Help with Swift 3D shading

G’day, I am trying to make a cardbaord box in Swift 3D which I am going to
animate and use as an interface once imported into flash. The box is made
from individual extrusions so I can fold it etc… but I need some help with
shading.

I have tried puting a plane underneathe the objects but instead of giving a soft
grey shadow wich I want it reflects the box?

Here is the type of shadow I want to have

http://www.kirupa.com/forum/attachment.php?attachmentid=37976&stc=1&d=1153635357

Also I need to know if I create a plane to give off the shadow and export the
animation as a .png sequence will it just show the shadow or will it show
the plane as well?

Thanks, any help much appreciated.