|Jul 03, 2012, 04:32 PM|
well, I get a lot of queries about various things related to AP/AV as well as multicopter, so I decided to distill it down to this entry. In realtiy, the answer is TANSTAFL. So, that is the theme of this blog. If you are a reader of Robert Heinlein, you will recognize this term from the novel "moon is harsh mistress" It means "there aint no such thing as free lunch" and this really fits my answer. With new technology and competition, the price of things are dropping, but this rule wills still remain true in every aspect.
I will include redundancy into the reliability as well. In general, simpler the system, more reliable it is. but also, component selection can also make a difference.
Design consideration: design like Y6, Octo and x8 also has some redundancy in case of motor/esc/prop failure . So for best reliability, you want tri/quad, but you are trading off possible redundancy of other design. More motor means more weight and more things that can go wrong. Coaxial design also loses some efficiency. So in many ways, you are trading flight time and cost for reliability.
component selection: selecting a good quality motor that is large enough to handle the load is very important. don't try to save money on motors. it is not worth it. ESC wise, I prefer 30amp as minimum with N-fet design. luckily, you can get simonK flashed n-fet esc for good price, but serious guys will run CC phoenix .
Flight Duration vs Wind Stability
I get this question a lot. I need to fly XX min. or I get howling wind all the time. sometime combo. well, good wind performance require higher diskloading and smaller props, which is directly opposed to long duration. you have to decide which is more important and find a balance. In general, you also want to keep the weight low for flight duation. again, I like Y and Quad, but Hexa is ok for flight duration. you want to use low kv pancake motor with largest prop at higher voltage for best efficiency for longest flight, but it will fly really poorly in wind. on the opposite end is small bladed setup in Y configuration (possibly tri) which will give you the st wind stability. tricopter could actually be good compromise, but you get added complexity of yaw mechanism. I tend to dislike hexas because of their poor wind performance. they came into existence due to lack of larger props and motors. but they do have a role in heavy lift situation or if you want long flight. now, is it worth it to make it light? Sure. just make sure the cost is in line with benefit you are getting. for example, Y550 weighs 300gm more than shrimp. when it is released, it will cost about 100bucks more to build, but 10% weight saving is significant. definitely worth it. G-10 to CF. is about 5% frame weight saving at 2-3x cost. so may be 30gm saving for lot of cost. not worth it.
To stabilize or not to Stabilize
Gimbal stabilization has come a long way in very short time. but you do have to make sure if you are willing to pay the cost of having stabilization.
price of stabilization besides money is weight. To start off with, I would avoid all direct drive stabilization. they simply do not work for video. they are ok, for still. for gopro, you may be able to get acceptable result from low end gimbals, but in many ways, i find that non stabilized mounting flown well will give better result. All this mean is that you need to invest in good enough gimbal that gets you the result you want. for some, cheap one may be enough. for others, top of the line setup is needed. (and they can run several thousands of bucks) Look at the videos from users of said product in raw format before making decision. Also, if you want service, be prepared to pay for it.
lot of choices, but for simplicty and easy of use, I still go with DJI Naza. it has usable output, good GPS upgrade and they work well. there are cheaper controllers and most of them work pretty good as well, but most others do require lot of work in tuning. so, you either pay in time or pay in money. all same to me. things like new autocopter 6 are very interesting though.
so recommendation: you can also substitute frame. gimbal and controller to one you like. as well as vendor. these are just an example. this is without camera cost. Gopro2 is about 300 bucks, GF3 is $400 and nex5 is about $ 600
1) just to start, I would consider F450 ARF kit with NAZA and gopro Isolationmount/leg extension combo.
gary can set you up with complete ARF kit or you can get one form uavproducts.com or rc-drones.com total cost is about $520 plus battery/tx/rx great affordable setup with pretty good video. most people I know with higher end system also have this for risky flights. very low investment.
2) you can upgrade to F550 arf for 120 bucks more. you will need F550 LG/Iso adapter for isolation mount so it will cost about 750 total same thing but bigger setup.
3) you can add AG550 stabilized gimbal to the F550. 550+700+=1250 notice the stable horizon. or other good quality gimbal.
you can add Y conversion for $50.00
4) next step up is adding gimbal controller. typically another 200-400 bucks.
and it goes up from here. basically buys you better control. Having decent stabilization does give you more options. worth it for videos.