Junkyard Wars, possible show challenges

[Pastfinder]

Let's try:
-Build a functional tank
-" " droid
-" " Robo-dinosaur
-" " rocket

any more ideas?

 

[Pretender]

A gun. The target will be both durable (maybe a block of wood) and small, and the challenge is to break the target. Now that's a challenge.

 

[GL]

Build:

-a submarine capable of completing an obstacle course
-a demolition derby car
-a hot air balloon