pic: REV Robotics building system

[Greg Needel]

Originally Posted by MechEng83

I'm pretty sure the discussion is about AREA moment of inertia (units of [length]^4). Though your description of mass moment of inertia (units of [mass]x[length]^2) is related to rotational inertia, it's not germane to this discussion.

Regarding OP's question:
We found the extrusion to be heavier than the thin-walled tubing we've previously used for frame elements. Are you possibly referencing 1/8" wall square tubing? If so, I'm fairly confident the tubing is stiffer in bending and torsion than the Rev Extrusion. As far as axial stiffness (along the length) it's going to be proportional to the cross sectional area, which is proportional to the weight/unit length for the same material.

FYI the for REV extrusion are as follows.

Cross Sectional Area: 0.38133 in^2
Moment of Inertia X: 0.03394 in^4
Moment of Inertia Y: 0.03394 in^4
Yield Strength: 21000 Lbs./ sq. in (psi)
Modulus of Elasticity: 10007000 Lbs./ sq. in (psi)


The debate as to which is stronger really does depend on your loading conditions and use case. If you are talking in the context of FRC style robots, I highly doubt you will see a notable difference in strength per piece (as small deflections) don't really effect much in this case.

Where you will see the difference is in how you join them. A welded 1x1 tube is going to be better than a piece of extrusion with nuts and gussets, but there again it depends on your use case and for FRC scale applications you can't go wrong with either.