Simmechanics : how to use the actuating force?

Dear all,

I have the 2 following problems with using simmechanics :

i)I am trying to use simmechanics to act with a sinusoïdal force on a prismatic joint. I use the following configuration.

Unfortunately, when I run the simulation the mass just mooves in one direction and don't oscillate around the zero position. Does someone have an explanation.

ii)When I try to actuate the motion and not the force, I get the error:

 _
"In the dynamically coupled component containing Prismatic Joint Prismatic_Joint, there are fewer joint primitive degrees of freedom with automatically computed force or torque (0) than with motion from inputs (1). The prescribed motion trajectories in this component may not be achievable. Solve this problem by reducing the number of joint primitives with motion from inputs or increasing the number of joint primitives with automatically computed force or torque. Resolve this issue in order to simulate the model."_

I don't understand why I get this error

Thanks for all the help you can provide.

Answer 1

[Swarooph]

Take a look at this documentation. When you set the actuation mode in your joint block, set the Force to Automatically Computed and Motion as Provided by Input. Force/Torque cannot be set to None when joint primitive is mechanically actuated (as shown in the picture in the doc link above). Snapshot below:

[edamondo]

Okay, now I know why (ii) wasn't working, thanks for that. But why isn't the movement sinusoïdal if I apply a sinusoïd force one the object? (I putted no gravity in the model). In other words, if my force is like that :

Why is my velocity like that? :

shouldn't it be going in the negatives as well?

if z''(t)=sin(t) than z'(t)= -cos(t) so it should also go in the negatives no?

[Swarooph]

Can you attach the model? Is your input force or motion? And I also want to make sure you are measuring velocity and not 'actuator force', because your screenshot in the original post shows you are measuring actuator force..