Need shifting transmission layouts/ideas

[sanddrag]

I should be able to do this myself (since I have before) but I can't come up with anything I like that works well. I need some new ideas because nothing I've come up with has enough reduction while still maintaining elegant but simple design. So, I'm asking for help.

We need a 2 speed dog shifting transmission that accepts two small CIM motors as the input. The no load output speed in high gear must be in the range of 450-500 RPM (slightly higher or lower is okay) The difference between high and low gear needs to be in the range of about 2.5:1. The gears will be 20 pitch. The goal is to keep it as small, as light, and as cheap as possible.

So, if anyone has a good layout that will get me down to this RPM, I'd love to see it.

By layout, I mean gear placement and tooth counts.

Thanks so much.