Quadrocopter project

This is a discussion on Quadrocopter project within the General Discussions forums, part of the Community Boards category; same with god mode, right?...

  1. #16
    That weird Java guy xniinja's Avatar
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    same with god mode, right?

  2. #17
    Registered User kryptkat's Avatar
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    how do you control the yaw ?

    all i can imagine it doing is going spinning out of control. you have four engines all turning in the same direction you are bound to have some serious torque issues. in the same manner the tail feathers spinning on a helicopter to counter act the main rotors torque. spinning and spinning and spinning then pounce on them "ouch!" those toy helicopter rotors sure can hurt <do not ask>.

    i get how the quadhelicopter pitches forward and back and rolls left and right but not yaws left and right.

    suggestions. static dihedral or static engine offset. have few more but those should do.

    why four engines ? less weight with three and less power consumption. weight against the thrust lift of four ?



    should it go spinning out of control what is the programming function that you will call ?

    Code:
        bendover( &kiss , " tail feathers good bye!" );
    meowie ?

  3. #18
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    2 rotors spin one way, 2 spin the other.
    Quadrotor - Wikipedia, the free encyclopedia

    There is independent control of pitch, roll, yaw.

    3 propellers requires variable pitch hence mechanical linkage (if I remember correctly), and actually consumes MORE power. Props have to spin faster to generate the same lift, and brushless motors are more efficient when they are slow. Quad is also more stable.

  4. #19
    That weird Java guy xniinja's Avatar
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    And are you going to put this on youtube when you are done so we can see it.

  5. #20
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    For sure if I ever get there. It's a very challenging project right at the limit of my ability... so I'm not all THAT confident.

    It will probably take at least another month or 2, though.

  6. #21
    Unregistered User Yarin's Avatar
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    You should be using 8 props, that would be cool. (and probably more stable)
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
    A year spent in artificial intelligence is enough to make one believe in God. -- Alan J. Perlis

  7. #22
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    Yeap, you can just keep adding more and more props .

    The algorithm gets more difficult with more than 4, though, because with 4 you have independent control over all axises already. With more than 4 it becomes over-defined (or whatever the right term is).

  8. #23
    Unregistered User Yarin's Avatar
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    True, but I don't think 8 would be much harder at all.
    Still only read those 2 axis. With 4 'primary' fans on the axis, and the other 4 'secondary' fans on the corners. Because all the secondary fans would be equidistant from it's neighboring axis, simply make each primary fan's manipulation take exactly half the effect on it's neighboring secondary fans. Basically, each secondary fan would be operating at the average speed of it's neighboring primary fans. Oh, and to do it this way, you would need all the fans in a circle, not square-like, naturally.
    Pretty simple, really.
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
    A year spent in artificial intelligence is enough to make one believe in God. -- Alan J. Perlis

  9. #24
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    Neighbouring props spin in opposite direction. Average would be close to 0 .

    If we just make it spin one direction it will ruin yaw balance (it will start spinning). It's not that simple. There are 3 axises of rotation to think about, and all props have effect on all 3 axises.

  10. #25
    Unregistered User Yarin's Avatar
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    Okay lets say we're looking from the back side of the craft.
    A gust of wind tilts it to the right. So your auto stabilizer system responds by speeding up the right prop to 1500 rpm, and your left prop down to 500 rpm, while the front and back maintain the hovering speed of 1000 rpm. The 4 props I've talked about all spin clockwise. Now, the front-right and back-right props would respond by spinning at the 1250 rpm, and the left-front and left-back props would respond to 750 rpm, these 4 would be spinning counter-clockwise.
    This way the non-absolute average of all 8 props comes to 0 rpm, like you want.
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
    A year spent in artificial intelligence is enough to make one believe in God. -- Alan J. Perlis

  11. #26
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    That might work. Now you just need to convince me it's better than 4

  12. #27
    Unregistered User Yarin's Avatar
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    8 is always way cooler than 4 (look at spiders) - and cooler is better.
    In (more) seriousness: By having more props, your system is more fault tolerant, so if one of the props, for example, malfunctions, then your less likely to wreck. You could also carry more weight, and because of it's mass increase, it'd be less sensitive to atmospheric disturbances. Heavier means more room for faster computer equipment, and longer range radio equipment. If you don't want to take advantage of that extra room for weight, then you got yourself, an even more stable craft.
    Considering, I think the added coolness and stability would be worth it.
    A class that doesn't overload all operators just isn't finished yet. -- SmugCeePlusPlusWeenie
    A year spent in artificial intelligence is enough to make one believe in God. -- Alan J. Perlis

  13. #28
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    Fault tolerance is the biggest advantage I believe, but is achievable with just 6 (any 1 motor can fail without losing control of any axis). 5 also gives some tolerance (if 1 motor fails, you lose yaw control, but still have pitch and roll, so you can hold altitude and do a controlled landing). But of course, that would also require weird algorithms.

    As for weight... I'm actually trying to go the other way (make it lighter). My current design would weigh ~700g already. That should be enough for stability. I don't think stability (in terms of against wind) is as important for choppers as it is for airplanes, because planes have large areas for wind to push on (by design), and choppers don't. Any more weight would just eat battery life, and require bigger motors/props. Less weight also allows faster acceleration, which actually means better stability (the motors can react to changes faster).

    I don't need any faster computing eqeuipment. I have a 600MHz ARM onboard already. That's way faster than what I need (stream video). The control algorithm will be limited by the relatively low update rate of the IMU (sensor that gives orientation information).

  14. #29
    Registered User kryptkat's Avatar
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    that would have been one of the several other suggestions. i could not work out how it would work. i could only foresee it getting stuck in a correction control loop. ie pitch forward a few degrees and it would have to correct for yaw. correct for the yaw and it would roll. then it would have to correct for the roll. while doing so it would offset the pitch. and so on.... i almost went catatonic trying to work it out.

    less weight would be less stable in gusty wind.

  15. #30
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    Nope. INDEPENDENT control means you can change any one without affecting others.

    I suggest Google if you want to learn more about it.

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