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I want to build a mini-hoverboard (2" by 8" scale model)

  1. Jun 1, 2014 #1
    For the past week or so, me and a buddie have been trying to figure out how to make a mini-hoverboard kind of this, now it doesn't even have to look like a hoverboard we just want it to be able to get off the ground with 2 fans.

    What we were going to order was all this stuff
    https://docs.google.com/document/d/1AAHYts99fkmgoLAE8p_428diVQrDkwB1hzbqKf9NKAk/

    Our design was to be 8x2 and up intill today we thought 2 2''*2'' fans would cover it, and we now realise they won't, and we have been looking up things for hours trying to find out how to calculate the thrust needed to lift it up, and find an estimate of the weight so we could do that, or even find fans capable of lifting themselfs up, and so far nothing, so how can I make this work?
    q1tsMGs.png
     
    Last edited: Jun 1, 2014
  2. jcsd
  3. Jun 1, 2014 #2
    You might consider looking at quadcopter parts.

    But, there are a few other problems that you'll run into. The device will have to carry its own power source, and batteries are relatively heavy. Power sources that contain a lot of energy per unit mass, like lithium-polymer batteries, pose a serious safety hazard without special protection circuitry. A watch battery can't power a fan capable of lifting itself.

    More importantly, if the board lifts off the ground, it will spin uncontrollably until it flips itself over and propels itself to the ground (probably within the first second). If you read up on quadcopters (or even regular helicopters, which have blades on two perpendicular planes to control spinning), you might find ways to handle this. I don't have the expertise to suggest anything specific.
     
  4. Jun 2, 2014 #3
    On one hand I don't want to discourage you from trying but I think it is important to recognize how stacked the odds are against you to avoid wasted expenses or personal injury.

    Large numbers of humans have always been jealous of birds. To be able to turn our world mobility into a real 3D experience that is as close to portable and (seemingly) effortless as birds is incredibly seductive, but we just aren't built like birds. It is largely a problem of scale. At our size and mass density devices that can even create a basic hover, let alone swoop around, require significant amounts of power. So far the only thing even approaching a "personal flier" has been so-called jetpacks and these can only last for a very few minutes since even adding the weight of enough fuel to last longer makes them untenable. Please note that many great minds with fairly vast resources of money have failed for well over 100 years to overcome the limitations.

    It's not that some advances haven't been made. Consider that even scaled down as in model aircraft, only 20 years ago the only power that could create flight was jet, rocket, or internal combustion and now there are electric models that fly rather nicely. However they are very light and quite small.

    To keep your expenses down and avoid personal injury I suggest you work with models first, like the Wright Brothers did. Perhaps take a working commercial model and try to make it 3-4 times the size. I think you will be amazed at how difficult that is. Then imagine making it 8-10 times that size and you will begin to see the limitations.... basically impossible with present battery technology. Then consider that even at 10 times the size, if we keep to scale (and we can't... it gets more demanding as it gets bigger) at most it might weigh a kilogram. Then consider how big and how powerful it would have to be to lift 50 kg. See? Rather daunting.
     
  5. Jun 2, 2014 #4

    Nugatory

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    Staff: Mentor

    It looks as if they're planning on a two inch by eight inch hoverboard, not two feet by eight feet... So not so unrealistic. Nick O's suggestion about quadcopter parts looks like a good starting point; and also look at what the RC aircraft modelers are doing. Stability might be the hardest problem to solve.
     
  6. Jun 2, 2014 #5
    One more comment: quadcopter blades can be dangerous! Try not to leave them exposed where they can hit your fingers (or head!) if it goes out of control.
     
  7. Jun 2, 2014 #6
    Yes you got the 2 inch by 8 inch part right, I don't think its a good idea to try to do something of that scale (Yet), and I wasn't quite functoining so let me clear some stuff up, my main issue is that I can't find a fan capable of producing enough lift, I've looked into model airplane engines but there all almost too big and to pricey ($50 for JUST the fan, not even with the engine?) so what I'm trying to find is a small 2-5 inch fan capable of lifting itself and a few ounces of weight.
     
  8. Jun 2, 2014 #7
    Update:
    v3
    Xwc3NUZ.png
     
    Last edited: Jun 2, 2014
  9. Jun 2, 2014 #8

    davenn

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    I still think you are going to struggle
    with the weight of the fans, board and batteries ... its going to be more significantly more than "just a few ounces"

    and as soon as you find fans strong and small enough, you will have to use modelling motors and they WILL cost you serious money, to lift it all, it WILL flip over.


    That is why they use 4 fans - Quad copter or even the 6 fan hex copter
    its all about lift stability, with 2 fans, that isn't going to happen

    My mate who is into quad copters in a big way has told me in the past, that even trying 3 fans at tips of a triangular platform isn't stable enough

    cheers
    Dave
     
    Last edited: Jun 2, 2014
  10. Jun 3, 2014 #9
    Ooops. I did overlook the dimensions, getting hung up on "hoverboard" and envisioning Back to the Future sizes. Now that I'm seeing this is in model sizes I'm quite intrigued, though I suspect still it could get expensive.

    There are several studies going on for extremely small flying bots that act in swarms, thus requiring some onboard computational power as well as inter-communication. Apparently some strong advances have been made in this area so that possibly soon, making a tri-fan or simply providing a higher margin of stability for 4 or 6, may be available (especially since yours might not need the radio communication at the start), though I doubt "on the cheap". That said, if it can save you on one or more fans that might be a net gain. This could get fun!
     
  11. Jun 3, 2014 #10

    rcgldr

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    Tri rotors work just fine, mostly due to the electronic gyros that almost all multi-rotor models use. Most of these use arms that extend from a central base as opposed to a triangular frame. There are also 6 rotor models that use just 3 arms, with one rotor above and the other below the end of each arm.

    Double and single rotor models are basically helicopters, and the rotors have variable pitch, with at least cyclic control input to control pitch and roll axis, and commonly collective pitch, where the overall pitch can be adjusted as well.
     
  12. Jun 3, 2014 #11

    AlephZero

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    How do you balance the torque, with an odd number of rotors? Do you need a helicopter-like tail rotor as well?

    An even number of rotors with half of them contra-rotating sounds like a better concept.
     
  13. Jun 3, 2014 #12
    Update:
    v4
    GyMnS5y.png
     
    Last edited: Jun 3, 2014
  14. Jun 3, 2014 #13

    rcgldr

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    The center of mass is offset and/or one arm is longer than the other two. Example video below. At the start of the video when the tri-rotor is on the ground, the "front" is the arm pointing to the left, and the center of mass is offset towards the "back" which is to the right. In the video, the model has been set to aerobatic mode, and the pilot ends up "landing" the model inverted. There's more example footage after the "landing".

    https://www.youtube.com/watch?v=mOnvISm2_KE

    This one is being flown in a more stable mode:

    https://www.youtube.com/watch?v=ss9dqokDYu4
     
    Last edited: Jun 3, 2014
  15. Jun 3, 2014 #14
    Alright- so far you guys have helped alot, buuuuuut I still can't find a good fan that can lift around 2 ounces (~60g) and is under $30 each. I could calculate this myself, but I'm not quite sure how I could calculate the lift and thrust and all that, so even if you can't find any fans, can you just through the formulas out there?
     
  16. Jun 3, 2014 #15

    sophiecentaur

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    A hover vehicle needs much less power than a helicopter. It is very much in 'ground effect'. I would suggest that you look into the many r/c mini-helicopters that are on sale and think about using the battery and fans from three of those. Actually, you may only need one, if you are prepared to use a 'skirt', as in a normal hovercraft. The bigger the area of the board, the more stable it should be.

    If you want an idea of possible performance, it may be best to just get hold of one of those helicopters and measure the force available. You could tether it to a see-saw style balance, to make it well behaved.
     
  17. Jun 3, 2014 #16
    Thanks for the response, I will be trying to see if I can grab a couple of helicopters in the next few days.
     
  18. Jun 3, 2014 #17

    rcgldr

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    You can buy a small quad rotor with transmitter, battery, charger, ... for less than $50 (USA), probably less than trying to buy parts and build something from scratch. You might be able to find a small 2 rotor tandem (not on a shared axis) helicopter also.
     
  19. Jun 3, 2014 #18
    I don't plan on building a quadrotor, or buying something pre-built, I want to do something myself.
     
  20. Jun 3, 2014 #19

    Nugatory

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    Staff: Mentor

    There is the possibility that you can buy something prebuilt and spend some time tearing it apart... and end up with a collection of parts that will work well together for less than the cost of sourcing the parts individually.
     
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