Help with auto jelqer

Hi, a few months ago I posted about an auto jelqer. Since then my best idea is using a small device. This is combined with the pro extender and just needs to move a tight ring that grips the penis shaft. The ring moves up and down the penis shaft. Its quite simple with a fixed distance to move and would be mains charged. Has anyone got an idea of what the device could be? It needs to be small, mains charged and be able to move up and down constantly. Thanks