Building a "Gyroscope" Swing ...

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Old 07-08-10, 06:46 AM
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Building a "Gyroscope" Swing ...

Hey everyone, I'm building a sort of swing - for people, not a model - that can spin (rock back and forth) vertically. As it's tough to explain, just look at this picture and you'll know what I mean:





(click to enlarge)

See there is a gondola for one person and several joints allowing it to spin in various directions. The one that's most challenging, of course, is the vertical one. I have done a complete 360 overhead flip with it before (secured with belts) but the simple rope-tie-solution in the picture wasn't exactly ideal.

Therefore I've made this contruction on both sides:



Two metal slides with a hole each (additionally screwed onto the gondola through several tiny holes, not included in my diagram), a screw through the holes, fixed with screw nuts (self-securing). The hinge is formed by a "ring screw" the main screw runs through. The ring screw is NOT screwed onto the screw, its winding is bigger and it can rotate, or more accurately, the main screw can rotate within the ring screw that is attached to the rope as the gondola rocks back and forth.

I find this construction to be working fine, my only concern is the thickness and durability of the screw. It's an M8 Screw ( A W 8.8 ), I also got a harder ( 4 F 10.9 ) screw from a shop specifying in screws. Yet noone can tell me for sure whether the screw might break or bend or whether it's big enough to support the weight of a grown up person (~100 kg) + gondola (about 20-30 kg) + centrifugal forces. I'd get a bigger one but the ring screw doesn't appear to be available in sizes bigger than M10 and it needs to be bigger than the screw for it to rotate around it.

The whole swing concept ain't all that safe for sure, but I'd like to know whether the screw is a potential weak point and what I might be able to do about it.
 
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Old 07-08-10, 10:39 AM
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I wouldn't worry about the grade 8 hardware being a weak point in this ...application. What do you see in municipal parks holding up tire swings? 1 bolt.

It's a shopping cart with a racing seat dangling from a tree. Why do you figure this to be the only possible weak point?
 
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Old 07-09-10, 03:30 AM
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The "ring screws" are called eye nuts and eye bolts. Your drawing shows an eye nut. They are available in many sizes and much larger than M8 & M10 though they are probably not stocked at your local store. Check industrial fastener suppliers like MSC (Manhattan Supply Co.) or Fastenal.

Since most eye nuts & bolts are intended for overhead lifting quality ones are incredibly strong when the load is directly opposite the threaded portion (like pulling straight up). Their load capacity drops off rapidly with the load is applied at an angle or from the side but since they are usually used for lifting very heavy things they can still handle a quite large load from the side. Just beware of inexpensive ones imported from Asia.
 
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Old 07-09-10, 11:20 AM
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Originally Posted by Pilot Dane View Post
The "ring screws" are called eye nuts and eye bolts. Your drawing shows an eye nut.
It was called "Ringschraube" in the Bauhaus-Store I bought it in (Germany), so I just translated directly. But yes, google image search shows me that eye nut is what I have.

Originally Posted by Pilot Dane View Post
The "ring screws" are called eye nuts and eye bolts. Your drawing shows an eye nut. They are available in many sizes and much larger than M8 & M10 though they are probably not stocked at your local store. Check industrial fastener suppliers like MSC (Manhattan Supply Co.) or Fastenal.

Since most eye nuts & bolts are intended for overhead lifting quality ones are incredibly strong when the load is directly opposite the threaded portion (like pulling straight up). Their load capacity drops off rapidly with the load is applied at an angle or from the side but since they are usually used for lifting very heavy things they can still handle a quite large load from the side. Just beware of inexpensive ones imported from Asia.
I didn't worry so much about the eye nut but about the screw, for that same reason (sidewise-pull) - however I was offered by a friend to drill into the eye nut's M10-winding with an M10 drill, which will hopefully result in the winding being "smoothened out"/removed so I can run an M10 screw through the hole which should be less likely to fail and more likely to turn within the winding-less loop.

Originally Posted by mickblock View Post
It's a shopping cart with a racing seat dangling from a tree. Why do you figure this to be the only possible weak point?
:Homer:

Yeah you're right, the technical control board wouldn't approve. Ha! I know I can't make it safe but I can make it safER ... a bit.
 
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