How to increase thrust of battery-powered hovercraft

Discussion in 'The Projects Forum' started by tjohnson, Jun 24, 2015.

  1. tjohnson

    Thread Starter Active Member

    Dec 23, 2014
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    For a few years I've had a hobby of building small hovercraft, which is one of the primary things that got me interested in electronics. After making a simple one several months ago, I've been wanting to make an improved one that can hold the weight of a 9V battery using propellers instead of fans.

    So far I've made two test models:
    Hovercraft B 003.JPG Hovercraft B 004.JPG Hovercraft B 001.JPG Hovercraft B 002.JPG
    which both scoot across the floor if I give them a push, but don't zoom across the floor spontaneously the way I would like.

    The second model uses a lot of power (I think it ate a fresh 9V battery in 20 minutes), and I know that a rechargeable lithium 9V battery would be a more lightweight and (in the long term) affordable power source, so I hope to buy one soon.

    I would appreciate any ideas for how I could increase the thrust.
     
    Last edited: Jun 24, 2015
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    It looks like the bottom of your "body" is completely open, full area of the body. Don't know how they're doing these now, but in the olden days, they only had a small opening around the perimeter of the body. And a 'skirt' between the body and ground/surface.

    This small gap caused the air to be pressurized and gave more lift to the craft. Many of the small ones only had one fan, used for the lift and direction was done by bleeding of air for the motivation. I think it's the lack of lift that is your problem.

    https://www.google.com/search?q=how+hovercraft+work&ie=utf-8&oe=utf-8
     
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  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    You need a fan that can actually compress air and blows more air forward than will escape past the blades. That means you either need blades that cover a large area or you need a propeller with a very steep pitch (and this is still unlikely to work). Your best bet is to get a plastic "squirrel cage" blower. The chassis must fit very close to the squirrel cage to minimize blow-back. Also, adding a duct (cylinder) to the intake of the propeller will help.
     
  4. DNA Robotics

    Member

    Jun 13, 2014
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    Boat propellers lose a lot of their power radially. I assume it works the same way for air pressure. You might try surrounding the propellers like this.

    [​IMG]
     
  5. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    And consider using rechargeable Lithium Polymer batteries designed for model aircraft, there are plenty on ebay; a 9V PP3 is not suitable for this type of application as it is too heavy and cannot deliver sufficient power to the motors.
     
    Last edited: Jun 25, 2015
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  6. tjohnson

    Thread Starter Active Member

    Dec 23, 2014
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    Thanks for the suggestions.

    I should have mentioned in my original post that I built my first model from this Instructable. I followed the instructions exactly, except I used tape everywhere instead of hot glue, which shouldn't matter. So I don't understand why it doesn't work like the one pictured there.

    @shortbus: What you said makes sense. I attached a piece of cardboard to the bottom of the foam meat tray with a small opening around the perimeter, but it didn't seem to make a difference. I think the battery is wearing down again though, so I may need to wait to do further testing until I can get a rechargeable one.

    I also checked out the link, and observed that the propellers on a real hovercraft usually seem to be oriented perpendicular to the base rather than parallel to it. I wonder if they produce more lift that way?
     
    Last edited: Jun 25, 2015
  7. shortbus

    AAC Fanatic!

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    GopherT is on the right track with a ducted fan. But don't know about a squirrel cage blower, I'd be looking at a axial fan, like in a computer. The propellers lose to much radially. And a skirt is a must, along with the bottom gap. You need to keep the air contained under the craft. And like everything in engineering scale and proportion are very important.

    http://www.popsci.com/how-build-hovercraft-styrofoam-plates

    https://www.google.com/search?q=hovercraft+plans&ie=utf-8&oe=utf-8#q=model+hovercraft+plans

    http://www.mikesenese.com/DOIT/2009/12/diy-hovercraft-plans-leafblowers-lawnmowers-4-stroke-engines/
     
  8. Papabravo

    Expert

    Feb 24, 2006
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    Thrust from a propeller is an extraordinarily complicated affair. Things like blade diameter, blade aspect ratio, blade pitch, tip speed, air density, humidity, and temperature all have effects. For example you might be tempted to try a large diameter blade with a high aspect ratio. As soon as the tips go supersonic the thrust drops off a cliff, so there is a limit to blade diameter for a given number of RPMs. Alternatively you might be tempted to increase the RPMs to some very high number with similar results. Every time you change something you run into another optimization problem. This is what makes engineering a challenge and a pleasure.
     
  9. tjohnson

    Thread Starter Active Member

    Dec 23, 2014
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    Well, I think I got that one to work better now, but it spins around in small circles and I'm not sure how to make it travel in a straight line.:eek:
     
  10. shortbus

    AAC Fanatic!

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    That's another reason they put a ring around the outside of the prop. And a rudder behind it for direction.
     
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  11. tjohnson

    Thread Starter Active Member

    Dec 23, 2014
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    Thanks, I really appreciate your help. I made some very similar models using fans instead of propellers before, and they seemed to work even more poorly. However, those models had the bottom completely open, so I'll have to try building an improved one.
    I'll definitely add those. I think I'll use the rim of a foam cup for the ring and a flat piece of foam for the rudder.
     
    Last edited: Jun 27, 2015
  12. tjohnson

    Thread Starter Active Member

    Dec 23, 2014
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    I tried building a fan-powered hovercraft with only a small opening around the perimeter, and it didn't seem to work any better than the ones I had made before.:( I'm not sure why.
    I hope to try this later today, but might not have time to since I'm moving this week.
     
  13. ericgibbs

    Senior Member

    Jan 29, 2010
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    Whats the surface that your craft is running over.?
    Looking at the original link, suggests a highly polished floor, which almost anything will slide along even with a slight prop push.?
     
  14. tjohnson

    Thread Starter Active Member

    Dec 23, 2014
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    Actually, I had the models sitting on my bed when I took the pictures. The surface I test them on is a linoleum tile floor, which is textured but fairly smooth, like the one shown here:
    Hovercraft A Mini 001.JPG

    EDIT: I just found out that I won't be able to use the rim of a foam cup for a ring around the propeller, because it's not quite large enough.
     
    Last edited: Jun 29, 2015
  15. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Cut a strip from another foam tray and glue it to the one with the prop. An upside down "U" shape would be fine. Just need to keep air from escaping from the prop tips.
     
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  16. tjohnson

    Thread Starter Active Member

    Dec 23, 2014
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    I guess the rear of my hovercraft should look somewhat like this (on a much smaller scale):
    [​IMG]
    so I'll try to design an air chamber and rudder for it.
     
    Last edited: Aug 6, 2015
  17. Reloadron

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    Jan 15, 2015
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  18. shortbus

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  19. tesla0157

    New Member

    Aug 6, 2015
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    you can shorten the windings in the motor this will give you more amps , to get more thrust , and go to balsa wood, and or grafite for light weight to start with. maybe this will help
     
  20. Reloadron

    Active Member

    Jan 15, 2015
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    Yeah, I read that one also. :)

    What really does worry me is the number of commercial airline pilots encountering the things. They really are pretty cool and a few grand gets a pretty nice one. Several months ago there was a fire in an industrial area of a town beside us. The evening news had some really cool pictures of the fire and firefighting. The photography was extremely sharp and clear. They gave the film credit to a guy who used a drone. The guy lived in a housing development adjacent to the fire and used his drone to record the video. I really wouldn't mind having a good one to play with, but with all my toys and gun collection I doubt Kathleen (She Who Must Be Obeyed) would go for it. :) Then too, she is in PA right now (Pittsburgh) visiting family. Come Oct or Nov she will likely go to Phoenix AZ and CA. to see some friends and a cousin. Those trips are usually 3 weeks. That would be the time to tell her I think I need a drone. :)

    Ron
     
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