The Platform

A fast and easy way to create the 3-dimensional shape we need is to cut a single outline that will be folded into the desired shape.

You have some freedom here, you're not necessarily constrained to follow this example exactly. Any shape with a handle and enough real estate to mount all the electronics on will work just fine.

Cut holes for Motor

Draw the outline of the motor on the edge of the cardboard. Be careful not to position it too close to the handle.

Cut a space for the motor hub to fit.

Cut another hole in the top for the wheel to poke through. This should be long enough for the wheel to poke about 1/4" through the top.

Launching Tube

Cut about 2 inches off the end of a cardboard tube from a paper towel roll.

Cut a small gap from this short piece of tube.

Glue this section of tube over the hole cut for the motor's wheel. This will hold the ping pong ball in place so that the spinning wheel can launch it.

Ping Pong Ball Magazine

Using the remaining length of cardboard tube, trace an arc along the bottom approximately the same diameter of the ball you plan to launch.

Cut along this line, testing that the ball will be able to squeeze through it, but not fall out too easily. 

Glue this to a rectangular section of scrap cardboard (this can be trimmed down later if needed).

Guard Rails

Glue two thin strips of cardboard along the sides of the launcher. This will keep the ping pong balls on course.