Need advice about RC options for ultralight paper airframe project

Discussion in 'RC Aircraft & Watercraft' started by liftline, Sep 29, 2010.

  1. liftline

    liftline Member

    My 1:48 Spitfire is low wing and incredibly stable just from the natural dihedral that results from it's elliptical wing. Only gets aerobatic when I dial that in!

    Been looking into coil actuators; all the ones I've seen on the web seem set up with little lever arms, like tiny servos. Have you ever seen any built directly into the control? Micro fly by wire! That would be way cool.
  2. schorhr

    schorhr Member

    Actually a lot of models work that way

    Some built them with electronics from a $2 servo, some buy them in a kit
    For real light models muscle wire is certainly woth a look too.

    Fly-by-wire: Heh. If it can lift long wire :) I think that could be critical with a smal lmodel
    At $32 for a radioset, I would not bother.. still requires electronics ;-)
  3. liftline

    liftline Member

    "Fly-by-wire" in USA aerospace terminology is a control surface that is controlled electrically, rather than by the older mechanical or hydraulic means. Like what's used in the F16. You command of English is so good I get a bit careless with the Americanese jargon!

    Anyhow, I'm leaning towards purchasing the following austere system, based upon your recommendations. Just 1 servo and a speed controller.

    2 g hobby king motor :

    4 g speed controller

    1.7 g servo

    1 cell battery 3.7v battery, 4 g

    Any compatability problems with the 6 channel hobby partz 2/4 ghzRC system?

    All the onboard stuff weighs just over 8g, which is what I have to ballast the model with anyway to get the CG in the right. The weight is "free" so to speak. Not exciting, but a low risk proof of concept prototype, where I can get some experience with small scale RC building and flying and get some good video of the airplane actually in the air.

    If flight test go well I'll upgrade to 3 axis control.
  4. schorhr

    schorhr Member

    Thanks :)
    I only once saw a video with fly-by-wire, the old "pioneer" model plane flight, using cable remotes :)

    The servo will work with one cell according to the description.

    If you want to make sure, this speed controler is 2g AND has a voltage booster:
    So there will not be any low battery reciever glitches... Though you could ask someone on the forum. I do have the v1 hobbyking radio, which is probably identical with the hobbypartz-model, but as I do not have any 1s setup I can not really test how it will perform under load in flight.

    seperate boosters are available, but heavier (at least without stripping them)

    if you want to go ultra-light, and with such a model even a crash is not dangerous, you could try to fly without a booster or just ask in the Hobbyking forum prior to ordering.
    Here is the lighter ESC without booster

    As I (think I) said earlier, I am no micro-pro, but I do know my way arround the components, as I want to build some micro stuff too once I get arround to it. But if you use the boost-esc, you should be all set.

    You could get a cheap $20 charger off ebay that should do the job and is suitable for other projects as well (100mA and up for charging, max. 6 cells, lipo and others).

    +AC 12v 1A minimum to avoid problems ($3-5 Wii AC/DC from ebay will do, or old printer/laptop ac/dc, or modified old computer atx powerbox; Chargers for the b3/b6 charger clones with the correct plug are available at $8-10) though these small packs might work with less amp, and input is specified for 11-18v

    Alternativly those small batteries are used in lots of planes and you could get a cheap wall charger with no display and fancy electronics. I saw they total up to almost $10, so getting a charger thats at least a bit better is the way to go.

    cheaper batteries if you need to order spares speratly and it would cost more to pay the hobbyking shipping; No name, but okey for the 2g motor I'dd say!
    as the ones at HK are 11g they are ideal to order along though.

    As for cables: Ebay is sometimes cheaper, espeically if you calculate in the shipping (as i usualy do)

    As for charging multiple, you could get , but then they charge unbalanced. Not recomended, though these tiny batteries are cheap and you should not charge unatended anyway (and on a fireproof, non conducting surface....)
    There are some adapter boards that will hook them up in series and provide a balance plug, but I could not find a (cheap) board with the JST-XH, and if neccesary you could wire it using the cheap cables off ebay.
  5. liftline

    liftline Member

    Great tips Schorhr, you certainly do know your way around components. Psychic too! I was about to ask you about battery chargers but you read my mind.

    So, At 2g and $10 US, what's not to like about the speed control with a booster? Can't actually get any ultralighter with my Se5a and still achieve proper balance, at least with the minimal rudder throttle, so the .7g booster speed control doesn't buy me anything. Might look more attractive when I start packing additional stuff into the airframe to get 3 axis control.

    I like the idea of using string to connect rudder to servo, it will look right on Great War aircraft even if not strictly scale. Same for the elevators, when I get around to them. Very thin steel wire torsion rods are looking attractive for the ailerons, they would even strengthen the wing a bit.

    Why are 2 servos recommended for ailerons? Is it because it makes it easier to trim them to neutral roll. I can see how that might be difficult with 2 ailerons slaved to the same servo, but that's just my guess. Maybe it's just power?
  6. schorhr

    schorhr Member

    Yikes, I just discovered a flaw in the setup:
    The servos work most reliable with 4.2 and the reciever with 5v.
    So the servo might have too much volt (hk product discussion suggests a resistor) and the reciever might cause issues before the cell is "empty".
    It is wierd that I was unable to find any discussion on the matter... neither at the hk reviews, discussion nor forum, and not on rcgroups either.
    Best would be to make a new thread.

    HK has a few great chargers too, but a bit more pricy. With those cheap devices it won't hurt to upgrade later and sell the used one... some might even apreceate if they can buy it within the usa and you may get close to the original the price ;-) WHen I started I made the mistake of buying a overpriced charger with features I never used, and now it's useless as it can only charge nicds.

    If you control ailerons with a single servo, you can only do rolls. Delta planes with ONLY ailerons use two servos: when tilting the ailerons both in the same direction, it takes the function of the elevator. With mixing (as module or built into most modern radios such as the cheap one) you can then do rolls and controll height. If rolling and pulling up, the mixer then calculates the right angles.
  7. liftline

    liftline Member

    Guess some more research is needed, I'll ask around concerning voltage compatibility. Right, two servos for controlling elevons like the F102 or F106 or Mirage. Or like my big ol' display Saab Gripen, the only delta in my fleet to date. Good time to ask about very tiny ducted fans though - any knowledge of them? Might be some physics limitations due to viscosity? I really don't like putting props on model jets - it upsets the delicate balance of the universe IMHO.:wave7:. I do have a paper jet design somewhere, I hope, of a SAAB Tunnen (sp?) "barrel", a rather tubby little fighter of the 1950s, roughly similar to the F86. Built it with a ducted fan in mind.
  8. schorhr

    schorhr Member

    Yes, ask arround- but seems like the esc is sold out atm anyway- so you could just try how low the reciever will go ;-)
    maybee you could just solder a diode or resistor into data to prevent harm and hook up the servos to the cell directly...

    No clue about ducted fans;
    I guess you can check rcgroups or just experiment with the 2g BL, perhaps an inrunner (more speed though, not slowfly, and I don't think they have one smaller then 5g... Even with that the main problem would be the diameter of the prop needing to be bigger then the motor for airflow, so the 30mm duct systems are the smallest with stock components.. Perhaps you could just fake it somehow, like putting a larger ducted into the body and non functional ones on the wings).

    30mm ducted for 2 cells
    look at dx they have some 30mm housings and stuff as well -- quote:
    ***Look around here in the threads, there are some 20 and 15mm EDF projects using handbuilt impellors and custom wound motors.***
  9. liftline

    liftline Member

    The smallest ducted fan I had been able to find was 49mm - too big even for my Tunnen. Thirty is doable and 20 opens up real possibilities...if I can just figure out a working RC rig. Engineering wouldn't be fun if it wasn't hard!
  10. schorhr

    schorhr Member

    Start off with some propeller model and then go to 30mm ducted but thats pretty bulky for a micro rc plane... sounds like lots of work to get a doable customized solution.

    Other ideas:
    -Fake ones and a folding prop that is not visible when landing
    -Just use a regular prop (perhaps acrylic) inside a tube so its somewhat scale and only visible on closer observation ( quick shematic sketch )

    The small motors are probably the last innovations for a low price... There are special vendors that make even smaller ones, but they are very pricy...
  11. liftline

    liftline Member

    The more I look, the more I like that Hobby Partz rig you came up with. Gets good reviews so far as I've seen. Maybe just go to a 2 cell Lipo and adjust excess voltage with some resistors. Weight will go up, but not a show stopper.

    I just wrote my official introduction to the Zealot board (only a month late) and put out a call for second opinions from other micro experts out there. Still, I may be pushing the limits with my specs.

    Good news about linkages, prototypes have been surprisingly easy to engineer for my control surfaces. The way I engineered the hinges make it very easy to use simple, cheap torsion rods bent from thin wire, maybe even plastic. I would like to say I planned it that way, butwa really just luck.
  12. schorhr

    schorhr Member

    Sounds good--- I am sure the other issues will solve easily :)
    Good to hear the construction works out... I am certain you'll make it fly. Just go with the single cell, the boost esc and then drop the voltage for the servos, I think that will be the lightest option... or ask some people who own the t6a type 2.4g radio if they have issues with one cell only.
  13. liftline

    liftline Member

    All the RC stuff is on order, except for a basic lipo charger that will get me going. I'll have 3-7 shipping days to mull over control linkages and motor mounts. Weather is going to close in soon so I'll need to find a big gym or maybe sneak into one of the local covered sports arenas. Paper models hate snow worse than they hate rain

    I'm certain I can get this bird to work - maybe not on the first try, bu that's what blooper reels are for. I'll also need to find a skilled videographer to document the triumphs and tragedies announce1
  14. schorhr

    schorhr Member

    Sounds like you're ready to go then :) I suppose you own some (simple) soldering equipment? I forgot to mention that some things such as battery/esc plugs are not standarized and you might want to get some cheap cables off ebay...

    For video: Go get a $8 key spycam at ebay and a inexpensive 1-2gb microSD... Or $18 video sun glasses...
    Decent video for the price, plus the keychain spycam can be stripped to 5g if hooked up to the aircraft's battery... neat on-board cam !
    I experienced some problems on my micro heli with recording, but a capacitor might 'even things out'.

    A gym or so would be nice.... maybe there's even allready a flying club?

    What equipment did you choose? I'm certain it will work out... building is half the fun anyway, hehe.
  15. liftline

    liftline Member

    Ordered the HobbyPartz 2.4 6 channel. Good price, and gets good reviews. A no brainer.

    Went with the 2 gram hobby king motor
    Bought the 4 g speed controller from hobby king - oops. my mistake, should have ordered the 2 g one with booster. Too many numbers on my set-up notes, I chose the wrong one! Hope it works, seems technically in spec but it may not. Hobby Partz already E-mailed me that my order has shipped. They are fast - maybe because they are over the international date line and know what I've ordered a day before I do. Or something like that.

    Servos are a crap shoot too, bought 3 of the 1.7 g ones, which may be a bit overjuiced, but I should be able to fix that with a resistor. Dirt cheap, so not a great risk.

    And a one cell lipo battery to round things out. 2 actually, so cheap why not a spare?

    Still haven't purchased a charger. I should still have my soldering iron packed away somewhere..but can borrow from family if it's gone missing.

    Here's a great little find to go with my music wire torque/push/pull rods. Those little plastic beads they sell in craft stores make great guides/bearing for the steel rods. Light, tiny, pre-drilled. A lifetime supply costs about $3 US.
  16. schorhr

    schorhr Member



    Happens. If running the rX on a single cell is a problem, you can still order the 2g, and use the other for future projects... no harm done at those prices ;-)
    If it has not shipped, you could still ask them to exchange the part... Occasionaly support actually responds in time ;-)

    Soldering: Worst case: A $4 soldering iron, hehe.

    Neat idea with the beads! It's allways good to just look around what can be used instead of expensive model parts :)
  17. liftline

    liftline Member

    Looked into those sunglasses-they look much better than I thought they would. I sort of envisioned Groucho Glasses - the ones with the fake nose, eyebrows and mustache. :cool:

    Someday it might be nice to pull one of those tiny lens units out of the housing and fix it in the open cockpit looking over the Aldis Sight. Gun camera footage!:eek:

    In the early documentation phase I'll just borrow my brother's video camera and have him aim shoot while I try and fly. He's got a good unit and should be able to get some decent detail. Some of what I get at the big annual WWI fly in at Wright Patterson AFB, in Ohio is amazing! The silk scarf on the 1/8 scale pilot. The headset in the leather helmet of the pilot flying the Fokker Triplane Replica.

    About the mis-ordering, no big deal. I'll just wait for all my other mistakes and omissions to float to the top, put in a new order and save on shipping. Hobby King is quick and send me E-mails in what seems like nano seconds. Hobby Partz is a bit more reserved.

    Even though I ordered 3 servos I'll be using just one on the first build....the "training wheels" phase of development.
  18. schorhr

    schorhr Member

  19. liftline

    liftline Member

    All airplanes pump (porpoise) a bit during flight. The vectors driving pitch are in dynamic, not static equilibrium. The P51 was notorious for porpoising badly in a full throttle chase - throwing aim off and saving many an FW 190 pilot. Excess up elevator tends to magnify the problem. This is what gives me palpitations whenever I glide test a new design - make that a new airframe! I want to set the elevators so that I tend to get mostly positive main wing angle of attack during each oscillation, but not so much that I induce a stall as angle of attack maxs out. It helps to hold a model into a brisk breeze before the first flight - I can often feel the stall and adjust the elevators down a bit. That said, I test over high grass just in case. Once I get a stall free glide I then dial down the elevator to smooth the line of glide.
  20. liftline

    liftline Member

    Bottom line, I'll be thrilled if I can use the throttle so that the phase 1 Se5a porpoises around an ascending, level or descending line of flight. Plus banked turns induced by the rudder, with help from dihedral. This will match my RC piloting skills nicely. Have no fear, the plan is for full 3 axis control "at a later date in development."

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