pushed the envelope of smaller size. With the new Crab quad and AV500 with either Gopro H3 or RX100, we feel that we can come very close to 2kg. it will still take careful selection of component to get there. typically 10" prop and runs 4S3000 pack . 2212 to 2216motors.
3) 3kg class. This is where our shrimp fits in. This class allows compact size Y6 with full sensor camera like Nex5 and GF3. I've had my shrimp down to about 2.6kg fully loaded, but they usually come in 2.8kg ready to fly. still under 3kg with full load and FPV gear. Personally, I really like this size. I love the way Y6 flies and everyone that has flown my shrimp really comments on how stable and honest it is. I run 9" prop, but most will run 10". 4S5000 to 5800 pack for 6-7min flight time. 2216sized motors.
4) 4kg class. This is where our lobster fits in. very popular and still small enough for smaller pack.. you can actually lift DSLR on this size or sony camcorders. larger is bit more stable and bit easier to see. requires 2814 or pancake motor and run 11 to 13" props. (or bigger) 4S6000 pack seems to offer about 6-7min flight.
Fllight time: We really target 6-7min with 20% reserve. we feel that give enough flight time for most jobs. The key to long flight time is in building light and using bigger prop with matched pancake motor. In general, Y6 is going to lose 10-15% flight time vs hexa as well. It is possible to get 15+min in optimized setup like the S800. We do feel that with good optimized setup. 8min with 20% reserve is possible even with shrimp/lobster. (shrimp with smaller pancake running 12" for example)
Prop choices: For us, choice is either graupners or wooden props like the zingers. I know that Xoar also has a following. In anycase, we find that Woodies really do work well for AP/AV, even though they usually are bit less efficient. We love the safety aspect of wooden props. Unlike Plastic, they rarely cut, but break. We've seen all the horror picture of prop cut from plastic ones. The other benefit is that they usually perform better in wind. Downside is efficiency. Compared to SF props, it will be less efficient. It is our theory that it is this inefficiency that allows the fcp to be run at higher P, which gives us bit more stability. For plastic props, graupners are hard to beat. but they do cost .
motor choices: we really need to test more small pancakes. currently though 2216-800 really is the choice for smaller multi while 2814 is popular for larger multi. we really do like hengli pancake and we are ready to do more testing on 3508 sunnysky as well.
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