I've been looking on the web for concept artists recently to do some artwork for our rulebook and to have items to post on my wall to hopefully help motivate me on to bigger and better things. Or at least to remind me to stay the course.
As I've been doing so I came across a few artists on DeviantArt.com that I think could do a really good job and I've contacted one in Singapore named Kai (http://ukitakumuki.deviantart.com/) whose artwork I've referenced with a link at the bottom. I'd like to someday meet him in person during my travels to a supplier in Johor Bahru, Malaysia.
Another one I came across didn't have as much in their portfolio as Kai did, but it certainly got my attention and I coudl certainly invision the attached 3 pieces of art as a sort of a real life Caltrop piece if you kind of mixed the three:
They are all from the same artist who can be found at this link http://lucid-grey.deviantart.com/gallery/
Obviously mixing them into something with 3 legs would be a really great representation of the game piece as level one pieces. For a level 2 piece I would add a large cannon, level three Surface to Air Missiles on its back and then jet propulsion for a level 4 Caltrop.