Contra Rotating Heringbone Gears

*****Caution***** As I currently have no working printers (one under repair ATM) I haven't been able to test the tolerance. I've been working on a project with my kids to study aircraft with contra-rotating propellers, such as the  P51 Racer. I decided to also try and study how to CAD herringbone style gears. These are uncharted waters but I thought it worth sharing as is for now.

Designed to be built with M3 45mm screws and some M3 hex nuts. The small gears are held in place by the frame and the inner and outer gears can rotate. They will move in opposite (contra-rotation) directions. I designed it to be large and give my kids a better hands on experience as we study some of these engineering aspects. This "test" will lead to later, smaller designs that will be attached to motors. For that we will need to get better printers with very high resolution.