For a 5-sided drum (of some length - 3 or 4 balls), I did some geometry calculations to see how things will line up when acting as an intake. Of particular interest is the length of the spacers ("vanes") that separate the balls in the drum. These vanes must be long enough to push and hold the ball when the drum rotates but yet allow new balls from the ground to pass below one when in the intake position. My calculations shows that there is an inch to space even with a full size vane so it's all good.

Summary of numbers:

* Assume a 5 inch diameter ball

* Assume 1/4 inch additional space to account for the thickness of the vane (we probably want some slack too but not too much. How much will balls deform over time?)

+ The largest pentagon we need has a center to vertex distance of 8.65 inches. Due to the geometry of the balls relative to the vertices, we can go smaller (and we probably want to to save space, but this is a good starting point).

+ With one vane perpendicular to the floor, the adjacent vane angled at 72 degree away will leave a clearance of 5.98 inches above the ground. This is enough for a ball to pass under the vane.

+ The smallest vane we can use is on the order of 3.6 inches (actually larger due to other geometry I neglected to add to these estimates). Such a vane would have a clearance of 7.5 inches (less due to estimates).

+ Fitting a circle around the vertices of the pentagon, we have a drum diameter that is twice the vane size or 17.3 inches. This has some wasted space (again from earlier fudge) so in actuality, the drum will be smaller.