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Originally Posted by Alex1072
We're using it as a vertical support. Actually you can see the 2x2 in one of the teasers i posted. The other places we want to cheese hole are at the base of our arm (cross bar), and as a vertical tower for cabling purposes.
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The moment generated by the arm needs to go into whatever is holding it up. You also need to consider side loads (like impacts with other robots) that can create torsion around the 2x2. I typically assume a 1/2g side load in addition to the normal gravity load.
Assume that the 2x2 is at the "back" of the robot and the arm swings up and down pointed towards the "front" If you knew it was only going to resist the moment from the arm and gravity, you could probably cut 1 1/2 inch diameter holes in the left and right faces of the tube and space them 2" apart without compromising the strength of the tube in the fore and aft direction. However, I have not investigated the effect of such holes on torsional strength and stiffness. The bolt on rails will also have some effect, but since I know little about them, I can't estimate how much.