This is a typical picture of the gearbox/drive sprocket arrangement. The only support to the shaft is the two walls of the gearbox and the length of the shaft has quite a strong leverage force on those two points.
Now this picture is from a Heng Long Leo2A6
Nothing special here, but with the addition of the plasitc collar it supports the side forces applied to the axle which gives relief to the above mentioned points.
And this is a picture of a mod I did by placing a large ball bearing in the hull side wall.
Ian