If at first Quad didn't succeed, TRI TRI again

3689386384?profile=originalFollowing the death of the Ugly Pink Quad's 4th thruster, Entirely accidentally, I am going for a tri-rotor design, on 

a 1/4" plexiglas base, with 3 Futaba S3003 servos for vectoring thrust.

The Nano that was originally being used for the Ugly Pink Quad, and now the Tri, well...it died, so in comes the DFRobot RoMeo.


My initial idea is going to be to use the thrusts of the three ducted fan units to stabilize horizontally and control altitude, while using vectoring to produce the X-Y translations and yaw motions as needed.

Given the wide, flat body and the ability to vector thrust, I might be able to use the plexiglas as a lift-generating device to aid battery life when not merely hovering.

Given that lift, and position can be somewhat decoupled, it may end up a very stable platform for cameras and such, even in breezy conditions.


I hope to have the IMU stream stabilizing the platform by mid-week.

First test with the AFSoftwareSerial for COMMs with the ArduIMU seem promising.


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  • Moderator
    ...but hovering ain't it!
  • That information is what I hope to get from future testing.

    What I know to begin with however is:

    1) If you picture the pitch of the prop as tracing a spiral through the air, if a point on that spiral is moving at the same linear speed as the airframe's airspeed, the fan thrust becomes zero.  So for a given RPM there's a max airspeed where thrust drops to zero. (Ignoring airframe drag for now)

    2) As airspeed decreases, the angle of attack of the blades increases, and "lift" (aka thrust) also takes a hit.

    Therefore any bladed propulsion system will have a curve to it, a performance range that's acceptable, and a sweet spot to try for.

  • You do realize that ducted fans (or any high pitch prop) are most effective at high speeds (~100 mph), and least efficient at standstill?

    This can work, but with reduced payload * time than an open prop with much lower pitch.

    Best of luck all the same.


  • you never fail to impress me!


    do you have photos of any other robots or anything you have made?  I kind of like your style :D

  • OH! And it's an ArduIMU+ V2.


  • I'll pre-second it :-)
    "I'll take a closeup of the fan to servo mounting tonight as comedy relief for the forum :-) If it works as-is, I'll be making something MUCH more robust soon."
    Also, the decision to go ducted fan has caused much discussion and second-hand "I read that some guy said that (insert variable here) isn't as good", so I'll do some research to get some concrete numbers, thrust-curve comparisions, and real-world trials between equivalent-thrust open-props vs ducted fans, with respect to quad/tri/birotor/single prop VTOL setups.
    Should make for a very interesting and noisy weekend soon ;-)
  • Moderator
    I will second Sebastians comment, those servos won't last long like that.
  • you want to lift the copter on the servo horns?

    i would try to get it more robust there


    which IMU are you using? looks like an ArduIMU on the image

  • I may have to do some mixing with the vectoring and throttle, but at the moment it hasn't been in-air yet.

    I designed in a little camber to the mounts, which I hope will act similar to a wing's dihedral.  If it does, then stabilization should require very little change in fan speeds, leaving fan speed entirely linked to elevation.

    I'll take a closeup of the fan to servo mounting tonight as comedy relief for the forum :-)   If it works as-is, I'll be making something MUCH more robust soon.

  • Moderator
    Something to note about ducted fans.. is generally they take have a slower response to throttle.  Its something i have heard on RCG forums but I have personally never verified this.  But still its a cool idea to use ducted fans :)  hope you can get it working!
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