[philso]

What happens to your frame when you apply a compressive force on two diagonally opposite corners? It seems that it is the two U-shaped pieces of square tube that keep your chassis from "parallelogramming".

Is there a reason you chose to use two u-shaped pieces of bent tubing vs. a single straight piece down each side? It seems that the manufacturing tolerances (bending cutting drilling) would have to be pretty tight to keep the six axles parallel to each other. How are the axles for the front and back wheels attached to the two left/right frame members? The holes for these four axles are not perpendicular to those frame members.