I have done that, it works well, if rather inefficiently. Just remember to use steel endcap bearings, or remove the rubber endcaps, otherwise there will be fun. Works best using a 12V car battery, and around 5m of 2.5mm bare steel wire as a ballast resistor. The wire glows red during startup ( until you move the shaft to start) and then cools down to just burning hot but not glowing. The motors generally will run for 5 minutes before something fails, either the cage melts, the balls drop out or the raceway arcs enough to seize.