[ChrisH]

At 1.4"x1.4" just about any wood should be sturdy enough for this competition, no matter how it is made. The problem is probably something else, like a weak attachment.

So the first thing is to make sure you have at least two bolts or other fasteners arrainged along the pole axis at each end. Side by side fasteners will not do as they tend to create a pivot point, you want a line.

Then break up any rectangular open spaces into triangles by attaching something diagonally across the corners. 1x1x1/8 aluminunm is great for this. If you want you can use cable, but then you have to go both ways. Metal pipe hanger tape will work too. Both are pretty light if weight is an issue. This will dramatically stiffen your structure.