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Nov 27, 2012, 07:06 PM
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Originally Posted by Brandano
Canting the two rotors inward should have a negligible effect on stability. The dihedral effect works due to sideslip which causes one wing to have a higher AOA than the other. But it takes a pretty large translational speed for a rotor to start developing translational lift and be affected by rotor "dihedral".
The idea is that with the motors pointed outward (blowing air away from the wings) gives the whole platform more air to "sit" on in a hover. I call it dihedral, but I know the principle is not the same as on a wing.
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Nov 27, 2012, 08:17 PM
NoT iNtElLiGeNt

can i do like this, to connect both side engines(in pic)
Nov 27, 2012, 09:15 PM
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You'd need a very strong material that doesn't twist under load. I've tried a similar setup and had trouble finding something that wouldn't twist creating slop in the system. You also can not hook up the servo like that. The movement wouldn't be correct. There should be a small pushrod connecting the servo arm to another linkage on the tilting section in order to get full movement.
Nov 27, 2012, 09:40 PM
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Something like this is almost exactly what I tried. The rod material is the problem
Dec 21, 2012, 09:09 PM
NoT iNtElLiGeNt
can u tell me answers for following questions

1) calculating center of gravity for orbitary body?
2) calculating moment for multiple loads & orbitary body?
3) important topics in gyroscopic for RC's.
Dec 21, 2012, 11:35 PM
Registered User
Originally Posted by jyothibasu1k
can u tell me answers for following questions

1) calculating center of gravity for orbitary body?
2) calculating moment for multiple loads & orbitary body?
3) important topics in gyroscopic for RC's.
Multiple years of experience, eyeballing it, and lots of testing lol.
Cant help on the 3rd one. Just using generic helicopter hh/rate gyros. I don't have much experience in advanced stabilization and gyro boards
Feb 14, 2013, 10:22 PM
Registered User
Ok, so I've been refraining from using any stabilization boards, but........ I've been looking into the multiwii and considering taking the plunge and getting one. The capabilities are amazing but it'll take some time to learn the pogramming/setup. I've already been searching around and found a VTOL code that I think a few others have used with success?
Seeing all of the successful VTOLs lately makes me want to finish mine. I still think the tricopter approach for hovering is the best, easiest, and cheapest to achieve. (FoamandTape's chimera VTOL is a great example )

Stay tuned, but learning how to use and program the multiwii board is going to take a bit of time
Feb 14, 2013, 10:37 PM
Retardedly intelligent
foam and tape's Avatar

A wise choice! that's what we're here for If I can figure it out anyone can.
Feb 22, 2013, 03:56 PM
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Trying to get my radio re-configured for when the stabilization board I ordered gets here.... Not the multiwii........Yet. But it's just a simple 3-axis stabilization board for now to test with.

I ran into a snag though while trying to program one of the basic mixes with my dx7 and was wondering if anyone had any ideas or could help.
I'm trying to slave aux2 to the elevator channel- So the elevator FF surface is on a different channel than the rear motor which is mixed externally with throttle for pitch control in a hover. The elevator channel uses the pre-programmed dx7 flap-elevator mix to allow the elevaor surface (that has the rear motor mounted on it) to swing down when the wing mounted motors tilt up, turning the whole thing into a tricopter. Then the slaved aux2 channel (used by rear motor) allows for pitch control through elevator stick input.
I need to be able to toggle the elevator channel, from responding to stick input to not responding (in hover), all while the slaved channel to elevator still functions 100% of the time. I thought this would be simple by using elevator dual rates to go from 100% to 0% travel. This toggles the elevator channel on/off just fine, but the slave channel that needs to stay responding to stick input does not respond as well.
Anyone at least understand?

Feb 22, 2013, 04:15 PM
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v22chap's Avatar
Not sure if the dx 7 has it ,,but with most other computerized tx's you can disable certain ch's and or mixes with the 3 position stunt switch ,,,which might do what you want ... if I understand it right .

I also have used multi -point aux ch's to mix in a control to that I want it to work only part of the time ...
you do this by keeping the muilti point curve at 0% across the graph (or the % curve ) until you want it to work and then you start raising the percentage .

Like I mixed flaps to my conversion lever ch .. and in the first half of the lever travel the flaps stay down ... then in the last half they move up to normal position as the conversion reaches airplane mode .
Hope that made sense
Last edited by v22chap; Feb 22, 2013 at 04:21 PM.
Feb 22, 2013, 06:34 PM
Registered User
There's no option (that would help) to disable channels or mixes.. But you did get me thinking and I've figured something out that should get me what I need.
Instead of being lazy and keeping the elevator channel the control surface channel, I'm going to have the rear motor (constant) be on that channel. Then aux will be slaved to the elevator which will serve as the elevator surface itself. Basically the reverse of the setup I was trying to get to work earlier.

The pros of this setup:
-Mix (rudder dual rate) switch turns aux to elevator mix on/off effectively disabling/enabling aux channel from elevator stick input
-Elevator channel is ALWAYS constant. Perfect for the needs of the rear motor

-Previously used elevator-flap mix (default in dx7) is now useless
-Have to reconfigure flap-elevator system by mixing aux to each different flap position to get it nearly identical to the way it was before :/

I've tested this, and it will work and do what I need, but it will not be ideal. Gonna be a few hours of programming before I get it perfect...

Thanks v22chap!
Feb 22, 2013, 08:56 PM
Registered User
Just got everything configured- New mixes applied and previous mixes affected have been fixed. Everything is running perfectly in the radio just as it was before. Only now it has the toggleable elevator surface
Gonna hook the airframe up and test flight controls sometime tonight or tomorrow to confirm that the programming works as it should.
Last edited by rcjetflyer2; Feb 22, 2013 at 09:24 PM. Reason: Typo
Feb 23, 2013, 11:21 AM
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v22chap's Avatar
Good luck on your test flight .
Feb 25, 2013, 09:46 PM
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Ran D. St. Clair's Avatar

It looks like your current configuration is close to working and has a good chance of getting you where you want to go. I have a couple of suggestions.

1. Buy a KK2 Flight Controller board from HK.
At $30 plus shipping they are pretty cheap, and it has all the gyro's and accelerometers you will ever need in one package. I am not saying anything bad about the various other flite controllers, they have their advantages, but the KK2 is plug and play, with a push button LCD programming interface, so there is no code to download, just start pushing buttons.

2. Tape a piece of foam under the nose of your craft to raise the nose about 10 degrees when it is sitting on the ground. That will balance out the forward thrust of the rear motor, which is not pointing straight down, and allow you to get off the ground into a hover. In your current configuration you are immediately into slow forward flight and then you run out of room. This would be no big deal if you jumped it up to 3 feet right from takeoff, but I understand your desire to gently get into a low hover so nothing gets damaged.

3. If you go with the KK2, or pretty much any flight controller, you will need to feed unaltered roll pitch and yaw into the flight controller. The KK2 then has 8 outputs that you can use to drive your three motors and up to 5 more servos. It has built in configurations for tricopters and much more. In your configuration the only servo the KK2 would probably drive is the tail rotor twist for controlling yaw. Your tilt servo will probably bypass the KK2 and you can drive it with flaps set for slow. The other servo's for elevator and ailerons would be driven direct from the RX.

4. If I were you, I would separate the tilt of the rear motor from the elevator. It might seem like a simplification to tie them together but it actually complicates things. Then you can have all your motors tilt together controlled by the flap switch and you don't have any mixing problems.

The elevator and ailerons are then just normal serfaces and simple to manage. They don't need to be controlled through the KK2 board, so you can just use a Y harness from the RX.

You don't need a rudder since the roll input through the motors will become yaw, and your dihedral will do the rest. You do need vertical stabalizers for forward flight, but I would just glue them onto the ends of your horizontal stabalizer. You actually don't need ailerons either, the differential motor thrust and dihedral will take care of that as well. Ailerons might still be nice though.

I haven't seen the mechanism in detail, but I gather your rear motor can both tilt down and back for forward flight, and also twist left and right for yaw control in the hover. The KK2 will control the yaw servo for you. When the motor is rotated back for forward flight the twist for yaw control will do nothing, so their won't be any bad control interactions. (Depends on how the mecanism works.)

Once you separate the rear motor tilt from the elevator you will be able to make the mechanism tilt straight down if you want. That will allow you to hover with the fuselage level. In forward flight the motor can point straight back, and doesn't need to go more than 90 degrees total, so it is no problem driving it with a servo.

If you use a flight controller board, you will want to turn the "I" feedback loop off and use only "P". You will still be able to hover just fine that way, and when you get there we can help with some of the fine tuning. Turning the "I" off is important to avoid nasty control interactions that can mess you up in forward flight.

You are actually very close to being able to hover, which means you are close to slow forward flight, which is actually even easier. I assume making it fly as a regular airplane is trivial, so you are almost there.
Feb 25, 2013, 11:17 PM
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Ran D. St. Clair's Avatar
I just noticed. You are going to have a big problem if you ever try to go into forward flight. It looks like the CG is near the trailing edge of the wing, which is where it needs to be to have all three motors evely loaded in hover mode. Problem is, it will be massivly tail heavy in forward flight.

The simplest solution is to make the horizontal stabalizer larger, much larger, like 60% of the area of the wing. That should allow you to keep the CG roughly where it is. The motors tilting forward will help move the CG forward a little as well.

For your next design (I am assuming there will be a next design) think about where the CG needs to be in all flight modes.

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