The 4020, 4055, 4056 and 4073 juveniles can all be motorised quite simple using a high quality motor gearbox unit mounted under the baseboard to drive the model directly.
Because these models require so little power to turn them the same motor can also be used to belt drive other juveniles. The adapters for the various rides are made with different diameters so that the models turn at different speeds. Power for these motors can be supplied from a regulated 12volt power supply (I can supply if you do not already have one). Full details are included in the kit instructions.