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  • Middle school project - motor that goes up and down (slowly)?

    Discussion in 'The main mechanical design forum' started by Rose, Feb 18, 2015.

    1. Rose

      Rose New Member

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      Hi, so I'm asking for my sister who is a middle school student. Her project is to create something like a merry go around model. The horse of the model would need to go up and down (vertical motion), so we will need to have a motor for that. What is the cheapest one you'd recommend? The whole model is around 30cm in diameter with six horses (say like with the size of around 10cm height and width) that move up and down on it. Thank you for any input.
       
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    3. K.I.S.S.

      K.I.S.S. Well-Known Member

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      Hi Rose,
      The thing with motors is that most of them (especially small ones, like you'll need) are designed to rotate quickly. There are electronic ways to slow them down, but for DC motors, which is what you'll need, this results in a loss of power.
      So the best thing to do is to fit a gearbox to the motor - this will slow down the speed but increase the power - if there is a brother, get hold of one of his old remote controlled cars and take out the motor and gearbox. On some RC cars, you can change the gear settings to slow it down, but with more power..
      And you only need the one motor - make the motor drive the central shaft around and have the horses up and down movement controlled by something like a wave washer - that's a washer that has little 'up and down' bumps in it. It only needs to be small and quite close to the center of the shaft, so any small movement there will become a larger movement at a wider diameter (where the horses are).
      There's loads and loads of little D.C. motor and gearbox combinations out there, and with a gearbox, you can also use a variable resistor (like a volume control knob on a stereo) to change the speed, and it shouldn't affect things with such a small model.
      If there isn't a brother available to pinch things from, ask at a local remote control hobby shop.

      Hope this helps,

      K.I.S.S. (That's my user name, and it stands for Keep It Simple, Stupid... Not you - it's just what I remind myself of everyday)
       
    4. maniacal_engineer

      maniacal_engineer Well-Known Member

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      Like KISS said find a small motor and gear it down. However gearing to a lower speed does not increase power, it does increase torque. power is torque X RPM (X a unit correction to get units that make sense). but power is not increased by a gearbox. Sorry to get pedantic about it, but it is just as easy to get that bit right.

      for the horses you can do something very much like what a real carousel, as shown here in lego
      http://www.robertcailliau.eu/Alphabetical/L/Lego/Models/Rebuilt Carousel/
      or here
      http://flickrhivemind.net/Tags/carousel,wwwalbanybrassringcom/Interesting
      in real life

      Bevel gears may be hard to come by, so you ca use the same idea but instead of a gear at the root of the shaft have a crank that follows a cam cut as a wavy top to a cylinder. this will get the shaft to rotate back and forth and then a horse on a crank at mid shaft would go up and down.

      http://www.gutenberg.org/files/42369/42369-h/images/fig094-096.png
       
    5. Strambo

      Strambo Member

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      Doesn't this thing rotate on its axis?

      Hi,
      The whole merry-go-round rotates on its axis; right? Do you have that motor all worked out?

      I would get the rotation from a strong, hobby-shop gear motor to work, and then use a simple cam to cause the horse to go up and down as the whole thing rotates.

      The horses are mounted on a stiff wire that slides thru bushings or holes, at its top and bottom. The wire pokes thru the floor of the merry-go-round and has a tiny wheel or a very slippery cap on its end; it is that end which rides on the surface of the cam hidden underneath.

      The cam is a piece of stiff plastic sheet, flat on the bottom and cut like a sine wave on the top. It wraps around to form a circle about 25cm in diameter, and is just as tall as it needs to be to hide under the merry-go-round. Its upper edge is the series of "cam lobes", or mountains and valleys, that the horse assembly rides on to make it go up and down as the merry-go-round rotates.

      Good Luck.
       
    6. Strambo

      Strambo Member

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      Alternative up&down mechanism: eccentric wheel

      Another way to do the same thing: the horse still rides on a slim vertical shaft that slides up and down, but instead of the circular wavy cam, mount an eccentric wheel on the bottom of the horse's shaft. This wheel is grippy enough to roll as the carrousel rotates around. See this wheel:

      https://www.flickr.com/photos/17534977@N00/3444251479/

      The bicycle using this wheel would go up and down smoothly with every revolution of the wheel.

      If any of this sounds good, let me know and I'll post a sketch :)
       

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