Kangaroo help (how to maintain the length of lines when using Springs)

Hi,

I am relatively new to Kangaroo and having difficulties in my project. 

In my project, I want some of the lines and points drop after I click the toggle. Since the length of them are different. I expect some of the line and points will drop further than the lines are shorter.

So I used the Springs and it worked ok. The only problem I have is the length of each line actually change. Is there a way to lock the length of those lines during the simulation?

Thank you very much!!