gtranquilla
RadioActive
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End in sight for current MR designs!
- Thread starter gtranquilla
- Start date
gtranquilla
RadioActive
In some respects it seems simple especially for the 9dof IMUs. With respect to the mechanical design it might be a long way to go........if the upper rotor is powered separate from the lower rotor, two speed controllers would enable yaw control ....But roll control might still be required which means that swash plates are needed (probably on both rotors).....and then there are four blades to control for each 4 rotor fan...... sounds like a big $$$$ R&D project.....
Matt Sharp
Member
It's really no different than a cp heli. The coax design would just add unnecessary complexity, and the pusher fan on the back is pointless on an rc aircraft. How fast do you want to be able to fly?
gtranquilla
RadioActive
From what I understand so far.... the Quad, Hex and Octocopters have more stability that do the large rotor helicopters.... in the sense that you can park them at a 3D spot in the air and focus your attention on other things such as camera gimbal control.... (although the hover can sometimes drift up and down at least the 2D GPS position remains solid)....... And from what I understand from the above video.... the Sikorsky X2 has superior stability and handling over the conventional CP chopper........ A Video producer indicated to me that my 800mm Hex seemed a bit slow for forward flight for his plans.... although I did not fly it in manual.....so the Sikorsky X2 pusher prop does the job without the main rotors moving off the horizontal plane.... .
matwelli
Member
the point of quad/hex/octo/whatever multirotors is the fact they are based on simple motors and propellors , survive the odd impact and cheap to repair combined to a heli
the above example is not
there are a couple of quads that have had a pusher fan attached ( i played with a prototype early this year) so that part is do-able
i
the above example is not
there are a couple of quads that have had a pusher fan attached ( i played with a prototype early this year) so that part is do-able
i
Matt Sharp
Member
A coax by design is more stable than a typical cp helicopter, but when you add a controller similar to what multi rotors have they become as easy to fly as multis.
I agree with matwelli though, that the simplicity of multirotor design makes them great. That's the main reason I fly cp's for fun, but fly a multi for camera work.
maxwelltub
Member
If I had the time and money I would only fly CP helis, the simplicity of MR's is what draws me to them. A coax-ax with a pusher prop doesn't hold any advantage for UAV AP that I can tell.
gtranquilla
RadioActive
I am thinking that conventional helis can sometimes be landed safely without power by means of counter-rotation with rotor pitch negative until close to the ground.... then positive pitching the rotors just before landing...... Can't do that with a quad, Hex or Octo.... and for AV work... getting an expensive camera down safely would be a high priority........ (ofcourse the RC control system power would be separate but very low current draw).
Carapau
Tek care, lambs ont road, MRF Moderator
Hmm I reckon that a well setup 700+ class CP heli is every bit as stable as a MR and is a better airframe all round. Most people dont bother with them though because a/ they are harder to fly and b/ they are harder to set up correctly.......discuss
gtranquilla
RadioActive
Please confirm..... are you able to safely land your 700+ CP heli with rotors free spinning, i.e., no power to the rotors?
Matt Sharp
Member
CP heli's can autorotate. 450 Size are the smallest I've tried and it is quite a handful on that small of one. 600 size and up auto very well. Ap ships are a different story because of the added disc loading and slower head speed , but they can still do autos.
gtranquilla
RadioActive
In any case I am a firm believer that coax can be as efficient as single props when done correctly and possibly more efficient as was indicated by Howard Hughes aeronautical engineers back in the 40's....... and this new Sikorsky X2 claims the same....
Matt Sharp
Member
I don't see an application for it in RC though. The biggest issue would be complexity in rotor head design. You would need dual swash plates and complicated mechanics to control the mechanical interactions.
matwelli
Member
first off - great discussion so far its great to be able to throw this sort of stuff around
what i wonder about , is can a co-axial autorotate ? i would think the lower disc would block the upper
@Dewster - you mean a bicopter ? theres a few around, have built a few myself - great fun
its great to be able to throw this sort of stuff aroundwhat i wonder about , is can a co-axial autorotate ? i would think the lower disc would block the upper
@Dewster - you mean a bicopter ? theres a few around, have built a few myself - great fun
Ghostrider
Member
There are already plenty of examples of co-axial r/c helicopters. For example, the blade series of helicopters for beginners are co-axial. They are of course fixed pitch. I have seen videos of collective pitch co-axials though. There is no reason why a co-axial helicopter would not be able to autorotate, but the smaller rotor disk would likely mean less stored energy on decent and less margin of error to land safely.
When it comes to stability, a conventional helicopter definitely has more than a multirotor. The gyroscopic effect of the main rotor blade and the cyclic controls give them stability and control authority that multirotors don't have. Multirotors do come across as being easier because of the common use of GPS and self leveling flight controllers.
When it comes to stability, a conventional helicopter definitely has more than a multirotor. The gyroscopic effect of the main rotor blade and the cyclic controls give them stability and control authority that multirotors don't have. Multirotors do come across as being easier because of the common use of GPS and self leveling flight controllers.
DucktileMedia
Drone Enthusiast
Ive thought about this design a few times and think its great. There is a guy that has a turbine powered coaxial with dual CP heads. it's nothing short of awesome but it is complex and very expensive. the big reasons to look at these are wind, inherent stability, high payloads for their size, auto rotation, and possibly efficiency. but I agree for now that multis are the way to go.
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R_Lefebvre
Arducopter Developer
This is all a bunch of speculation that is pretty much completely untrue. I have seen it many times before. Most people who think that multi-rotors are inherently more stable than helicopters, only believe so because they have never flown an electronically stabilized helicopter. And I don't mean a flybarless controller, but a proper stabilization system.
I'm in the some what unique position of having flown several multi-rotors, as well as helicopters, on exactly the same stabilization system: Arducopter. It's the only way to get a good apples-apples comparison. In this case, it's pretty clear. Helicopters are inherently far, far more stable than multi-rotors. There's just not even any point in discussing it. They're less affected by wind, and the controls are more responsive.
As to coaxial helis, I don't think they provide any extra stability over a conventional helicopter. The only reason why we associate coaxial helis with stability, is because the beginner coax's were designed that way. There is virtually no way to make a single rotor heli as stable as a coax using mechanical means (ie: the weighted flybar on the top rotor of the Coax). But it's very possible to do so electronically, and that's just what we've done. A 450 heli, which is normally a squirely beast, is very easy to fly with Arducopter. It's as easy to fly as a Blade Coax heli... unless there's wind, in which case it's far easier to fly than the coax which becomes uncontrollable with only a little wind. A 600-700 heli with Arducopter is just a *rock* in the air.
As for the pusher prop, exactly how fast do you want to go? I've had my 450 heli up to 120 km/h, straight line, no tail wind. My 600 I've had up to 140 km/h, and the speed was still climbing rapidly but I run out of room and have to turn around. A 600 class heli is capable of over 200 km/h.
Yes, exactly. The only point to a multirotor, is that it's dead-nuts simple. Has 4-8 moving parts. And you can crash it upside down and maybe only have to replace a few props. A helicopter has 100 moving parts, and even a very mild crash can cause $100's of dollars in damage, and require many hours to repair properly.
They are not harder to fly, when using a good controller. They are much more difficult to set up mechanically, and also somewhat harder to tune the controller... though I'm making progress on that.
Another couple reasons why helis are less popular:
1) There are simply less controllers available. The multi-rotor market is flooded with stabilizing controllers. Helicopters have very few. There's obviously Arducopter. DJI has the Ace One, Wookong-H and Naza-H. And just recently many of the FBL controller manufacturers have come up with add-on stabilization and GPS position hold. But if you want waypoints and RTH, you're left with only 2 options. Arducopter, and Ace One, with the latter costing $11,000.... meanwhile a Naza-M will do RTH and costs... $400?
2) Heli users historically have machismo about their operation. They have up until now, shunned stabilization, as being only for sissies. Meanwhile, multi-rotors do not have this affectation, because they are simply unflyable without stabilization anyway. So stabilization is accepted for MR's. This in turn, drives the market to produce many competing systems which keeps the price down. Helicopter market has less competition, and thus higher prices. But even worse than that, the Heli market is hugely affected by the idea that "you get what you pay for". Most will simply not even consider Arducopter, because it's just far too cheap. I'm quite sure, that if I took a standard APM 2.5, changed the colour of the board, claimed it was a special heli edition, put it in a nice machined aluminum case, and charged $1000 for it, I'd sell tons of them.