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Old Nov 29, 2012, 09:51 AM
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Freakazoid's Avatar
Roosendaal, Netherlands
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So, bicopters... Method to madness?

Ever since the dawn of multicopters Ive been fascinated by all the different shapes and sizes these machines can take on.
Since then I have tried just about anything from tri to Y6, from pocketsize to heavy lifters, and now it has come to this, the Bicopter.
A seemingly impossible flying machine with surprising capabilities.

I have previously dabbled into the world of bicopters by trying to create a flying sandwich,
but unfortunately that never panned out as there was an amount of servo jitter I could not seem to debug.
I suspect the project was simply too small for the servo resolution to handle a stable flight.
So perhaps one that nears a 2 foot span will have more luck.

Ive already sourced some materials to build myself a bicopter,
though I was hoping to learn some of the methods to this madness before I start taking the hacksaw to it.
Here's the list of things Ive managed to cobble together sofar, hopefully I can make it work.
  • I got a pair of tail assemblies off a spare parts list for this turnigy talon tricopter.
    It is made of alloy, double balljoint hinged for minimum slop, and is fully fitted with ball bearings.
    Its got a skid leg integrated in its design, which hopefully be part of a nice tripoint landing gear.
  • Motors are KDA20-26M ones.Capable of 750gr. thrust for roughly 13 amps.
    Not the greatest of champions, but Ive got too many of them laying around.
    I plan on swinging 3blade 8x4 props, should give 750gr. thrust @ 13A each.
  • ESCs are cheap Turnigy multistar 15A ones.
  • The controlboard is a nice little Jussi miniwii, fitted with MCU6050 sensor plus magnetometer.
    The latest 2.1 firmware seems more focused on bicopter settings so hopefully I will benefit from that.
  • Servos are Turnigy MG90 metalgear ones, they seem to be reasonably rapid and can swing their weight decently.
    That, and probably these things will get to eat a few knocks before finally flying, so sturdy gears is probably not a bad idea.
  • Purely for aesthetics, I managed to fish a protech alpha 180 fuselage from a friends attic,
    hopefully with some slight tail alterations this should serve as a handsome shell for my new gimmick.

So here are the things I still am in the dark about.
Lots of people seem to employ a forward swept armature which seems to be called oblique.
Though there are also a number of successful bicopters that don't seem to use such angled pivoting.
So I wonder, which one is best and why?
Also there's the matter of the tail structure. I do have the option to make it servo operated,
but should I bother with that? Or just go for ground adjustable?
And finally, how does one determine the best "span" so to speak, the distance between the motors.
The fuselage is 102cm long (although easily shortened), estimated weight is near 700 grams, if that has any baring on it.

So there you have it. If anyone has helpful tips, I'm more then happy to listen.
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Old Nov 29, 2012, 10:33 AM
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KAMAX-T's Avatar
Powell TN
Joined Jan 2008
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hey freak .... I am currently building a bi , based off of the gress platform...The gyro effect of the props tilted at a 45 degree angle , is what levels the craft...heres some info on his machines...

http://diydrones.com/forum/topics/bi...mment%3A420853

you may have already seen this , but it's good to know ?

Terry
also check on the'' nvader 600" build in areial photography
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Old Nov 29, 2012, 11:23 AM
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Haha I'm already on his forum requesting info about what he calls oblique control.
His design is actually what prompted me to go dig up some old glider fuselage.

So the trick is to get the motor axis at a 90' angle from each other as seen from the top?
I might try and mount the arms swept forward instead of bending the arms, if "obliquing" really has that much of an advantage.
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Old Nov 29, 2012, 11:53 AM
um.. yeah, I can make that fly
Carlos230023's Avatar
United Kingdom, Milton Keynes
Joined Jun 2007
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Hi guys, thought i'd chip in. Im also on the brink of Bicopter construction. Though I figure, go big or go home. my thoughts on design thus far;

These motors;
http://www.hobbyking.com/hobbyking/s...0kv_1300w.html
Hitec HS-5245MG Servos for plenty of gusto
Main bar will be 30mm square aluminium section
Motor mounts will be 3D printed (a very handy tool to have ) with a 5mm steel shaft, duel steel bearings printed into the motor housing, with geared teeth printed into the motor mount, and a separate gear printed to screw to the servo horn, that way I can vary the ration from servo to motor to get the best out of the servo resolution.
End caps for the main bar that hold the servos and the motor mount rod will also be printed.
DSLR tilt and roll mount to hold a Lumix DMC-GH2 cam.
two 3s 6000Mah cells ties togeather in series to make a 6s 6000Mah cell.

I was tempted to use variable pitch props as the yaw is done via motor thrust angle adjustment (as opposed to differential torque effect via differential throttle method used on quads) but trying to draw up a variable pitch prop adapter (and finding the props in the first place without just cutting normal props in half :P), figuring out a way to actuate the variable prop without dirlling a hole down the middle of the motor shaft all seemed like alot of fuss. so Ive put that idea on the back burner for another day.

Looking forward to seeing your progress

CJ
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Old Nov 29, 2012, 12:01 PM
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Goodness, will it have an inflight movie on its trip to the moon?
Frankly id be a bit scared powering up 2600 watts of experimental aircraft.
Be safe and be sure to have a camera rolling!

Are you planning to angle the pitch axis 45' ?
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Old Nov 29, 2012, 02:14 PM
um.. yeah, I can make that fly
Carlos230023's Avatar
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Not entirely sure about the pitch angle. I plan to cant the motor thrust line so that the bottoms tilt inward (spinners on top pointed away from each other) by between 7 and 10 degrees. Any more than that and you start to sacrifice lifting power. I've done plenty of mini quads and mid sized gopro bearing quads. I was looking to mount my DSLR on something. Looked at a hex but I figure less parts means less to buy and less to replace when it all goes south. Two servos and two motors sound good to me. That and I like the look of them. I like that I won't have two arms in front of the lens.

Oh yeah. I'm planning using the KK2.0 board. It does a good job on the 3D printed mini quad .

CJ

P.S. maiden flight is gonna have an 80 meter exclusion zone :P.
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Old Nov 29, 2012, 02:28 PM
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The armature blocks I got are originally meant for a tricopter that can have its arms swing back,
so I guess if I get a little creative on the CNC cutter I can experiment with it fairly easy, given I can balance my battery far enough.

KK2.0 are on sale right now btw, 19 dollars.
I still have a little mini multiwii laying around, so I might as well use it.

And yeah, better tie or weigh that thing of yours down, cause 2.6kW is gonna want to GO some places.

Ultimately id like to use mine for FPV too, technically it should be able to lift my gopro, though im gonna take it in steps.
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Old Nov 29, 2012, 02:38 PM
um.. yeah, I can make that fly
Carlos230023's Avatar
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Oh mine will defiantly be FPV ready. It's more or less all I fly. Going in circles LOS is fun for a while but not half as good as FPV. Much easier to fly a multirotor FPV anyways. I see when you mean about swinging back the arms. Just be careful that it doesn't throw off the motors tilt angle too much or you may get adverse yaw and pitch effects.

CJ
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Old Nov 29, 2012, 02:44 PM
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About the tilt angle, that's what im trying to pinpoint now, one says 45', the other 7 to 10', so whats the proverbial butterzone?
If anyone knows this, please be so inclined to tell us.

And im gonna fly my bicopter normal LOS first, if that works out ill think of ways to slap on FPV gear.
Meanwhile my quad and Y6 will keep me amused, its not my first FPV rodeo.
And totally, multicopters in FPV are 10 times easier, my friend kept fussing with scared little hovers,
strapped a camera on it and let him have a go, flew off right away.
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Old Nov 29, 2012, 02:49 PM
um.. yeah, I can make that fly
Carlos230023's Avatar
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Care to post a pic of what your thinking with this tilt angle? I'm struggling to imagine on which plane the tilt is applied to. Though 45 degrees is alot to add to anything.

CJ
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Old Nov 29, 2012, 03:01 PM
um.. yeah, I can make that fly
Carlos230023's Avatar
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This is what I'm thinking of (apologies for the crudity of the design, it was a 5 second mash together). to the motor axis of rotation angled toward each other at the tops by about 7 degrees.

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CJ
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Old Nov 29, 2012, 03:58 PM
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Heheh sorry, I should have been a little more clear about that.
Its surprisingly hard to explain with just words, so have a look at this video instead:

nVader 600 2012 (3 min 9 sec)


See how the motor axles point outwards when sweeping forward, and vice versa?
The pivotpoints on which the motorpods sway, are not parallel to the fuselage.
This is apparently called an oblique tilt rotor system, and im trying to figure out the advantages of it.
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Old Nov 29, 2012, 04:12 PM
um.. yeah, I can make that fly
Carlos230023's Avatar
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I cant see that it would help all that much, when yawing, the craft is relatively unaffected. But in forward flight the two thrust lines intersect at the tail (which is at a silly angle, any airflow over it would put the tail plane into an instant stall, unless he got enough forward airspeed to pass the stall speed and laminar flow, which would make the bicopter pitch down violently!). The differential thrust facing each other is basically wasting motor power sending it left and right at the same time. If anything this would create turbulence which would adversely effect stabilisation.

Just my 0.02 anyways :P.

CJ
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Old Nov 29, 2012, 04:24 PM
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Right, thats what I was thinking! It basically makes two motors fight each other doesn't it.
But Ive seen several "big shot" bicopters using it, so hence the title of this topic.
I dont get why one would angle the motors like that.

Here's a sloppy little machine that seems to cope entirely too well with parallel angles:

VTOL RC AVATAR SCORPION Prototype model2(MultiWii Bi-Copter) (2 min 43 sec)


So if that works so well, why do some people put so much effort in making a handlebar frame?
Maybe were looking at the holy grail but we have no idea?
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Old Nov 29, 2012, 04:30 PM
um.. yeah, I can make that fly
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Or perhaps someone only had handle bars to hand when they built one, and everyone thought it was a super secret. I know angling the motors thrust line inward as i showed earlier on larger multirotors helps slightly with level stationary flight, it also helps decent wobble when passing through your own prop wash as its slightly offset. But I cant see how this would help, God only knows why they went with a 45 degree angle, seems pretty extreme to me.

Well whatever everyone else is doing, Im going with parallel thrust lines when in forward flight :P.

CJ
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