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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  • Austin, That's an OK unit, but it's got a plastic all over the head. It is also set up for trick flying, thus the 6S battery. I use 4S and have plenty of power, even enough to do tick-tocks, which that Blade is designed to do, boing-boing in the sky. I say so what to that, because it was never my intention to do stunts, only fly cameras.

    Tail rotors are power vampires, loud, and another point of failure, but gotta have it. This is why I tried a very large coaxial with collective pitch. Too bad it's too difficult to engineer that in a small size, it worked, it was amazing, but it was so complicated it almost needed the head to tune itself in flight. And really expensive $1000 for the frame and mechanic.

    The Blade series is good, I had a 400, all metal. Rob suggestions are great, but pricey. I would try and find a bare bones kit, concentrating on the quality of the head, then you can get your own power system, different pinions, and that would allow you to try different head speeds. Believe me RTF=RTC! You have to go over it, so you might as build it. Don't forget the locktite, they did! The HC-500 is made by Sonix and is a great machine.

    Check out cnchelicopter. They have upgrades for everything at a higher quality than Align, and the HC-500s come from the same guys, I'm pretty sure, only Heli-Direct and them have it. 

    Another thing you might want to try is going over to RC group's classifieds, and buy cheap,everything from someone who is bailing out; their uncrashed heli, that they're scared to fly, and all the parts from when they did crash.

    Rob, nice physics lesson. Check this: The Heli-Baby coaxial has a rigid head. What happens if you put fiberglass or carbon blades on it, (notice they are plastic), self and complete destruction. The blade themselves are the dampeners. Go figure.


  • Oh, and this teetering hinge vibration effect... also occurs to the tail rotor.  And in fact, it's probably much worse, since the tail rotors typically have absolutely no ability to flap at all!  I believe this is the source of the higher frequency, quite loud, buzzing sound that I've noticed from the heli in fast forward flight.

    The advancing blade will produce much more lift than the retreating blade, and the the tail rotor blades cannot flap to equilibrium at all.  Therefore they will produce a very high vibration indeed. The only saving grace is that it tends to be at 4X the RPM of the main rotor.  

    The main head can flap to equilibrium, it just transmits some force through the dampers while it's doing it.  

  • Roughly speaking, if you had a 4 blade set with 35mm, vs a 2 blade set with 69mm, then your "disk solidity ratio" will be roughly the same.  If you use the 69mm blades on a 4 blade head, then your solidity ratio will be almost double that of the 2 blade head.

    Solidity ratio is pretty much ignored in RC helis, but it plays some significant roles in full-scale.  One of the clearest effects, is that a high solidity ratio allows you put put more power into the air for a given disk area and RRPM, before you end up with blade stall.  So again, for a compact heavy lifter, you would want multi-blades, with a high solidity ratio.

    Now, the choice between low RRPM and high solidity ratio, vs. high rpm and low solidity ratio... get complicated and gets into a lot of issues related to structures and handling of the aircraft which don't really apply on our scale.

  • I'm not sure what caused the mushrooming. Last rebuild I did the feathering shaft also. I'll see if it happened again when I try the red dampers.


    David Boulanger
  • What causes the mushrooming?  I wonder... if the sleeve could be deformed, and shift over such that the "pivot" were not centred, that would probably cause a really bad vibration!

  • Rob. I have looked at the Spinblade sets. I'm not a aerospace engineer but the cord length is shorter because you have more blades I guess. Sooo, how do you figure out if you get more lift, more drag, or what the headspeed difference should be compared to a 2 blade set. Trail and error like everything else I guess. It's just a big chunk of change to experiment with it.


    David Boulanger
  • Just doing some research into the concept of changing to a multi-blade head.  One issue to consider it blade availability.  Spinblades do offer Asymmetric sets for multiblade heads.  But upon closer inspection, I notice they are actually much narrower than the 2-blade sets.  35mm vs. 69mm!  I wonder if you could go with a 4 blade head, and run 2, 2 blade sets, with each pair arranged in opposition to eachother to maintain balance.

  • I use the plastic sleeve and have had to replace it about every 5 hours of flight time when I give the 550 a go over. The ends of it mushroom out a bit. I'll try the red ones and see if the video improves with lower headspeeds. Just so everybody understand's, this is not a vibration problem with the APM. The logs look about the same at 1500 or 1900. I'm just trying to take clear 1080 video at 60fps with the lowest headspeed I can without having to hang some big contraption off my 550 frame to handle vibrations.


    David Boulanger
  • Austin, well, you could look at one of these MSH Protos.  It is a 500 size, and is surprisingly reasonably priced.  It's not perfect, but pretty good.

    The Gaui X3 is also a nice machine.

    And of course you could consider the T-rex.  The Tarot clones are typically very good quality.  I have found some Tarot parts to be better than genuine Align.


  • @Thomas - Thank you! If I was to buy one today, and I will, what would you recommend as an entry copter in the 500-550 range? I want to stay really low priced. I don't need something incredibly powerful and 3D, just something to fly with. I might not even set it up to do 3D, just have a positive pitch curve on p1, maybe a 3d setup on p2. Do you think this would suit my needs? I found it for around $300 from a few vendors. What do you think? Thanks!

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