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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The response to input is much faster and positive with a heli. due to the higher air velocity towards the blade tips. If you take a multi rotor it can stabilize to about 1.5 degrees on a calm day and anything up to 5 degrees on a very windy day. Other factors are also involved but basically is has more compressibility in the response which equates to less resolution. That is the reason why small dia props (higher velocity) produce better stabilization that larger ones.
That same IMU can stabilize a brushless gimbal to about .5 degrees and with a VCA .005 degrees. What makes the MR so bad is the low airspeed. The Heli is much better but I cant say that I have had the need to measure it yet.
Terrain following, i2c sonar on pixhawk(is it available yet?), rounding corners, dual voltage measurement, above mentioned gasser applications. The list goes on and on.
Interesting. I would like to build a gas engined helicopter, but I'd be concered about the autopilots ability to cope with engine failure. Correct me if I'm wrong, but I think that the current software would stall the rotors and the heli would crash with an engine failure. It would be useful to have some kind of autorotation routine to cope with such an eventuality. I would also hope to see an engine interface module to for interfacing with sensors for temp, rpm, etc. That way, an operator could monitor its condition.
Helis rock! I can attest to that. ;)
Yeah, I just know the larger heli I'm training up to will not have flight characteristics even close to that. Low speed, heavy lifting, large blade, long endurance gaser, which makes it nice and stable. I just don't want something with rocket characteristics to learn to fly on ;) I guess I can just start with much reduced rates and fly from there ;)
The tail can not produce enough power to keep up with a main in FFF.
OK, gear ratios, and motor kv. The lower the kv, (volts/rpm 830kv with 2 volts=1660 etc.), the lower the rpm. That's your pinion rpm. (just in case you don't know what that is). So # of teeth in main/# of teeth in pinion x kv = your headspeed.
That said, I fly with a governer. Some escs have them, Scorpions do. I spin up to 2200 and the throttle stick only controls blade pitch, (flight mode 2). Flight mode one is normal. You can select an exact headspeed with your tx's throttle curve, you flatten the curve in mode 2, at the desired level.
So get a higher tooth count pinion, slow the speed. And the reverse, more teeth in the main, etc.
That Blade spins fast, higher voltage batt, higher top end rpm. That's so you don't "bog down" the head when stick whacking, (tricks). 2000-2200 is fast too. Why?, very little pitch is needed to make it go. The results are a very smooth and accurate flying machine, with a huge momentum driven reserve of power there if you need it, and you probably will.
I've always wondered why forwards is forwards in a conventional helicopter. If forwards were sideways then your tailrotor flapping problem would (largely) disappear and the tailrotor thrust could be made useful rather than parasitic.
#1 easiest way to reduce the headspeed is to reduce the voltage. My MSH is designed for 6S, and I'm flying on 4S, and with a small pinion. There's absolutely no need for HV on something like this. I'm only drawing about 20A total.
Thank you! How should I set up the powertrain to get a slower headspeed on larger blades? I don't need an advanced 3D flyer, I need something that will just fly around well. Thanks again :)
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