The issue is with finding elliptical tubes of specific, particular sizes. For instance, the tube for my current project is 33 x 66 mm; since the original point was to reduce area and circumference of the tube relative to a circular tube that holds the same cluster, it has to be that particular size, or quite close to it, or you start rapidly losing that advantage. This is for a cluster of two 24 mm motors. One could obviously do the same for other motor sizes, and one would still need a rather particular tube size for each motor size. And one might want mandrels for the corresponding couplers, though those could be 3D printed. Ellipse-to-ellipse and ellipse-to-circle transitions could also be 3D printed.
So the issue isn't just where to get elliptical tubes, but where to get the right elliptical tube.
So the issue isn't just where to get elliptical tubes, but where to get the right elliptical tube.