I've been working on a new helicopter platform the last few months. Based on an MSH Protos heli which I chose because it's an extremely light weight platform, weighing in at only ~1200g without battery. It has a full belt drive which I much prefer to gears as it's quieter, lower vibration and more reliable. I've had a few problems with it because the belt drive makes a really awesome Van deGraaf generator... not a good thing on a UAV. But I solved that, and am conducting test flights now.
The flight controller is a modified PX4v1. I replaced the switching regulator with a MIC29300, so that I can run it on 2S direct with the servos. Main motor power is 4S 5000, typically this heli would run on 6S 3300. Using the MSH stretch kit and 465mm Spinblade Asymmetric blades. In otherwise standard form, this heli flew for 17 minutes on an old crusty battery, in -10C temperatures.
I have now added a subframe to hold an extra battery, FPV gear with a camera in the nose, and a vibration damped NADIR camera mount to be used for aerial mapping. The idea is to develop a mapping UAV that is superior to a multirotor, offering a valid alternative to a fixed wing for short to medium range missions. The VTOL capabilities would eliminate all the nastiness of catapults, and controlled-crash landings with onboard cameras in rugged areas. Even the price is attractive at about $400 for the basic kit with motor and ESC (no servos).
Specifications show the advantage of a heli platform. This machine has an AUW including the batteries and camera of only ~3kg. It is 80m long, and about 15cm wide not including the extended legs, and 30cm high. The blades fold for easy transport, without requiring any lose wires or vibration-prone electrical connectors as a folding multirotor does. It actually looks much bigger on the table than it really is. This seems to be very good compared to multirotors I've seen with the same performance. (payload and duration)
Vibrations are always a problem with helis, but manageable with the right design and construction techniques.
Arducopter really makes helis worthwhile. You could buy two entire heli systems including a Tx for the price of a single DJI Ace One non-waypoint controller. Or 7 for the cost of a single Ace One waypoint enabled controller. I strongly prefer the PX4 controller over the APM and Pixhawk, because it offers 32-bit performance in a small package that is easier to mount in a heli frame.
So does it work? I took it up for it's first photo tests yesterday, and it worked beautifully. Better than 80% photos are usable. It flies for 20 minutes in a hover with old, cold batteries (-5C). I'm hoping for closer to 30 minutes while actually moving (helis are more efficient moving than hovering), in warmer weather with new batteries. It should have an easy cruising speed of 15 m/s with little or no reduction in flight time. At 20 minutes, this would offer an 18km range, and 27 if it can do 30 minutes. If you wanted to do FPV and not mapping, you could configure it with a 3rd battery in place of the SX260 and fly for... 30-45 minutes, and a range of up to 36km. Top airspeed is still TBD, but probably 20-25 m/s.
Wind penetration and stability is excellent compared to both multirotors and fixed-wing. You could do a mapping mission in winds up to 40 km/h with little effect on stability or duration.
If the success continues, I'm going to consider building a large gasser heli. This would allow flight times up to 2 hours, or payloads on the order of 10 lbs for 30 minutes. So you could map large areas, or even perform light duty spraying operations. I'm thinking about local application of a herbicide for things like Giant Hogweed elimination, that sort of thing. Such a large heli does pose significant danger and should only be used in industrial, agricultural or remote areas.
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My electric 700 was shockingly quiet. Quieter than a multirotor.
Gas 2-strokes smoke is not so bad. Much less than a nitro for sure. Of course it makes lots of noise though. I do wish there was a 4-stroke option, as the noise would be less annoying.
I've been flying trad helis since 2005, when the T-Rex 450 was the biggest thing Align made. When the 500 came along I started hanging cameras from one. As noted here in this thread, fine for stills, not so great for video. Next came a T-Rex 600 (which I still fly), with 1st gen Helicommand. Same story, no matter what I tried or how carefully I balanced, video was never great. Thus my helis are now back to being unencumbered by cameras and my AP is all via multis (mainly my notorious APM-addled soon-to-be Pixhawked Flamewheel Hex, "The Witch"). Zero jitter, jello or any other basic problem with the video and much easier to live with mechanically and when flying in close quarters.
Anyway, I've been around both multis and helis for a while. The very last thing I ever want to see is someone who cannot competently pilot a large (say 500+ class) heli launching and flying one autonomously or semi-autonomously anywhere near (by which I mean within a few hundred yards) of any people. IMHO that is dangerous to the point of being criminal, something which will very quickly be recognized by lawmakers and lawyers when the inevitable happens. "Real" r/c helicopters have always been largely self-regulating because they are so difficult to fly. Anyone who has spent much time around a LHS is familiar with the guy with no experience who insists on buying even a 450 and comes back sheepishly a day later with a wad of mangled parts. Now this same guy can buy a 600 (or perhaps even an 800-class gasser) and go fly it at the tailgate party? That is really frightening. A multicopter falling or flying into a crowd is one thing, certainly bad enough (as we've seen), but a big heli under power will be genuine mayhem. I strongly urge anyone considering going to helis to learn how to fly first! And before you even start on that, go see a big r/c heli in flight at your local flying field. If it doesn't scare you (not necessarily in a bad way) then you shouldn't ever fly one.
Aside from which, the vibration problem is in fact not yet solved, and there is no solid reason to think it will be solved either soon or inexpensively. A lot of people have tried for a lot of years. Consider also the size and noise of a big copter; at lower altitudes a big electric heli, let alone a gasser, is a formidable and intimidating spectacle (which is of course fun at times, but a PIA at others).
Regarding gassers, the unfortunate reality is that wet-sump four-strokes aren't available so no matter what there will be some clouds of smoke and mess to live with. The moving parts count rises dramatically with fuel burners, as does vibration, stink and noise.
Don't get me wrong, I love trad helis and if I could only own one single r/c aircraft it would be my T-Rex 600. But I think there are very good reasons, from a whole lot of perspectives, why multicopters have become the aircraft of choice for short to medium range VTOL work such as AP.
I'm quite sure this isn't the final configuration of the landing gear. It pretty much restricts you to taking off from a hard surface. On my 600, sometimes a setup like this will even punch through into the dirt and get stuck. I was actually intending to use the skids here, but I couldn't get them to clear the camera.
Heck, even the entire subframe could get redesigned. I think it would be better to have the batteries to the back, and the camera to the front, with a simple servo driven gimbal (for aiming, not stabilization). That would allow the camera to be used for forward facing pictures.
This design has the advantage however, that since the camera is directly under the CG, you can fly with or without the camera. Or a different payload altogether, even a 3rd battery if I wanted.
Always design compromises. If the basic concept of using a 500 size heli works out, I probably will make a subframe for forward facing cameras. Ultimately, I'd prefer to 3D print an entire subframe structure.
How has the Thunder Tiger machine been so far? I have a good perception of the company. My very favorite RC airplane is a TT Super Decathlon ARF. Purpose designed for their also excellent 46 Pro engine. Designed as a package, it's a fantastic aircraft. The quality of the kit was just incredible.
I was disappointed with the MSH kit, given that it's supposed to be a "premium" kit. Lots of parts didn't quite fit right. The ball links in the blade grips use a machine thread into plastic, which is entirely too easy to strip out. The machined parts had no been cleaned and had swarf in all the holes, etc.
I'm basically to the point now where I would like to start designing purpose-built UAV helis.
Rob: It is indeed a very nice machine and a very easy build, will be running on 8s, 440kv. The giant main shaft, servo linkages(no need for expensive high power servos) and the non-DFC style head(much smaller diameter linkages can be used, less drag) were the main reason I went for it- a 15% discount helped.
I also looked very seriously at the Compass 7HV.
The 880 Sab blades came from Fastlad(UK) but I'm sure I saw on Sab's site that they made to order any size asym from 800-880mm. I'll probably be taking a mould though. I'll do the initial flights with NHP800mm symmetric blades.
The u/c and wheels issue, it was primiarily the autorotation scenario I was thinking of; wheels, skis or circular type 'pan' would provide more forgiving contact/skid points. Good to hear that resonance isn't any more of an issue than normal.
Sean: would love some more details on your setup. That sounds very impressive. Can you tell us AUW, and how many Watt-Hours of battery you are using to go 45 minutes? Any payload at all?
Nick: I looked at the TT820. Nice looking machine for the most part, I like the giant main shaft. But I don't like that it still uses servo linkages. I prefer direct to swash. The linkages seem like needless complexity to me. I really try to reduce complexity in my helis.
I have not had any issues at all with the landing gear. There can be a bad ground resonance when spooling up and down, but I had that even with the skids on this heli. I'm not sure if it's just the blade tightness or what. As far as digging in, what do you mean exactly? It would dig in if you did an auto landing with forward speed. But I'm not doing that. I have actually thought about putting wheels on it.
For sure there's no issue with the control system. The Leaky-I term is a thing of beauty. Prevents any funny business on the ground, but still flies well. And then switching over to full I term in dynamic flight makes it that much better. With 3.1, it actually switches based on GPS speed. Whenever you're not moving, it goes back to leaky I term.
Where do you see 880 Asymmetric blades? Looking on their site, I see 840, then jumps to 910.
One interesting thing, is I see they have CCW Asymmetric blades, never noticed that before. I've really been wanting to build a tandem heli, but the unavailability of CCW Asym blades kill the idea. So I've held off. I see now they have CCW blades, but only in larger sizes, and more importantly, not in matched sets. The CC blades tend to be "scale" blades, with no matching CW blades.
Thomas: The APM for copters does not really allow you to go full-manual if the APM fails. It is something I would like to do, but I'm not sure the hardware is really there anymore. We used to have a hardware Mux on APM1.
I build T-rex 600 and 450 and fly them with sport and basic 3D... They can be tuned very well i think, my 450 are 3 years old without maintanance, only pre flight checks for screw losse etc... My 600 have Bestx FBL system... it can hover by itself ;) even with the wind... I also think about put to her an APM as it can lift 2 KG without problem, is stable in flight like quadcopters... Mechanicaly is not so complicated and if not used for Hard 3D or any it will fly long time once adjusted... Also i like the think if something go wrong with APM i can switch to manual mode and fly like normal heli, when quad goes in oscillation in stabilize mode what then? Acro only? Helis are more safe i think (if You know how to fly them :D)
Nice work! I see a lot of cool things you did and fabricated building it. I like the landing gear too.. Looking forward to more pics, and some videos from your FPV cam :)
Efficiency still goes up with rotor diameter. Propellers have a higher figure of merit than rotor blades.
If I were going to build a camera platform for a DSLR or anything, it would be a heli, for sure.
Rob, very impressive setup- I'm looking at doing similar but with a Thunder Tiger 820(eventually stretched to 880 SAB asymmetric blades). Currently setting up a 450 with Pixhawk.
I'm curious to know if you've had any tip-up issues with the forward u/c digging in on touch down? or for that matter harmonics issues with the tri layout?
Sean, I'm impressed. Which system are you using APM2.5, or Pixhawk?
Hi there!!
I like your idea with using a gas heli. I have attempted that about 15 years ago with my xcell graphite. I bought it for the purpose of aerial video and photography as well as FPV.....lol, I don't remember calling it that though.
Pictures turned out ok but the video was not so good. The 23cc Zenoah was just too much vibration. I actually still have the chopper, never been crashed either. I should get it flying again.......I remember how stable it was, beautiful to fly. With what is available now, this would make an excellent platform. I was thinking of an electric conversion for it as well, but gas is definitely where its at for endurance. May give it a go. Cheers, Steve
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