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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  • Is everyone making their own cables for the gps/mags. I was thinking of using a sheilded cat 5 cable. Thought anyone?
  • What is the recommended firmware for traditional helis at this time?
  • Understood.... My partner in crime and I just got the new Trex 700e HV Pro DFC. It seems pretty solid of design but i get what your saying and we will consider it while we build and design. Since we already got the air frame we will have to live with it for now. If we see issues we will look at swapping the head. Going by my calculations we should be getting a head speed of 1200-1300 RPM. That should be a relatively mild speed for this set up with no payload for now. What are your thoughts?

    Thanks for the help... I appreciate it. 

  • Oops, I must have been typing my comment as Rob was typing his

  • Joseph,

    If Rob doesn't reply, I'll give you my guess as to why Rob doesn't like DFC heads.

    Basically because the DFC head is a "rigid" rotor head. Meaning the blade grips are not able to teeter in the head block whereas all other R/C rotor heads are able to. Ever notice the rubber o-rings in the main head block that you push the feathering shaft through? Those are there to allow the feather shaft to teeter and absorb external forces that a rotor head may experience in flight. The DFC head still contains these o-rings (very very hard rubber - but still there nonetheless), therefore when the main head does teeter even just a little bit, there's a TON of stress going on in the DFC linkage at the blade grip end since they can only work 90 degrees to motion rather than a typical ball-link. I hope what I'm saying makes sense...Hopefully Rob can fill in on the points that I missed.

    As far as a 700 sized AP ship headspeed, I've done anywhere from 1200 to 1400 rpm.

  • Hard to say on the speed, I haven't got it nailed down yet.  I've seen people fly them at 900 rpm, but that's with no payload.  1400-1800 is probably a good range, but you do have to worry about vibration.  The lower the head speed, the worse the vibration is to deal with.

    DFC heads are a poor design.  The linkage is overconstrained, and tend to place the pitch control links under a cyclic bending load.  Cyclic loads are bad. There were failures early on, though I think they've beefed up the design so the acrobatic fliers can live with it... how reliable though in a UAV application?  Also, the DFC relies on very very rigid dampers to solve this problem.  Rigid dampers are bad for vibration.

  • Rob, 

    Also, what is the ideal head speed for a 700 class camera none 3d aircraft

  • Rob, 

    What don't you like about the DFC heads?



  • What would be a good safe starting point on a stock Align 700E ? A friend and I are now venturing into traditional helis now that we have been building and tuning Multi-copters and planes for 3 years.

    Rob, with all your great success with this style ArduCopter, Could we PM you while we progress thru the build and tuning?

    Thanks for the support and knowledge.


  • Yeah, I never tried it, and don't recommend it.  I'm 99% sure you won't get a good result, and it may crash your heli.

    Autotune does not look at the Rate FF, which is really needed for good control.  And the lowest Rate P number it will use is too high for some helis.  The heli could tear itself apart.

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