A chassis with a plurality of support wheels, wherein at least one said support wheel is a drive wheel,
- an electric motor drivably connected to said drive wheel,
- an electric power source,
- a power supply circuit interconnecting said power source and said motor, for selectively delivering electric power from said power source to said motor, including power circuit first and second terminals,
- an activation duration limiting module within said power supply circuit and timed by liquid draining from a drain vessel,
- and a liquid collection tank, and a vessel drain opening creating fluid communication with said liquid collection tank, permitting said liquid to flow gradually from said vessel into said liquid collection tank,
- wherein the presence of a certain minimal quantity of said liquid in said vessel causes said power circuit terminals to make electrical contact with each other and thereby completes said power circuit, activating said motor, and wherein said circuit remains complete and said motor activated until enough of said liquid has drained from said vessel to decrease the quantity of said liquid to a level below said certain minimal quantity, and thereby causes said power circuit terminals to electrically disconnect,
- wherein said first and second terminals are resiliently biased apart from each other, and the presence of a certain minimal quantity of said liquid within said vessel causes a mechanical displacement which closes said power circuit terminal together, and wherein the draining of said liquid to a level below said sufficient quantity reverses said mechanical displacement and thereby permits said terminals to separate from each other and thus to deactivate said motor,
- wherein said drain vessel comprises a vessel side wall defining an open liquid receiving top end and narrowing to a drain opening at the bottom end,
- and wherein said collection tank comprises a tank bottom wall, a tank side wall extending upwardly from said tank bottom wall, and a tank cap structure including a cap structure top wall fitted onto the upper end of said tank side wall, and a downwardly sloping funnel region in said tank top wall with a central funnel opening, said funnel region being encircled by an upwardly extending funnel region side wall, and a lateral opening in said cap structure side wall through which a substantially horizontal funnel lever is pivotally mounted, said funnel lever having secured to its inner end said drain vessel, and said funnel lever outer end including a counterweight mass and terminal contact means, said arm being positioned adjacent to said motor power circuit electric terminals, said terminals being biased to move apart from and out of contact with each other,
- such that said liquid is poured into said vessel, and the weight of the said liquid in said vessel offsets the counterbalancing of said counterweight mass and tilts said vessel and said lever inward end downwardly, thereby simultaneously pivoting said contact means against said first terminal, pressing said first terminal against a second said terminal and thereby closing said motor power circuit,
- and such that said liquid in said cap structure progressively drains through the opening in the bottom of said vessel and into said collection tank, and the combined weight of said vessel and the liquid remaining in said vessel becomes progressively less until a point is reached at which the weight of the counterweight mass exceeds the weight of said vessel and said liquid remaining in said vessel, causing said lever to pivot back to its initial position, and moving said contact means off said first terminal, such that the biasing of said first terminal again separates said terminals and opens said power circuit to deactivate said motor.