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.
Comments
It seems to me even professional helicopter engineers don't always understand exactly what's going on either.
For sure, if somebody starts talking about gyroscopic precession, they don't really know much about the subject.
Yes a true dynamic balance is not only possible on a helicopter, it is solved for routinely. The difference for RC is the rigidity of the blades really make them respond more like propeller blades in a horizontal plane. Most balance on a helicopter is solved with two or more accelerometers in lateral and vertical planes. Adjustments are weight, angular displacement, pitch change rod and trim tab. Some adjust for chord imbalance. You are right about one thing though, the aerodynamics of the helicopter blade are very complex.
If the rotor is truly balanced, the video will be fine whether the rotor RPM is synched up or not. Remember though, there is a vertical component to the "balance" of the rotor as well and the effect increases with airspeed.
The "wake" effect is overstated. The blades talk more across the disc through the hub, than through a loose aerodynamic couple.
I thought exactly the same thing when I realized everything that was going on. I guess they just have to be careful not to do any low-G manoevers.
Yep, I end up there a lot. It's a bit head-explody at times but really good. Sometimes the pages for certain topics seem more like he's asking questions rather than providing answers but... it's thought provoking in any case.
Yes, understood. Neither is a basic balancer going to achieve dynamic balance. I use the both in combination. Exactly the same weight, and balanced on a balancer. I believe that does give a good dynamic balance?
My understanding is that it is more closely related to the solidity ratio, rather than purely the number of blades. So you could achieve the same power with less, but wider, blades. The reason this typically is not done, is mostly structural. Wider blades have much higher chord-wise moments of inertia. This results in higher forces needed to actuate the cyclic pitch, compared to achieving the same SR with more, narrower blades.
Another reason to choose more blades over wider blades is as we are discussing here, lower amplitude higher frequency vibration, and higher cyclic response rates.
Yeah, I wonder about this too. There's the idea that with more blades, each blade is travelling closer to the wake of the blade in front of it. But this ignores the idea that there is a whole column of air moving down, so the blades aren't really running in a wake. This sort of thing is much too complex to solve with some hand waving on an internet forum. ;) Really needs testing.
Digital video is usually 30 fps, or 60 fps. Analog is 50hz with PAL, 60hz with NTSC.
I've heard that lining up the rotor speed with the frame rate will solve the vibration, but I don't know. I'm trying to get the system such that you don't have to worry about that.
David, I think just about any Canon P&S running CHDK will make a better AP camera than either the GoPro or Olympus. I've got the SX260 on my heli. There's a smaller one though some are using, an Elph, not sure which. It's not much bigger than than a GoPro, better photos, and you can get an intervalometer with CHDK.
Regards
David Boulanger
David, I have a TG600 I use as a beach or adventure camera. It's... ok for what it is, but it's very good. The quality of the picture is about equivalent to a $100 P&S camera of the same vintage. The cameras are basically cheap P&S's in an expensive tough body. So like I say, good for a day at the beach or other places you don't want to take a good camera, but not really the best choice for any serious efforts.
Just thought I would post a picture of sunny south Florida while most of you are cold. Rob's snow covered houses are
pretty also.
Jim,
This is all about video for me. 60hz would be correct. 30 just doesn't seem workable at all. As the rotor speed increases the video changes characteristics. Low rotor speed of 1500 the video is shaking. speed of 1700 (higher frequency and lower amplitude) the video has mild jello to it. 1900 - 2000 ( even higher frequency and lower amplitude) the camera no longer sees the vibration. I have so far been able to carry whatever battery weight with out problems. I use 5,8,or 10 amp capacity when flying. I have yet to try 16 amps but don't see a problem with it but I would have to move equipment on the airframe around to have proper balance. As this topic has evolved I am starting to lean towards a four blade head with a set of spinblades designed for such a purpose ( shorter chord ). If I was just taking still pictures two blades would be fine. I am still going to try a few more camera mount options to see if I can dampen the vibration better. Firm mounts have proven to work better. Hope to fly tomorrow morning.
Side note here. Olympus just released a new camera that may be usefull to this community. The TG 850. 1080 video at 60 frames,16 MP, 7.5 oz., and it has the ability to take pictures at a preset time interval. Its bigger than a Gopro but 16MP and a variable zoom lens at $250 sound attractive.
Regards
David Boulanger
This has a bit to do with video - the video is directly impacted by the inherent vibration in the platform compared to the frame refresh rate on the video. Anyone know what the frame rate is on the various video cameras? Im thinking it is around 60 or 72Hz. Am I totally off on this?
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