Tandem/Tilt-Wing 4 Rotor Heli - RC Groups
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Nov 03, 2005, 02:50 PM
Registered User

Tandem/Tilt-Wing 4 Rotor Heli

I am working on a 4 Rotor Tandem/Tilt-wing. It is in an "I" formation.
Each Wing is connected to a Hitech 5995TG with 400+ounce/inch torgue 180(eventualy need 270) of travel. Imagine the aerobatics with this guy.

4x Hitech 5995TG servos for wing rotation.
4x Custom 8-10" Carbon/Glass Servo arms
4x Cemech Marathon 200HT
4x Twenty 2100mah 3cell LIPO
4x Aero Naut 13x8 Folding prop(acts as dampened rotor head)
4x C.C. Phoenix 25
So fare I have around $1,500 into it without radio.
Made with glass covered Loki Flying Wing Kit(Viper Hobbies AZ)(pink foam glass & carbon reinforced)

I will have photos in a couple days or so.
UPDATEHear is a draft of the rough design)

* Each wing Rotates Independantly 180(goal is 270).
* Ultra Low speed Half hover/Half flight
* Can Land in grass brush or on trees.
* Can Lay Flat after landing and hide in grass/brush, then it can stand on end to gather intelligence and lay flat again.
* Can walk like 4 legged robot.
* Wings easily remove for compact transportation (backpack size)

My free flight prototype glided very well so the design is airworthy. I just need enough thrust fromt the motors without gobbling up the batteries for VTOL.
This may be a very fast model and highly agile(maybe to agile).

I have the airframe 80% built.
The hard part will be finding a Remote Control that can do 8 channels mixed with each other in the way this requires.
I will have to have a hover mode a flight mode.
I am thinking about JR's top of the line remote or Futaba's?

I am looking for a very lightweight 3-4oz outrunner motor that has 45-55 ounces of thrust and has very high efficiency 85% would be great. I doubt that my Cemech Marathon 200HT will live up to its specs but I could be surprised.

Any Suggestions On Rotors or Props would ROCK. I am using a folding prop to simulated a dampened rotor head (in theory) for stability.

My servo arm is also quite a design challenge that I hope I have mastered.

My only problem is getting a longer and stronger servo arm screw for the titanium servo shaft, I worry the screw will shear off or strip outeasily. I will know tomarrow.

My Custom servo arm uses the aluminum servo arm that came with the servo then I encase it inside a triangular tube made from .07 x .43inch carbon strips reinforced with glass and a solid triangular foam glass rod inside . This arm needs to be incredibly stiff especialy against twisting.

I would love any comments on this good or bad, thanks!
Last edited by Tuner; Nov 15, 2005 at 04:33 PM.
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Nov 03, 2005, 03:07 PM
Coaxially Fixated
copperclad's Avatar
hi tuner
very cool machine , great post , looking forward to pictures of your build and info on your experience getting it to work , not sure what to recommend on motors but it think you might do well to try props like the slowfliers use , go with as large and as shallow a pitch as you can get your hands on , they have great pull right from startup , i would think it would fit your application well , they are great for hovering
Nov 03, 2005, 03:27 PM
Registered User
Thanks SlowFlyer Props are on my list of To Try.
I am learning about pitch and I think my 8 is a tad high think it should be around 3-4. So I will look into an APC 14x4 maybe even a 15x4?

I know GWS has some Small Heli Rotors curious if anyone has played with these or anything similar to them directly connected to an outrunner.
Nov 03, 2005, 03:43 PM
Coaxially Fixated
copperclad's Avatar
yes a 4 pitch sounds good like a 14 X 4 , with a small heli rotor you might be better off gearing down the motor , there are a mess of choices and deciding on the initial list can be pretty tuff , remember small heli rotors will need extra servos to control them , fixed pitch is two servos per rotor , and then times 4 for your setup , CP would be 3 servos per rotor , so we are at 16 channels , thinking about rotors makes the folding props look alot more doable
Nov 03, 2005, 04:09 PM
Registered User
Good..you started a new thread for this design.

There are lots of posts in the UAV section of the forums on micro computer controllers. The Gumstix project may handle your mixing/control problem.

The plan for it to walk sounds like a design consideration after all the other problems have been worked out.

Now for the design..do you need 4 batteries? I can see the need for 4 motor controllers but 4 batteries seems unneccessary. How about one 3000mah.

Where on the airframe do you plan to fasten the batteries?

Nov 03, 2005, 04:56 PM
Registered User
As of now it is easier for the 4 batteries. I want to eventualy include the ability to connect all batteries together and have the ability to switch between 4p & 2s2p This will be nice for added power when launching VTOL style from the ground. These four motors will gobble up a 3000mah battery in only a couple minutes. Also the size of 4000mah-6000mah pack does not work for me and 4 2100mah packs are perfect in size, when lined up the long way, to fit in the fuse.

If I used Heli Blades it will be a fixed pitch system or a variable pitch at most but their would be no For/Aft Left/Right control. The more I look into Heli blades the worse it sounds as they seem inefficient.

As fare as battery placement, glad you asked.
I considered mounting the batteries in the wings so all I have is one servo wire going from wing-to-fuse(at pivot wing point), along with less load on the wing pivot points(servos).
I figured to save some weight I will use my batteries as the main structural support for the now very light and thin fueselage. The fuse is about 1" thick and 5-8" tall it acts as the Rudder(along with wintips). This may cause problems hovering in wind but the wings will cause similar problems so I gave up and focused on forward flight stability.

I will have to check out the PIC mixers. I have looked into all the GPS/AutoPilot systems. I thought I might have to build my own PIC Controller setup(I hate to build from scratch).
Shouldn't a High-End Computer Radio have near unlimited mixing abilities. Or are they limited by the Mixing Modes Heli Glide Airplane. I thought at least this new Futaba could do the job or be programmed by me to do so.
Nov 03, 2005, 08:22 PM
This stuff is so cool !
joe@tech-mp's Avatar
Even if you had a radio that could do it "all", you will still need to do some of the mixing on board the aircraft in order to use gyros and/or FS systems.

Nov 03, 2005, 08:45 PM
Designer of Flying Things
-=SLaPPiE=-'s Avatar
I was able to get my JR 8103 to play right on a 4 blade setup, but in a symetrical "t" configuration where yours is "x", or "i". I also got gyro stabilization without any mixing board. https://www.rcgroups.com/forums/showthread.php?t=414145

I thought about something like that but just moving the blades.

I think you ought to have a carbon tube running from motor to motor, and swing the wings/motor on bearings. Then the servos don't see all that load. I did learn with my project that everything needs to be pretty stiff, or you get wierd vibes close to the ground.

Your project looks real cool, and inovative. It should do some cool stuff.
Building season is coming!

Nov 04, 2005, 11:38 AM
Registered User
Tuner, I'm building a v22 osprey. Many problems simialar to yours. If you used a TH2 and used the output to the servos into your speed controllers I think it might solve your problem. I also worry about all that load on the servo and think a crosshaft my be a good idea if you have problems.
Nov 04, 2005, 02:30 PM
Registered User
Yah I am impatient so I am using existing kits and doing as little custom fabrications.

I have glassed the wings and added a carbon spar. I have figured that everything needs to be stiff so that was my number one focus. I am hoping that even if their is flex the foam will help dampen any wobbling. I am 100% focused on stiffness. I am hoping the wings and fueselage will help focus the prop wash when in hover mode to minimise ground effect issues.
The motor wing fuselage strucutre seems flimsy in its shape as it is in a upsidedown c formation instead of a nice triagle like we would want. Extra care has been made to reinforce this. Each wing weighs 100g and is 24" long. The servo horn is stiffer than a wedding prick on all axis.

As fare as the servo handling the load. I had considered not doing this. But I did not want to machine a gear to fit on my servo. If anyone wants to help me with this I will change this immediately as this is the the only comprimise I have made that I did not like. So I used the best dam servo I could find and hope for the best. Surprisingly I have done some stress test with a mochup I have and it handles the load very well but the actual peak stresses could be 2-3 times what I tested at.

Eventualy I will have a custom wing designed and maybe ducted fans. This is a 100% demonstrator only and I dont even expect it to fly just illustrate the concept and pin down design holes & characteristics. But I will do flight tests from a tether and the back of a pickup unless all looks good I may never fly it untethered.

I had even considered designing my own very wide diam. 24 stator outrunner motor to swing heli blades ungeared and I wanted to integrate variable pitch control into the motor case design. I think a motor like this could change electric helis

I will have some photos tonite of one wing assembly maybe 2 and the whale basic airframe by sunday. Im doing a thrust test of the Cemech Marothon 200HT we will see how close hobby-lobby is in their stats.
Last edited by Tuner; Nov 04, 2005 at 02:40 PM.
Nov 04, 2005, 02:54 PM
Registered User
Rich it is nice to see a 3 rotor system working. I originaly designed this with 3 wings and 3 motors, like a long-ez but a motor up front and 1 on each wing, but I could not rotate the single motor to offset for torque. Then I saw some advantages to 4 wings 4 motors and went for it.

I love your model it should be a kit or plans IMHO.
Last edited by Tuner; Nov 04, 2005 at 03:04 PM.
Nov 04, 2005, 03:03 PM
Registered User
I know it sounds silly but I am hoping to lean enough about 4 rotor systems to find a novel way to stabilize it without gyros and thermal horizon sensing as this adds way to much weight. Plus this flys like a plane so it is only in hover mode for take-off and landing. I found a great article http://www.araa.asn.au/acra/acra2004/papers/pounds.pdf

This is why I am using folding props as the offset pivot points act as a dampended rotor head like what they use in this article (In my logic at least). The offset from the center of the pivot points acts as the spring they use dampen movement(In theory).
Nov 04, 2005, 03:08 PM
dusty bible = dirty life
Majortomski's Avatar
Are there counter rotating props? If not how are you going to correct for torque in the hover?
Nov 04, 2005, 06:29 PM
Coaxially Fixated
copperclad's Avatar
I think you ought to have a carbon tube running from motor to motor, and swing the wings/motor on bearings. Then the servos don't see all that load. I did learn with my project that everything needs to be pretty stiff, or you get wierd vibes close to the ground.
i think slappie has a good idea here , i wonder if the servos output shaft can handle the leverage imparted by the wing
Nov 05, 2005, 09:34 AM
Designer of Flying Things
-=SLaPPiE=-'s Avatar
The servo output arms will likely not take it.

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