How do you apply spin in a table tennis ball launcher?

I am currently constructing a table tennis ball launcher and the design is effectively, a feeder tube leading to a box which has 2 motor-operated flywheels at the front which project the ball out. Has anybody got any ideas on how i can add various spin to the ball?How do you apply spin in a table tennis ball launcher?
Go online and look at airsoft guns using a ';hop Up'; type barrel. They use a small rubber ';O'; ring and the backspin can be adjusted by moving the o ring mount, as the bb passes it starts a spin in the oposite direction. Same principal would apply just on a bigger than 6mm scale.How do you apply spin in a table tennis ball launcher?
You can rifle the barrel, or form a cardboard barrel using the spiral pipe manufacturing method.



Another possibility: glue a thin strip of #600 or #1000 sandpaper on the inside top of the barrel. Also, construct the barrel so it can be rotated relative to the breech -- that way the spin orientation can be changed.



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