Multi-Rotors, First-Person View, And The Hardware You Need

Motors And Propellers: Heavy Lifting

The right electronics are a first step toward creating flight, but a multi-rotor isn't going anywhere without good old-fashioned practical physics to pull it upwards. Your choice in motors plays a pivotal role in the success of a capable setup.

This is also the point when specifications start to get complicated. You'll want to do some research before settling on the right configuration for your quad. And motors are expensive, making it even more important to consider the options carefully.

Motors used these days are almost exclusively of the “brushless” variety. That equates to minimal friction. A cylindrical shell of magnets rotates on precision bearings around a core of tightly and neatly coiled wire. The propeller is fastened atop. Many Tom's Hardware readers already know the composition of an electrical motor, but for enthusiasts dabbling in multi-rotors, the inner workings are unimportant. So long as reasonable care is taken and dirt kept clear of the bearings, brushless motors are famously reliable.

Tiger Motor MT-1306-10 3100 Kv brushless motorTiger Motor MT-1306-10 3100 Kv brushless motor

Motors are assigned various notations, the most consequential being the Kv rating. Confusingly, Kv does not refer to kilovolts in this case. Rather, it's a motor velocity constant denoting the revolutions per minute (RPM) that a motor will turn when a 1 V potential difference is applied with zero load. This number is important, as it defines a multi-rotor's flight characteristics based on specifications like battery voltage and take-off weight.

Also vital are the propellers you choose. The variety of props is arguably greater than any other component we discuss; materials, dimensions, and price span a mind-bogglingly wide range. Generally, cheaper props are less precisely manufactured and more prone to creating vibration. This applies especially to the relatively larger end of the prop spectrum, with differences becoming less perceptible for smaller craft. Again, some vibration can be acceptable, bolstering the case for less expensive propellers. But if you're flying a quadcopter with the intention of producing well-shot footage, expect to spend more money on propellers.

8x5 Graupner E-Prop8x5 Graupner E-Prop

It's worth pointing out that a majority of props are designed for airplane, though we're starting to see more optimized for multi-rotors. Graupner is a favorite brand amongst enthusiasts, and the company's E-Props, designed for electric power systems, are often cited as favorites. Other common options include Gemfan, APC, T-Motor, and RCTimer.

Gemfan 5x3 PropellersGemfan 5x3 Propellers

There are three simple measurements to keep in mind. The first is length, usually given in inches. The higher the Kv of your motors, the smaller your props need to be. Smaller props allow for greater speeds, but reduced efficiency. A larger prop setup (with correspondingly-low Kv motors) is easier to fly steadily, uses less current, and lifts more weight.

Frankly, the best way to gauge the right range for motors and props is referring to manufacturer recommendations if you're building an ARTF kit. Or you can simply compare the setups of more experienced builders. 

The second measurement, prop pitch, is less important, but of interest to more vigorous hobbyists. Prop dimensions are quoted in the form 9x4.7”, as a numerical example. The first number refers to the already-discussed length. The second is pitch, defined as the distance a prop would be pulled forward through a solid in a single full revolution, as if a screw through wood. The greater the pitch, the higher the thrust and necessary motor output. Typically, multi-rotors use props with pitches in the range of 3 to 5”. Lower pitches are more efficient, but lend a more sedate flying style.

Finally, we have bore measurement, which is simply the size of the hole in the center of the prop. This must be matched to the shaft of your chosen motors. Adapters are available to downsize a prop’s bore. Alternatively, some props, such as those produced by T-Motor, use a direct mounting system whereby screws secure the props directly to the motor head.

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16 comments
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  • gio2vanni86
    Great article, and quite an amazing beautiful video shot at the end. Been seeing these around, and have really loved the idea of filming at a elevated level. I actually do hope you guys do more of these. I am bookmarking this for future reference. Thank you.
    3
  • Joshua M Below
    I'd really like to see build costs.
    5
  • freiss
    Darn it, now you've piqued my interest. :-)
    As stated below, a rundown on build costs would be nice. Hey, you could even do a series of FPV articles akin to the PC builds...budget, mid-range, and enthusiast!
    2
  • Steveymoo
    So, how much would the components cost to lift a heavy DSLR with some decent glass? I is pretty curious.
    2
  • es0
    It would be awesome if you did build guides for different aircraft. I have begun building different ground based vehicles using arduinos and Pi's and would love to take to the skys next!
    2
  • thechief73
    Excellent article, nicely explained. Also glad to see someone in the media make a clarification from drones and multi-copters.

    FYI, DO NOT CALL THESE DRONES: Drones are for military use to kill people. These are, as the authors title states: multi-copters, multi-rotors, or RC model aircraft. By using the word "Drone" you give all the uneducated fear mongers and the law writers canon fodder to regulate this hobby into oblivion before it really gets a chance to take off. Some states and other countries have already passed laws that almost or outright make this hobby a CRIME!

    I have been in the hobby about a year now and I have to say it is so far one of the most fun and rewarding things I have done. I will be doing this until I no longer have the means to do so. I highly recommend anyone that is interested in joining the hobby to buy a Hubsan X4 or one of the many similar RTF mini-quad models. This is widley regarded as the best way to learn how to fly a multi-rotor.

    http://www.youtube.com/user/juz70/videos - not my channel, just really neat.

    Quote:
    So, how much would the components cost to lift a heavy DSLR with some decent glass? I is pretty curious.
    Just a few options: DJI S1000, SkyJib-8 Ti-QR, and CINESTAR-8.
    Quote:
    It would be awesome if you did build guides for different aircraft. I have begun building different ground based vehicles using arduinos and Pi's and would love to take to the skys next!
    Check out youtube, there are thousands of guide videos on the subject.
    5
  • HKILLER
    i would highly recommend these 2 for those who that don't want to go through the trouble of the build and already have an smart device such as iphone or android ones...
    http://www.newegg.com/Product/Product.aspx?Item=N82E16886113011&cm_re=parrot-_-86-113-011-_-Product
    and this cheaper model of it....
    http://www.newegg.com/Product/Product.aspx?Item=N82E16814998083&cm_re=parrot-_-14-998-083-_-Product
    1
  • rmirwin2
    There is one other regulating authority which is important to keep in mind for those seriously interested. In the US that would be the FCC, since transmission of quality RC and video signals over the available frequencies requires a Technician's class Amateur radio license. Many will find that a relatively easy thing to get that will also maximize the enjoyment of the hobby. Check in with ARRL.org, where you can get everything you need.
    2
  • bluescrn
    Great intro to multicopters. But for beginners, it's best not to start out with a serious $500+ quadcopter, as there's a pretty good chance that you'll wreck it on it's first flight...

    Do yourself a favour and get a 'toy grade' mini quadcopter first, such as the Hubsan X4/Q4 Nano or similar. These are cheap, loads of fun, can be flown indoors, are much safer than the big ones, and are a great way to learn to fly a multicopter. Spend a couple of hours playing with one of these, and you'll significantly reduce the time/money spent on crash repairs when you start flying a more serious multicopter.
    1
  • bluescrn
    Oh, and if you go down the ready-to-fly route (or even if you self-build), try not to be the next idiot losing control of a DJI Phantom in a location where they shouldn't have been flying at all ( e.g. https://www.youtube.com/watch?v=_U8iHn_2l0U )

    Stick to quiet and safe flying locations, be aware of wind, line-of-sight, and possible sources of RF interference. And don't rely too much on GPS/return-to-home - you might not have a GPS lock when you need it (or it might not have had a lock at take-off, to determine the home position!)
    0
  • none12345
    From someone who sells quads and has flown a lot of different ones.

    For most people(99%) id recommend something around $100. Nothing anywhere near as fancy/complex as this article goes into. You want something you can smash into things and have it usually survive.

    Stay away from anything infrared controlled, that stuff is just utter garbage.

    You want something around 4-5 inches on a side. Anything smaller that that ive had bad feedback on. Its just too small to keep orientation. The quads that are about 10-12 inches or so on a side are also pretty durable; but they arent as good indoors when they get to that size. Anything much larger and you will be breaking lots of stuff when you crash it.

    You can get a Blade nano qx for $90(70 without remote, if you already have a dsm2 or dsmx remote), and its quite durable out of the box. Shoe Goo the spaces in each of the 4 motor spars/guards on the frame and its nearly indestructible. It doesnt have gps features(you need a higher price range for that), but it does have a 3 axis gyro/accelerometers for self leveling, and it does a good job at it. Ive had a demo that customers have been smashing on for 6 months that we shoegooed out of the box and its only needed some blades from time to time, when dumb customers leave it crashed under full power letting the blades grind. And a couple motors after many dozens of crashes from about 80 feet up straight into the ground, when it was being flowing in manual/computer off mode.
    3
  • DrBackwater
    The concepts fascinating but with what Hollywood, and amazon have planned and all the different enforced policy's may result in who can use the sky's will almost need permits for most people in America, ironic given guns are reasonable to some extent when they should be abolished and smelted entirely.

    But the rc copters cool, and fun sadly the reality is, bureaucrats will rather see this burn then allow the public have access.

    Guy builds rc copter
    Guy adds unknown substance to rc copter
    Guy mounts go pro
    Guy goes perving
    Guy becomes a flying paparazi
    Guy flies it professionally into building and kaboom.

    How ever having a rc copter would be best suited that is if the bureaucrats get their chance at it.

    1 Seeing nature
    2 Movie making
    3 Visual effects
    4 The best selfies ever
    Well that's all I have for now.
    1
  • JohnA
    What an irresponsible article.

    You never mentioned liability. You hand waved any responsibility at all when you pointed out there haven't been any convictions.

    Read up. These things can and have caused serious injury. Do yourself a favor and join the AMA at modelaircraftdotorg. For 50 bucks you get a two million dollar liability policy and the legal guidelines you must follow to be covered. These things aren't fully automatic, and flying VR is NOT for beginners. I've been doing helis since the 90's, started RC in 78. The more noobs that go out and hurt people and annoy neighbors the more likely the entire hobby will be regulated out of any fun.
    1
  • quadcopterhq
    Great write up! I've been waiting for someone to do a detailed explanation of the technical side of quadcopters and other small scale UAS.

    For those who want to try out quadcopters without building your own, there are now a ton of ready-to-fly consumer models out there. For the low end budget, I highly recommend the Hubsan X4 line. For the mid range (or if you want to do any video), check out the DJI Phantom line.

    You can find more info and reviews on both of those here: http://quadcopterhq.com/best-quadcopters/
    0
  • marraco
    I expect a "best build for the money", for categories like high quality film, sport flight, distance covered (that needs GPS and fast phone), load carrying, automated repetitive tasks.

    Go toms! This is a new world to expand into in, and it can open the road to robotic applications.

    reading about a newer processor 10% faster than the older generation turned boring long time ago.

    Let's do other things with the hardware.
    0
  • w8gaming
    Surely permit should be required to fly these things. Otherwise why don't we just allow everyone to drive a car without licence? Or remove all car plate number from all vehicles? At least it should be proven that one is qualified to fly such thing, be responsible for it, follow certain rules, and can be identified and tracked.
    0