Imagine that there is a spring, with a known force constant, diameter and stiffness, as well as a known length. The spring is under tension. I want to quickly change the length of the spring by changing the number of 'active' coils (the coils that are able to decompress/compress freely), so that the force constant changes (as it is inversely proportional to the length).
So, what ways can the length be varied? Are there any known mechanisms that do this?
A progressive spring works like that by allowing a few coils to contact first before the rest do as the spring compresses. In effect, this reduces the number of active coils increasing stiffness. The result is a non-linear force curve.
yes, there is a way, as follows.
Imagine the spring is hanging vertically in front of us. On its lower end we attach the loading arrangement and in the customary way we hook a suspension string onto its upper end and hang it from the ceiling.
Now we modify this arrangement by squeezing a rod sideways into the space between two adjacent coils of the spring at that number of turns that we wish to "disable". Then we put a hook on the end of the suspension string and run the hook down into the center of the spring until it catches the rod.
If we now load the spring, all those coils that are "above" the rod are out of the equation. by unhooking the string and moving the rod to another space, we can add or subtract active coils at will.
