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Variable Pitch Quad Rotor - M/UAV

Posted by fibrewire on March 14, 2010 at 12:30pm

Variable Pitch Quad Rotor - M/UAV

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DIY project ranging from a 600cc 120HP etec Ski-Doo engine, UltraSport 254 tail rotors, extruded aluminum blades from Vortech, aluminum / steel tube structural components, and a carbon fiber reinforced polymer monocoque frame.

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  • Moderator
    Roberto Navoni April 1, 2010 at 6:53am
    Hi Robert,
    In our project Multipilot Board we had develop HG3 a Variable Pitch Quad ... see my repository ... http://code.google.com/p/lnmultipilot10/ and the video of HG3
    Regards
    Roberto
  • fibrewire March 16, 2010 at 5:53pm
    I was hoping to put temperature and vibration sensors on each gear drive and rotor housing - then anything outside normal operation would send a yellow alarm to return to base, red alarm would disengage the engine and perform an emergency landing. There would be a relatively generous window between detecting excess heat and vibration and actual bearing seisure.

    Sometimes in actual helicopters, a loud bang is heard coming from the main transmission and loss of power occurs with warning alarms going off, and then right before ditching the rotorcraft, all the power comes back and noise goes away. Upon inspection after the incident, several teeth from main gears are chipped, and the transmission gets overhauled. Other times the pilot and passengers aren't so lucky.

    I like that variable pitch motor! The rotor gear boxes I have operate on the same principal, but there is a collective bearing block that attaches to the center shaft to pull the pitch actuator up and down. Any ideas?
  • Vicente March 16, 2010 at 3:32pm
    Hi Robert,
    Nice project!
    What are you going to use as clutch or one way bearing between the rotor and each drive chain?
    Without that, after engine or bevel gear failure would be impossible to perform an autorotation.

    Probably a good idea is to make a small version of you model using this type of motors, maintaining constant RPM and changing just the pitch. Well at least cheaper way to tune you code and test the electronics.

    Good luck...
  • fibrewire March 16, 2010 at 1:12pm
    Maybe i could use a small tank of compressed air attached to the drive shaft that will trigger on close proximity to the ground, providing enough blade momentum at that crucial moment.
  • bGatti March 16, 2010 at 8:26am
    Every time the idea of a larger quad comes up - it is met with the same 2 issues: - 1. quad is only lower complexity because it is electric, and fixed pitch, and 2, the failure modes are not very good for quads - which is fine for cheap and light, and less fine for expensive, heavy, or human occupied. But I will give you that many a flying car motif is based on multiple rotors (often ducted fans). Here again, the failure modes are a bit thin.

    Autorotation depends on a few factors, chiefly the ability to convert downward movement into blade momentum, and then finally to use blade momentum to flair the landing. This is increasingly challenging as blade size gets smaller (and less efficient), but not impossible.

    The big benefit over a heli would be the ability to fold the prop bars in, and store the thing in a garage - making suburban heli-commutes practical in theory for the first time (or something like that).

    Also I think a variable pitch prop is still far less complex than a full on flybar.

    Good luck...
  • fibrewire March 15, 2010 at 7:45pm
    Sorry, i was pretty tired and never meant to justify my reasons for my project - sometimes i feel the need to explain things when people give me a "can't happen, won't do it" attitude. I'm not snapping at you, just taking preventative measures for "bandwagon belittlement syndrome." Then again, i'm brand new here and i don't know how people reading this forum will react. I am used to a pretty competitive cutthroat environment, and i apologize for being quick on the defense. I do appreciate all input on how to suceed with a quad rotor system!

    Torque is balanced by connecting the rotors to a capital H drivetrain. Rotors on the left side of the "H" will rotate clockwise, right of "H" will rotate counterclockwise. Main drive will occur at center of "H" drivetrain. At four blades per rotor and all rotors being mechanically linked, it will be interesting to find out what the minimum height to perform an autorotation will be. I'm sure that because of the size of the blades that autorotation will have to occur within a few feet of the ground. Luckily after making some calculations based on multiprop aircraft such as chinooks and osprey compared to other similarly sized helicopters, i can just tell the computer what to do in case of an emergency.
  • Xander March 15, 2010 at 12:09pm
    Ok, I should take a step back. Of course you don't have to justify your project here. Having fun and or making it a learning experience is reason enough regardless of the merits of the machine.

    And you're right that a fixed pitch quad likely wouldn't work on the large scale. The only reason using speed control works well on the small scale is that it has very little momentum. But, if we're looking at this from a practical point of view, that doesn't explain the need for a full sized, variable pitch, quadrotor. Your argument seems to be that a quadrotor is more forgiving (of component failures?) and easier to use, but I don't really see how you get there. A normal heli can loose power entirely and autogyro down to the ground safely. Doubt you could do the same with a quad. The computer really has to be in complete control in order to maintain stability. Maybe you could loose a rotor and manage to compensate, but that's easier said than done when the only thing stopping you from spinning out of control is the balanced torque of the motors.

    Which also brings up the question of how you plan to balance the torque. I assume all of your tail rotors are designed to spin the same direction. A quad with all the props spinning the same way is no better off than a heli without a tail rotor. Most quads have counter-rotating props to cancel eachother out. Tilting one or more props could do the trick, but that's yet another added complexity.

    Honestly, I'd love to see an application for quads on the large scale. They're cool looking and a refreshingly different take on flying. But once you step away from the fixed pitch idea I just don't see the justification for it. This isnt a car. More rotors don't make it automatically more stable. I just don't see any benefits it has over a conventional heli, and it certainly comes with some disadvantages.
  • fibrewire March 15, 2010 at 5:42am
    Also, ask any helicopter pilot if they would like to be revving an engine up and down all day as opposed to varying pitch. Autogyros are a proven technology, and even the coaxial micro rc helicopters have a collective. Take a second and look up "Alien Jump Jet" in youtube, and see that it has 1.5 million views in two years with no media coverage, and the Moller SkyCar has 2.5 million views over 4 years and every kind of media coverage across the planet. The SkyCar sucks, yet a toy is popular. Why? Because it's learning curve is low, it looks simple, and there is nothing to figure out. Need more proof? Look up "orbitwheel" in youtube and pay attention to the feeling you get when you see this.
  • fibrewire March 15, 2010 at 5:27am
    Ok, lets look at this from a practcal point of view. Tons of things in our life are consistently made easier and simpler, but why? Because the lower the learning curve, the more likely it is to be adopted. Take this computer. I've been using computers since Commodore VIC 20 and the Atari 400. If i showed most people what it would take just to boot the machine, they would laugh and walk away. But turn on Windows 7 and anyone can stumble around and figure out what they want it to do, because the learning curve has been decreased. Would people want to drive a car if it had a cyclic and rudder pedals? The reason is because the quad copter is engineered to be forgiving, regardless of it's complexity. Take a car, it has four tires that are constantly in connection with the road. 4 times the chance of failure. But anyone can jump in a car and figure out how to drive it, because it's a forgiving system. I'm not saying that this quad rotor will be perfect, but this is where I think technology is going.
  • Xander March 15, 2010 at 12:59am
    From everything I've seen, the main benefit of a quadrotor is that it is mechanically simple. By going variable pitch you pretty much do away with that. You end up with all the mechanical complexity of a normal helicopter (even worse really, with 4 rotors) along with the inherent instability of a quadrotor (lacks the gyro effect of one big main rotor).

    It'd look cool, yes, but does the machine you propose offer any advantages over a helicopter? Perhaps it'd be more agile, but is there even a need for that?
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