# Defying gravity



## mklotz (Mar 20, 2009)

Here's something you can make in your shop to confound all those people who think anti-gravity and perpetual motion are possible if we just can get the engineering right.

[ame]http://www.youtube.com/watch?v=BG8NgF8zMvA[/ame]

It's called a double cone ascender and is a popular lab demonstration in physics courses since it cries out for a nice Lagrangian analysis.

As you can see from the video, making one is dead simple. Turn the double cone on the lathe, making an effort to get the axes of the two cones coincident. My 3jaw is pretty good so I used it to turn the cones. If yours is suspect, a collet chuck may be something to consider.

The rails are just rectangular sticks of metal. They're not critical. Use anything to hand, e.g., angle iron. The only real requirement is that they are high enough so the cone center is above the table when the cone is at the end where the rails are connected.

There's a design equation that connects the various angles involved.

tan(I) < tan(C/2)*tan(D/2)

where:

I = inclination angle of ramp
C = total included angle of cone tip
D = angle between the two rails

I used C = 45 deg. With 9 in long rails, a 1/2 in riser provides just about the maximum angle for I. (I didn't bother to measure D but, by eyeball, it's about 15 deg.)


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## Tool Post (Mar 20, 2009)

I like it a good "simple" project, we need more like this.


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## speakerme (Mar 26, 2009)

Sadly the video seems to be no longer available!

Chuck m


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## mklotz (Mar 27, 2009)

I just clicked on the video and it's working for me. I haven't moved it or renamed it or ... so I think the problem may be at your end.


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## R.Johnson (Apr 7, 2009)

What's the dimension of the double cone?


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## mklotz (Apr 7, 2009)

The dimension of the cone is not critical. Mine is made from 1" rod with an approximately 5/16" cylindrical section left in the middle to facilitate gripping in a collet while the second conical surface is turned. Thus the OAL of the piece is about 2.625".

Recently, I wrote up a derivation of the design equation for my own records so I'm attaching that to this post for the edification of any physics students reading this.


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