Gearing a Rotating Arm

[kitare102]

Our current robot design includes a dual-flywheel shooter on an angle-adjustable arm which we are currently trying to figure out how to rotate. For reference, the arm can be approximated by a mass of 3.5kg at .3m from the pivot. Our question is what would be a good way of gearing the arm such that it is responsive. To make another approximation, let's say "responsive" means traveling from horizontal (0 degree) to 45 degrees in .5 seconds, which should really be taken as a guideline over a restriction for the design.

The current model involves a versaplanetary (motor and stages undecided) followed by a sprocket stage which is necessary for the placement of the gearbox but can be made a reduction anywhere from 1:1 to around 4:1. Is a versaplanetary a good choice for this situation? If so, where to go from there and if not, what other options have teams used?