Today everybody and their dog seem to be working on a quad project. And with my own quad having reached a relatively mature stage with stable flight some time ago, I thought it would be nice to try something different.

So inspired by the full-size Osprey tilt rotor design I just started an experimental duo/tilt copter build. Frankly I am far from sure if it will ever fly, but that is what makes it fun!


Mechanical:

My tilt design is one I used in an earlier tri-copter build. I insert a 8mm CF rods into a 750x10,5mm CF square tube and glued then together. A modified T-Rex 600 blade-holder is then inserted on the 8mm tube and fastened using glue. Finally a servo is epoxied at the side of the square tube and linked to the 600 blade-holder. Motor and ESC is a cheap TowerPro combo from HobbyKing. Cheap and easy to replace when experimenting, and the ESC has no problem handling 333mhz PWM pulses.


Hardware / software:
For control and stabilization I will use the same hardware that I used in a Quad I built earlier. A FASST R617FS receiver modified with PPM output, and the ArduIMU V2 board with custom software for stabilization and servo/ESC control.

Main body / tail:

I have yet to decide what I will do for a main body. At the very least I will need some kind of tail with a lift surface to get some balancing momentum in the pitch axis, and tail drag when in forward flight. Lots of fun experimenting to be done!

Parts:
Carbon Fiber Square Tube 750x10.5mm
Carbon Fiber Tube (hollow) 8x750mm
Align T-Rex 600 Blade holders and bearings
Turnigy S3101S Servo 17g / 2.5kg / .14sec
TowerPro BM2410-9T / 18A BEC/ 1047 Prop Combo
Futaba FASST R117FS receiver
ArduIMU+ V2 (Flat)

Views: 3849


Developer
Comment by John Arne Birkeland on July 31, 2010 at 11:02pm
When I used the ArduIMU together with GPS in a airplane I had problems with the pitch being affected by acceleration and deceleration. Also if I turned the plane against the wind hanging on it so that ground speed approached zero, the IMU would sometimes go into a oscillating feedback loop. I do not see the need for a tail gyro since I already have that gyro axis in the ArduIMU. My initial setup will most likely be a body with a fixed T tail. The elevator surface will be angeled so that forward motion will pitch up the nose to combat the forward tilted motors pulling the nose down.
Comment by Mike on August 1, 2010 at 4:17am
Sounds like a Gress bicopter?

Developer
Comment by John Arne Birkeland on August 1, 2010 at 8:05am
@Mike: Yes, that is pretty much how I will build it as a test platform for hovering and initial transition into forward flight. But eventually I plan to add wings so that I can convert fully into horizontal flight. If you squint you can see the Gress bicopter as a Osprey V-22 without wings.
Comment by Darren on August 1, 2010 at 8:45am
I was thinking of starting a Modified Quad along these lines as well, but using two of these on the tilt setup.

Was thinking of going for something along one of these... Which may give you some ideas on the tail.

Comment by Darren on August 1, 2010 at 8:51am
Sorry the graphic didnt come through, here is a pic of the Samson.

Comment by Roy Brewer on August 1, 2010 at 12:58pm
Sounds like a neat project.

As mmormota points out, I suspect you may have longitudinal control issues in hover (if you consider your craft to be oriented like a V-22). Symmetric rotor speed gives you thrust control, differential RPM gives "roll", differential motor tilt gives yaw control, but how do you generate "pitching" moment without cyclic blade pitch control or a separate (lifting) tail rotor?

Unlike a quad, you may also have to deal with inter-axis coupling (which could improve if you use the couter-rotating rotors, as Darren (and james Cameron) suggest

- Roy

Developer
Comment by John Arne Birkeland on August 1, 2010 at 1:51pm
In theory... and also hopefully in practice you pitch by tilting both motors forward or backwards. With both motors tilted forwards the nose is pulled down and the craft starts to move forward. To make this controllable you will need some body mass along the pitch axis to act as an balancing pole, and CoG to be centered under the motors. The gyroscopic effect generated by the propellers should also help stabilize the pitch axis. But yes, I am not expecting this to be easy. The whole concept in one big balancing act. :)

Moderator
Comment by Gary Mortimer on August 2, 2010 at 1:58am
Your building a Gress

Comment by Jonathan Lussier on August 2, 2010 at 12:55pm
I think I saw a discussion on this at RCgroups, the main problem is the sheer mass that you need in the fuselage. Otherwise, when you rotate your props, the fuselage will rotate instead of the nacelles!!
Comment by Darren on August 2, 2010 at 6:07pm
main reason for bulk of the fuse, is commonly used for payload. as flying sticks are common :) but I do agree it can and does assist in the balancing act of transition to foward flight.

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