I'm designing a new quad or hexcopter, Ive got my basic design and I know what autonomous flight controls I will be using. I'm having issues figuring out what motor, prop efficiency. Ive searched different discussions on the matter, but they way it is explained is as though they are speaking to people that have been in the hobby for a while. I basically need heavy lift capable and longest flight time possible. I'm not so much looking for speed, or agility really, but that would be a nice feature. If anyone out there can help me figure out my power thrust needs, I would greatly appreciate it
designing and building multirotor
- Thread starter ahren
- Start date
chrismog
Silly old fart
Hey ahren,
You could try e-calc for the info you need............
http://www.ecalc.ch/xcoptercalc.php?ecalc&lang=en
You could try e-calc for the info you need............
http://www.ecalc.ch/xcoptercalc.php?ecalc&lang=en
Unless you have a full pilot license and a full endorsement for drones, YOUR DRONE'S LEGAL MTOW (maximum take off weight) WILL HAVE TO BE LESS THAN TWO KG (2.2 lb). That is including battery, camera, gimbal etc. THE FINES FOR TRANSGRESSORS ARE VERY HEAVY. So START THINKING ABOUT EFFICIENCY, NOT BIG WEIGHT!!!
The heavier the machine, the less efficient it will be. A hexacopter will be more safe and controllable than a quadcopter. If one motor or ESC will fail in flight, you will still be able to land the craft. For a 3-4 lb hexacopter, I would suggest to use 1200kv outrunners and 8" x 4" props. The battery could be a 11.1V (3S), 3300mAh, which will give you about 8-10 minutes of hiovering flight. I just give you an example: this is one of the hexacopters which I have designed and built. It is flying very well, using six Emax CF2822 motors, six SimonK 20A ESCs and a CC3D flight controller. The camera is a Xiaomi Yi with a linear lens. On this one I started with three blade props, but I found that two blade APC thin electric or multirotor props are far better balanced and more efficient. REMEBER: VIBRATIONS ARE YOUR ENEMY! YOU MUST DO YOUR BEST TO AVOID THEM.
Cheers from Bruno
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Thanx guys. I am a commercial helicopter pilot and am familiar with the latest FAR/AIM. My project is not so much for fun, but I'm sure once it's complete it will be quite a bit of fun, but more so for research, i am just not familiar with electronic drive and the thrust ratios for this type of aircraft, but highly interested in learning, so keep the info coming, theres no such thing as too much help
moonpie57108
Member
Am I missing something, for hobby use as stated on FAA site - .55-55 pounds requires registration online, above 55 pounds requires a different type of registration.
moonpie57108
Member
- What are you calling heavy lift capable? 4 pounds, 8 pounds, 16 pounds?
- Long flight time and heavy lifting are almost polar opposites, something to consider because trying to do both makes it a very expensive idea.
Max efficiency is going to come from high voltage low kV motors, plan on 6s systems if not higher.
A good place to start is figure out how much weight you want to carry and with how many motors.
Say you want to carry about 3 kilos of payload with a hexacopter. (assuming you know this)
Say your frame is going to 1.6 kilos and can spin 18" props (assuming you know this)
Your RX,TX,Controls is going to be another 0.6 kilos (assuming you know this)
Lets figure a 6s 22,000 mah battery to add another 2.6 kilos (This a guess that may require you to come back and change after picking motors)
So before you have motor and esc weight you are at 7.8 kilos. Let use minimum of 2:1 thrust to weight for final build, so lets assume 4:1 off the current weight of 7.8 kilos because you don't know motor weight yet. This puts you at 31.2 kilos of thrust or 5.2 kilos per motor as a goal.
So jumping over to KDE site for some quick motor numbers, the first motor I clicked on is a KDE 5215XF-330kV. On a 6S system, with 17" prop, the motor is rated at 4.6 kilos of thrust at 30 amps to give you a max thrust of 27.6 kilos. This is close enough, the motor is capable of more but we will start here.
Motors and escs add another 2.8 kilos, so your take off weight is up to 10.6 so lets assume 12 kilos for whatever I am missing.
At 12 kilos weight, 27 kilos thrust, you would be running 2.25 Thrust to weight which might fit the bill perfect for you and your frame/motors leave some room to get up to about 2.75-3:1 by changing props and/or battery.
These numbers may not even be close to what your looking for but you didn't give much to go on. If this fit the bill for you, you then go into the above mentioned ecalc and estimate your flight time. Flight time comes back at x, is this acceptable?
Yes -done.
No - you can try getting there with more battery, but you will also have to look at bigger props most likely to counter battery weight, if you max out prop size for frame, then you looking for a bigger frame....and the cycle starts over.
moonpie57108
Member
To simplify that down:
- Pick your payload
- Pick a frame that can support the payload
- Pick your control systems
- Pick the large battery for your current voltage goals, if frame requires you can always run two small parallel batteries. A bigger battery will almost give more flight time but it is not a 1:1 return. Adding 100% battery could only 30-70% more flight time.
Then pick your motors based on prop size limit of frame, always give your self room for a fudge factor.
Its not a guarantee, but the lowest kV motors you can run on a given prop size that will produce the required amount of thrust, is going to get you fairly close on your efficiency goals. After that, most of your additional flight time is going to come from cutting weight.
- Pick your payload
- Pick a frame that can support the payload
- Pick your control systems
- Pick the large battery for your current voltage goals, if frame requires you can always run two small parallel batteries. A bigger battery will almost give more flight time but it is not a 1:1 return. Adding 100% battery could only 30-70% more flight time.
Then pick your motors based on prop size limit of frame, always give your self room for a fudge factor.
Its not a guarantee, but the lowest kV motors you can run on a given prop size that will produce the required amount of thrust, is going to get you fairly close on your efficiency goals. After that, most of your additional flight time is going to come from cutting weight.
Wow, thank you so much. This was incredibly informative, my expertise is rotory wing aircraft and fixed wing. Most of my payload will be additional battery capacity. I was also thinking about derating motors, being able to produce the required thrust with less power. This craft isn't so much for a hobby, it is a learning experience, in the end, this will be a hybrid aircraft, capabilites of multirotor craft and fixed wing. It will have a dual edf system that i will have to account for. My original design in cad brought me to about 8ft wing span and just under 6ft in length. I'm also thinking about how to reduce the weight of the airframe itself, everything from helium filled tubing, fabric surfaces, carbon fiber, and microtruss structures. It's a slow process and a pretty big project for someone to take on alone, this is generally the job of an engineering and design team, but I'm enjoying the challenge
moonpie57108
Member
In that case, which are you looking to be the primary system? A multi-rotor platform might be over kill or under kill depending on how you look at it. A variable pitch rotor style heli head might be more of what you are looking for and would be a simpler tie in to a plane style craft.
If you got the know how and the equipment, I cannot imagine something much more fun than designing your own starting with the frame. Every once and awhile I have a random thought about doing my own small quad frames mainly because there is always something you wish was different. But I start looking at CNC machines, carbon dust, so on and so forth and I go back to googling for a new frames.
If you are derating the motors, it is going to be same thrust with more power or less thrust with same power.
If you got the know how and the equipment, I cannot imagine something much more fun than designing your own starting with the frame. Every once and awhile I have a random thought about doing my own small quad frames mainly because there is always something you wish was different. But I start looking at CNC machines, carbon dust, so on and so forth and I go back to googling for a new frames.
If you are derating the motors, it is going to be same thrust with more power or less thrust with same power.
I've got a 3d printer capable of many different materials so it's been fun designing different things. I really want to make both systems equally of use, but I'm fairly certain that the fixed wing function will end up being the primary, i just would really like to be able to retract the wings in and hover and maneuver as a quad at any time and then move back into forward flight seamlessly. My design is quite an eye pleaser as well. At some point in my build i will begin to post pictures, I'm just trying to keep my designs to myself for the moment
moonpie57108
Member
If the Flight Controller is capable of forward flight control (airplane) and multirotor flight, which I believe a PixHawk and its clones should be, it could be as simple as a toggle switch for which mode you want, trouble may occur through transition. (Did confirm, some setups are simply using a toggle to pick mode).
The PixHawk is open source, so it is capable of quite a bit even if it hasn't been done.
Google: Pixhawk Flight Controller and VTOL, I believe some people have already used this system to do this.
From briefly looking, you could use airspeed sensors to make it automatically switch between modes based on forward flight speed.
The PixHawk is open source, so it is capable of quite a bit even if it hasn't been done.
Google: Pixhawk Flight Controller and VTOL, I believe some people have already used this system to do this.
From briefly looking, you could use airspeed sensors to make it automatically switch between modes based on forward flight speed.