We only used the idlers to get some extra height to get over the battery-pack (shorty cross-wise)
As far as trying to get motor-rotation "right", we decided not to further complicate things and just see how the rotation comes out.
@DCM : who knows
never seen lid-off shots of an X-7
In the meanwhile I've updated the design with some tabs for a topdeck and done some work to space out the gears inside :
