How does the spring system work exactly?

[David Delaney]

I am curious with Cody's design and others, how does the arm/spring system work?  I do understand that when weight is placed against it, the springs create tension and stop it from falling to the ground (correct?).  But what about when you boom it?  How do the springs work then?  Do you need different springs for booming the arm? 
When the arm is boomed (using Cody's design), the springs are doing the job holding it up and out, so that is easy - but when you want to bring the arm back in, those same springs let it stay in a lower position, right?  I am not sure how that works, because it is the strength of these springs that held it out as a boom, wouldn't it natural want to move to one position or another - either booming or down (ie, why they are called springs, because they spring back)?
I am still building, but these thoughts were running through my head last night.  I know it must work because so many people have designed it, but I am just a little confused about the springs and its affect is all.  Thanks

[Cedric Akins]

Well from my experience when your sled is placed on the arm, if you have the proper springs attached to the arm, it should remain in the place where you place it. But once you apply any push or pull, which is booming, the arm and sled should hold it's position to where you set it. If you push the sled down to a position it should remain there until you pull it up to another position. I hope that this was helpful.

Cedric

[Trevor Crump]

Well from my experience when your sled is placed on the arm, if you have the proper springs attached to the arm, it should remain in the place where you place it. But once you apply any push or pull, which is booming, the arm and sled should hold it's position to where you set it. If you push the sled down to a position it should remain there until you pull it up to another position. I hope that this was helpful.

Cedric

This would be the theory on a arm that was perfect Iso-elastic (or pulley and spring system). with most arms that contain single or double springs, the sled will stay in a position that is the natural spring vs weight position (this can be adjusted via spring settings), the booming is achieved by lifting the arm up, or pushing the arm down (sometimes in conjunction with changing body posture), if released, the arm will come to rest back at it's natural position.

Trevor Crump
Australia

[Cedric Akins]

Thanks, I didn't know if he was referring to a 3A arm or a single spring arm. But the info is much appreciated all the same.

This would be the theory on a arm that was perfect Iso-elastic (or pulley and spring system). with most arms that contain single or double springs, the sled will stay in a position that is the natural spring vs weight position (this can be adjusted via spring settings), the booming is achieved by lifting the arm up, or pushing the arm down (sometimes in conjunction with changing body posture), if released, the arm will come to rest back at it's natural position.

Trevor Crump
Australia

Cedric

[michael stevenson]

Trevor is exactly correct.

MS

[Wade Francom]

It's tough to describe the mechanics of the springs and how they work, but here's one thing to remember... springs always want to return to a restful state. That much is common through pretty much any arm, whether a single arm, 3A arm, compression spring arm....whatever. It is the tendency of a spring to return to it's normal state that counteracts the force of gravity on the sled. All arms are engineered so that when the springs are in the most restful position, the arm is boomed all the way up. The arm us under the most force when boomed to the extreme lowest position.

The springs only counteract the force of gravity on the vertical plane, boomin up and down, and have no effect on the horizontal plane (panning).

A well tuned arm will be adjusted so that the spring tension, under the load of the sled, counteracts gravity enough to hold the sled out with the arm sections totally horizontal, meaning it has as much room to boom up as down. This is the "sweet spot". With some arms, the "sweet spot" is adjustable. The more you tightn the springs, the higher in the boom range the "sweet spot" will be. Likewise, as you loosen the springs.

To understand the way the springs counteract gravity, you have to understand a little bit of trigonometry first. I'll use Cody's 3A variation to illustrate...

In Cody's 3A arm, each section is a rectangle, with each corner containing bearings so the section becomes a trapezoid when boomed. His has 3 springs, but I will illustrate with only one spring. Imagine the spring ran from one corner, to the opposite corner. The distance between the 2 corners is less when boomed up, an more when boomed down.  A spring is naturally going to make the section retreat to where the spring is stretched less, booming it up. The 3 spring design is just an extension of this basic principle.

Cody actually has some video somewhere of his rig during construction that perfectly illustartes the workings of an arm.