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Speed Controllers And Batteries

Multi-Rotors, First-Person View, And The Hardware You Need
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Electronic speed controllers (ESCs) are used in many R/C applications. They translate signal to electrical supply. On a multi-rotor, every motor gets its own ESC, each of which connects to the flight controller. After computing the inputs, the controller directs each ESC to adjust its speed in order for the craft to perform them.

TBS Bulletproof 30 A ESC setTBS Bulletproof 30 A ESC set

ESC refresh rates vary. For multi-rotors, given the balance of multiple motors critical to the craft's ability to stay airborne, high refresh rates are more important than many other hobbies where ESCs are used. 

In essence, we're talking about programmable microcontrollers, and they employ firmware to define and carry out their tasks. In the world of multi-rotors, SimonK is the supreme ruler of ESC firmware, creating revisions optimized for multi-rotor use, stripped of irrelevant features, and sporting refresh rates as high as 400 Hz or so. ESCs can be flashed or purchased with SimonK's optimizations pre-loaded.

The only other major factor to consider is an ESC's maximum current rating, which must exceed the current draw to each motor. Generally, 30 A for medium/large quads and 10 to 12 A for a small quad is plenty.

Clearly, those are high current draws. But such is the nature of multi-rotors. A medium-sized hex can easily pull 40 A on a steep ascent. As a result, hefty batteries are a necessity for decent flight times.

The industry standard is lithium-ion polymer (LiPo) batteries. Relatively lightweight, compact, and offering high discharge rates, LiPos are well-suited for multi-rotors.

2200 mAh 3S 35C Turnigy Nano-tech LiPo2200 mAh 3S 35C Turnigy Nano-tech LiPo

Ready for another set of specifications? There are three to consider as you start perusing the cyber-aisles of LiPo batteries. The first is voltage. A single cell supplies a nominal voltage of 3.7 V (4.2 V at full charge). Each additional cell wired in series adds 3.7 V to the nominal voltage of that pack. Cell counts are denoted by the number of cells followed by "S". A 4S LiPo, therefore, is a battery of four 3.7 V cells at a summation of 14.8 V.

LiPo packs also have C ratings that indicate the maximum rate at which a pack can be discharged, with C standing for capacity. A 20C pack can be discharged at a rate 20 times its capacity.

Capacity, therefore, is the third important factor. It's measured in milliamp-hours (mAh). Let's say our 20C pack has a capacity of 4000 mAh. Given what we know about C ratings, we can do the math and determine its maximum discharge at up to 80,000 mA, or 80 A. Similar to ESCs, you need a discharge rate that's higher than the combined draw current of your motors.

LiPos connected in parallel add to capacity (rather than affecting voltage). In turn, the aforementioned S notation is modified. A 3S2P arrangement, for example, consists of two three-cell LiPos connected in parallel.

Batteries do not last forever. They vary in cost, and the pricier LiPos typically last for more cycles than the cheaper ones. A pack will “puff” in its plastic wrap as it gets to the end of its rope. Excessive heat after use is another bad sign.

The best way to prolong a LiPo’s life is to follow the 80% rule. You should try to avoid discharging more than 80% of the battery's listed capacity (a maximum of 4000 mAh from a 5000 mAh pack, for example). Also, monitor voltage when you're flying, and land before reaching 3.3 V per cell. Voltage falls more rapidly as charge is depleted, and at 3 V per cell, you might drop out of the sky. Some flight controllers have protection mechanisms to help prevent over-discharge.

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  • 2 Hide
    gio2vanni86 , June 3, 2014 4:55 AM
    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.
  • 4 Hide
    Joshua M Below , June 3, 2014 6:13 AM
    I'd really like to see build costs.
  • 2 Hide
    freiss , June 3, 2014 7:46 AM
    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 Hide
    Steveymoo , June 3, 2014 9:07 AM
    So, how much would the components cost to lift a heavy DSLR with some decent glass? I is pretty curious.
  • 2 Hide
    es0 , June 3, 2014 9:23 AM
    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!
  • 5 Hide
    thechief73 , June 3, 2014 9:43 AM
    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.
  • 1 Hide
    HKILLER , June 3, 2014 1:14 PM
    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
  • 2 Hide
    rmirwin2 , June 3, 2014 1:50 PM
    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.
  • 1 Hide
    bluescrn , June 3, 2014 4:02 PM
    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.
  • 0 Hide
    bluescrn , June 3, 2014 4:20 PM
    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!)
  • 3 Hide
    none12345 , June 3, 2014 6:01 PM
    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.

  • 0 Hide
    DrBackwater , June 3, 2014 7:13 PM
    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.
  • 2 Hide
    JohnA , June 3, 2014 9:18 PM
    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.
  • 0 Hide
    quadcopterhq , June 4, 2014 4:40 AM
    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 Hide
    marraco , June 4, 2014 5:47 PM
    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.
  • 1 Hide
    w8gaming , June 4, 2014 7:14 PM
    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.