New build - long distance?

Hardware Multirotors
1

Hi all,

I’ve been playing around with a simple F450 frame and some motors from unmannedtech (shop in the UK). I got an old APM 2.8 from them as well and i’ve gotten this up and running to do some autonomous flights. I don’t have a camera on it (yet). I don’t have telemetry on it. It just flies where I tell it to go on a map.
The aim of this was to learn, and i’ve learned a lot. About Esc’s. About fibration. About ArduCopter and how great this (open source) software is :slight_smile:
I’ve also learned that the APM 2.8 is old (i knew this when buying) and why this is considered an old platform.

The aim of this is to create a drone that can do a visual check somewhere on a farm. Check some lifestock in a field, check a water hole, etc. Stuff that you would have to drive out to a point, get out of the car, have a look and get back. Because of the farm roads, going as the “crow flies” would be a lot quicker and hopefully saves a bit of fuel.

So, now i need to figure out what frame i should use for the real thing. The main question - probably - is the distance it needs to cover. At the moment i’m looking for 10km distance one way. So that would be 20km distance.
The current F450 frame with S3/2200mah battery flies around 12minutes. I know this is likely not enough for 20km :wink:
Some people probably would suggest a VTOL, but i would like to keep it a quad or hex, because i think that is (at the moment) a lot better supported.

So, i’m looking for advice on frame time, motor/prop config and battery size!
I’m not afraid of abit of DIY, so if you suggest to just get 4 arms, a few carbon plates and that is - that’s also ok. If you feel i should study some more documentation around how thrust/motor/prop stuff works and how i can calculate the flight time, than that would be even better.
I know flight time is very dependend on a lot of things. Frame weight being key of course, but also wind. So I know any calculation will just be theoretical.

1 Like
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Multirotors are the worst efficiency case for flight time and distance. The faster they try to go, or fly in wind, the more power it takes. They are best for hovering type work, or short distances.

I would consider a fixed-wing airplane. Or if you want an aircraft that takes off and lands vertically, can go fast, is pretty much impervious to normal wind conditions, and gets more efficient in cruise than in hover, consider a helicopter. I fly way more than those distances all the time with heli’s. For a gas engine helicopter flying at 50 mph that flight would only take 15 minutes.

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Hi ChrisOlson,

Thanks for the response. I do have a simple Trex 450 as well, but haven’t dared putting the APM on it.
How would you say i should get started on something like that?
I do have expirience with RC cars as well, so the petrol doesn’t really scare me. What heli’s do you fly with? How’s it building one of these things with a pixhawk? My drone can crash and maybe a prop is lost, but a heli - different story :slight_smile:

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The 450 is about the minimum size you can put a APM or Pixhawk on, and probably wouldn’t be a be a suitable platform for your desired job for the drone because of its performance limitations.

I fly 500, 600, 700 and 900 size with Pixhawk. 500 and 600 electrics, 700 and 900 piston engines. For the big piston heli’s this flight would barely get the engine warmed up. They fly for well over an hour at 80 km/hr cruise speed. My 600 electric could also do this flight carrying all three batteries on it at a cruise speed of 60 km/hr. It will fly for 28 minutes at that speed carrying 15,000 mAh 6S batteries.

Admittedly, setting up a helicopter is not as easy as a multi. But it is not exceedingly hard either. The advantages of the heli compared to a multi is that it has much higher payload capacity for the same power (making carrying more batteries or fuel possible). It can go much faster on the same power (making long distance flights possible), can be powered by either electric or combustion engine, is able to autorotate and land safely will loss of power in flight, and is less affected by wind (able to maintain ground speed with headwinds that will kill the battery in a multi).

Crashing either one at these flight speeds will result in significant damage to the aircraft. That is a non-issue.

Since you have a Trex 450 and a APM, I would experiment with it and learn how to set it up. The APM can run AC3.2 which flies a helicopter fine. And once you get more familiar with heli’s, look at building a 600 size electric or 700 size gas to fly your mission. It is trivial to get 30 minutes of flight time from electric helicopters of sufficient size (600 or larger) that can carry a decent payload in batteries.

The other option would be to look at a fixed-wing airplane. It is pretty easy to get a fixed-wing to fly for an hour. And the fixed-wing would likely be much cheaper than a helicopter. But the fixed-wing does not handle wind as well as a heli, and you must have provisions for takeoff and landing - either a runway or hand launch it for takeoff, and either runway or crash belly land it for landing.

The main reason I use helicopters instead of fixed-wing is because of their power and ability to maintain speed in the wind. Helicopters can fly in conditions that will ground a fixed-wing.

In any case, this is far outside the practical limitations of multi-rotor aircraft. They simply are not efficient enough to make it worth considering. A multi-rotor must achieve such a radical frame angle to cruise at any decent speed for long distance, that their power requirement is too high for the weight they carry.

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Hi Chris,

Many thanks for the response. When you mention piston, do you mean nitro or petrol? Petrol would actually be practical. I don’t know any rc brand that does that. Could you suggest something?

I’m worried about trying the 450 with the Apm that I have now. Had one crash with that when I tried to hover it and that was expensive. I don’t like the idea where learning = crashing. I’m open to the idea of a heli, but really need a bit more to get going. Would you mind telling me more about the frames you use?

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Either 15% nitro or gas. Nitro makes a lot of power in a small lightweight package. There is no ignition system to go bad. But is expensive to fly. 15% nitro fuel here is about $30US/gallon.

Gas is normally done by starting with a nitro frame and doing a gas engine conversion on it, like from Helibug using a Zenoah (or similar) two-stroke gas engine. 20-25cc weed whipper engines make excellent gas powerplants for RC helicopters in 600 and 700 size. There are few manufacturers who build turn-key gasser helicopters. Just about all of them build nitro models that can be converted.

Helicopters are harder to learn to fly than multi-rotors. I would suggest taking your Trex 450 to a RC club someplace where there is an experienced pilot who is willing to teach you how to fly it. That is the absolute best way to learn how to set it up, and how to fly it - getting hands-on instruction. The other way is to invest in a simulator and at least get the basics of hovering mastered on the sim. And then move to the real thing.

I have flown mostly modified Align Trex frames, mainly because the parts for them are readily available from just about anywhere, and they are quite economical to build and fly. And they are quite reliable. I also fly a Gaui GX9 with a Stihl chainsaw in it (which has not been as reliable as the Align models). And I am currently building a Velos 880.

I did build a hybrid TriCopter/fixed-wing with a 1 meter wingspan that could do your proposed flight parameters. However it proved to have quite a problem with wind. It’s maximum flight speed is 35 km/hr and it flies for 50 minutes on a single 4S 10A battery. Unlike most multi’s, the power requirement to keep this one airborne goes down in forward flight instead of increasing

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I could do more experimenting with it to try to get it so it’s stable in the wind. But the problem I have at present is that the wingtip motors throttle back so far in forward flight that they do not have adequate thrust capacity to keep it stable in the roll axis. It flies beautifully in no-wind conditions at 35 km/hr. About the max wind it can handle and still fly decent is 10-12 km/hr. I fly it with the stock TriCopter code. It could probably be made more stable by building a better wing, using possibly a tractor (vs pusher) prop for forward flight, and add control surfaces to the wing.

So in multi’s something like this is also a possibility - a hybrid. Tri’s are more efficient than quads. Quads are more efficient than hexes. Hexes are more efficient than octos. Helicopters with a single rotor beat them all. Fixed-wings beat helicopters. But with some experimenting a design like this Tri could have VTOL and approach fixed-wing efficiency. If you are the type that likes to experiment and build things, that is worth looking at.

The VTOL code for fixed wings is basically an airplane with a coaxial quadrotor setup strapped to it to make it VTOL. I have no experience with those and am not interested in them because of the complexity and basically dead weight you are carrying in flight. Others here do have experience with them.

Another possibility in multi’s is so-called “tail sitters”. It is a fixed wing airplane that sits on its tail, takes off using TriCopter setup, tilts ahead in flight to where the wing is making lift and uses the TriCopter motors for propulsion and stabilization. Again, I have no experience with those, but I thought I read where the code supports it - tridge possible wrote code for them.

These are all the possibilities I can think of at present. Of all of them in a VTOL platform, the helicopters will lift the most payload. Can easily fly as fast, or faster, than fixed-wings. Are proven and not experimental. Handle wind the best of any other platform. And are relatively simple considering all they can do. There is likely a very good reason in the real world of full-sized aircraft that you see all those helicopters flying around doing everything from air ambulance service to being used for sky cranes. There has not yet been anything invented by man in a VTOL aircraft that can do what they can do. :grinning:

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In my experience a multirotor use most of the power to stay in the air so flying at 3m/s or 12 m/s have more or less the same consumption guess there is a kind of wing effect when increasing speed.

I have build and sell a quad that with 16" props, 250 grams payload and 8000 mAh 4S batteries flies around 45 - 50 minutes with normal batteries.

If you need more payload or flight time go for a plane , an helicopter is the best solution if you need a big payload because a multirotor will have more and more problems to control propellers as they get larger then 18".

Consider that a multirotor has a good efficiency with 11 grams/Watt , do better is not easy while a plane with 17 grams/Watt is quite normal.

Wind can be a big problem for a multirotor , a lot less for a plane or an heli.

Chris, nice job for your tricopter , a better version of the HobbyKing , “black led”, tricopter .

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You asked about what frames I fly. This is a little video I made of an ArduPilot flown helicopter flying on full autopilot. Doing actual farm work, flying crops for crop insurance imagery. Just so you can see how well ArduPilot can fly a heli. And it is a proven design and size that would work for what you want to do, with no guessing.

This particular helicopter was an experiment this year to see what kind of performance I could get from an electric platform, vs piston engine. And overall, it has turned out to be a quite impressive and very reliable aircraft for doing this type of work with it. It has become my favorite to fly because of its relative simplicity, and ultra-smoothness in flight. As flown in this video, it has a takeoff weight of 5.1kg, has a maximum range of 15 km, and most efficient cruise speed of 45 km/hr. It has a XT60 plug ahead of the motor that I can plug in a third 6S 5000 battery installed in a removable belly rack, and increase its flight time to 28 minutes in cruise with a maximum range of 20km. It could easily carry yet a 4th 6S 5000 battery if I wanted to.

IMO, this is an excellent size for electric power. It has the weight, power, and performance to handle wind up to 30 km/hr. Is much simpler than piston engine helicopters. And it is not expensive (considering its performance capabilities). It would be just a matter of getting over the hurdle of learning to fly it. You could possibly build a multi-rotor that could keep up to this thing. But the cost would be easily double what it cost to build this helicopter for UAV use. The downside, as you noted, is that the heli’s learning curve is a bit steeper.

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I can get a 600 helicopter at 5kg takeoff weight to hover for 40 minutes too by running the headspeed at 900 rpm. Only problem is, it’s not usable for anything. So I gear my helicopters to run at a happy medium between flight time and power to handle wind. The heavier the disc loading, the better they handle wind. And that’s the problem with my TriPlane - it has 16" props and very long flight time - no wind handling ability and no flight speed for decent range, and poor stability.

The 600 electric heli I pointed out is about 14% more power efficient in cruise flight at 10 km/hr higher cruise speed than the TriPlane hybrid is. The sum of the prop tip losses, and other associated losses in multiple drives simply cannot compete with a single large rotor running a blade tip speed of 110-120 m/s, at ~3.9 kg/m^2 loading, for power efficiency.

The problem with most RC helicopters is that they are designed and set up for extreme power 3D aerobatic flight. For UAV use, you do not need the kind of power and collective/cyclic pitch range it takes to make a helicopter stand on its tail and do tic-tocs like it is possessed by some sort of demon. It takes some modifications to the drivetrain to make them suitable for UAV use.

Multi’s are all the rage because they are simple - make a box to hold a battery and some electronics, bolt four sticks to it, hang motors and props on the ends of the sticks, and you have a device that flies. But it is not efficient. And there is no combination of trickery you can use to make them more efficient. They are nothing but proof-of-concept that if you strap enough horsepower to a brick you can make it fly. They must achieve a fairly radical frame angle to go anywhere at any decent speed that provides range. They are very nice and convenient, easy to fly, and safe for all the millions of people that want a platform to get a camera in the air and do aerial photography, which is their primary use. But they are not long-range, high-performance aircraft.

The 600 helicopter can kill you - easily. Get hit by those main rotor blades and you will be missing body parts. Get hit anywhere in the head with it, and you are done - making a trip to the morgue. Helicopters are not safe to fly around people and use them for the flying camera platforms in the areas that a lot of people fly multi-rotors. But in a rotary wing VTOL aircraft, they do provide the practical performance necessary for high-speed, long-range flight.

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I agree that an heli is more efficient than a multirotor, in real world people fly with heli and planes not multirotors.

But as you said multirotors are very simple , for a large majority of air jobs , 30 minutes with 1 kg payload is enough so there is no doubt that multirotors are a big success also considering that cameras will be in the near future more powerful and lighter .

For special conditions, as strong winds or high payload with vertical landing an heli is the right choice , Rob Lefebvre made a great work with helis .

An heli requires an high maintenance and has you wrote a big heli is a big danger, so if vertical landing is not mandatory I thing that a large plane can be a good answer for long range and high payload .

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Airplane by far is the best option for long-range efficient flight. But they do require special provisions for takeoff/landing. And they can be grounded in windy conditions, common in rural areas.

Multi-rotors are not practical beyond RC because there is a limitation to how fast you can accelerate and deccelerate propellers to make them stable. They are by far the most popular of all RC aircraft due to their simplicity, low cost and easy to build. The OP’s intended use, however, is outside the practical use of multi-rotors.

RC helicopters are not high-maintenance unless you crash them all the time. Especially electric ones. Gas helicopters are more maintenance due to vibration and regular engine overhauls. I do not recommend a piston engine helicoper for somebody new to heli’s. However, the OP mentioned he has a Trex 450. Perfect platform to learn and experiment with, as the job he wants to do is easily within the performance envelope of a larger heli of 600 class or bigger. And being he is making flights to check cattle, I would assume a rural setting where the danger issue would be moot. Ranchers use full-sized manned helicopters for the same purpose. Ranching happens to be the third largest market on earth for light utility helicopters

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Hi guys,

Thanks for all the replies. i have a lot of research to do :slight_smile:

it’s very impressive to see that the heli just operates. Especially the video is of the corn field is nice. Thanks!!

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Follow up questions: Do you guys use the new Pixhawk 2.1 or still the old one?
I know the APM2.8 that i have only runs ArduCopter 3.1.2 or so, and i can see that helicopter support was added quite short before that release. So i’m assuming that the APM2.8 is really not such a good idea to start with. Could somebody confirm this?

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I would go for a “old” Pixhawk , but buy it only from MRobotics, USA, https://store.mrobotics.io/category-s/113.htm

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Don’t use APM unless you are going to stay with it.
You will have to set everything up again when you upgrade to Pixhawk.

Pixhawk 2.1 is more future proof, no problem with support. It’s only pricier and may give you trouble using older hardware connector.
I’m using PH2.1 on my heli with no real issue.

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Any specific reason for buying it at that place? Also, the price difference vs a pixhawk 2.1 is very little.
It seems 2.1 is a lot better for vibration…

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I’ve been using regular Pixhawks and a 3DR Pixhawk Mini on one heli. The Mini can only run AC3.5 and newer. I haven’t had any problems with any of those. I think the PH2.1’s are getting easier to come by now. The early supplies were bought up as soon as they hit the market and demand couldn’t keep up with supply. I don’t know if a PH2.1 can be put on a 450 though. It is a pretty big unit and there’s not a lot of room on a 450 to mount stuff.

However, the APM will work fine on your 450 with AC3.2.1 for experimentation and learning. You may not be able to carry the settings forward. But the experience in learning how to set up a heli will be worth its weight in gold. And wouldn’t cost you anything. Sounds like you have everything there to do it. Especially if that 450 is a flybar model. Flybars are super-easy to set up from the ArduPilot side and fly good out of the box. Flybarless heads are a little more of a challenge.

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Maybe this will spark your interest, Ruben.

This is a little Trex 500 that I modified for long flight time. It can fly in 30km/hr wind no problem. About 4.1kg takeoff weight. Can easily lift 50% of it’s own weight in payload and fly away with it at 10m/s flight speed. Has a most efficient cruise speed of 10 m/s. Top speed of 22 m/s (running low headspeed). And will hover for 30 minutes and fly at 10m/s for 34 minutes.

Bought the helicopter in pieces, crashed, for $90. I have less than $500 in it and it’s a really fun little heli to fly. I was a little rusty on the collective on this one - hadn’t flown it for awhile. My wife flies it a couple times a week. It’s kinda her heli now I guess (so she tells me) :grinning:

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Hi Chris,

That looks like a very, very nice build. You make it look very easy!

You’re absolutely right that i have everything to start testing with the 450. I’m considering it very heavily. I guess i still want to do a few tests with the Quad that i have before taking the flight controller out of that. And, i also think i need more practice flying the actual heli. At the moment, i’m slightly too scared of crashing it :slight_smile:

It’s going to take a lot of time, which is not helped by the fact that i need to drive out to a field to fly something.
I really appreciate the amount of effort you’ve put in to responding to my questions, but i really know that i need to spend time myself on things now, before posting more questions and/or problems!

Thank you a lot!

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You can not crash it.
Especially with 450 size, it’s very easy to make a training gear for smaller heli.
Once you get gains dialed, it will be as easy to fly as multirotors.