How to create Force output with expressions

Davide_21943

Hi, 

I have a simple spring - mass system where a Force = 1 N is applied on the CM of the body. 

I'd like to plot the stiffness, but I don't know how to do it. 
I can't plot the force either. I create output, select expressions, in F2 I type the expression `FX({pmb_0.cm.idstring})`.

I select the CM marker of the body but the output is zero. 

If I use the predefined Force output I can see that the force is 1 N, as it has to be. 

Ganesh Shanmugam

Hi Davide,

Stiffness is an input parameter to define the spring. To just plot the input value you can use `{sd_0.k.lin}` in expression of output request. In case you want to verify MotionSolve result you can scale spring displacement with stiffness and see if it is matching with force, since your damping is zero.

For plotting force, there are may ways to create output request but since you have already created force on body Point Mass Body 0, you will have all forces on Point Mass Body 0 in abf, mrf file for plotting.

You can see this under marker force , Req/70000001 SpringDamper 0 on Point Mass Body 0(Force), Req/70000002 Joint 0 on Point Mass Body 0(Force) and Req/70000003 Force 0 on Point Mass Body 0(Force)

Regards,
S. Ganesh