Spring gas to open door

Hello,

i would do an analysis to determinate a forze of a spring gas to open a horizontal door.

In my dynamic analysis i have set a linear motor on the spring gas and the gravity force, i would like a output a graph that show the trend to resultant of the forces in function of the opening angle.

My result now is a graph of reaction forze on the spring gas, but it have't the correct trend: i expect a curve showing zero at a certain angle (balance of forces)

Someone have advice?

Thanks