These are some CNC patterns that are widely used in robotics to lose weight on the robot.
You forgot the standard cheese hole!
Plain circles work just fine as well. They are so much easier and faster to produce, especially on CNC turret/punch machines, and even more so when the machine shop is donating their services for free. Giving up triangulated hole patterns that would require a lot of “nibble” punching for standard size circles which are punched out in one shot makes them a lot happier.
http://www.team228.org/gallery/58/slideshow/bds-22.jpg](http://www.team228.org/media/pictures/view/2648)
http://www.team228.org/gallery/61/slideshow/weeksix-115.jpg](http://www.team228.org/media/pictures/view/2930)
Art these are just some patterns that I saw teams CNC out in Atlanta and other comps. The cheese holing is a pattern commonly used and everyone knows of it.
Art, what your pictures are missing, are the burrs from the hand drill used to make them on-the-fly on the side of the inspection table while you are trying to lose .2 lbs 
On the serious side, those are some nice circles in your chassis pieces, Art. Very very professional and nice looking.
And regarding the original poster’s design, these types of holes look very appealing, and I’m sure they will be a takeoff point for many CNC fabricated chassis’ that wind up getting designed here :] Nice work!
Jacob
I can’t take credit for that chassis design, as that chassis was mostly from 228’s previous mechanical engineering mentor. However, I will be working with the students and other engineering mentors on 228 over the fall to prototype a similar frame design for potential use in future years, as we really liked working with CNC sheet metal designs. Ideally, our goal is to design a modular chassis that will need minimal tweaking each year, much like that of 25 or 173.
But the main reason why those holes look professional is because they weren’t done by hand; they were made on a CNC machine - hence the reason why I posted them in this thread. 