a power supply unit including {TAIL ~ a rechargeable battery} and a voltage regulator circuit for regulating and outputting a voltage of said battery for supplying power supply voltage to {HEAD ~ said sensor means}, said wheel driving means, and said control means and 
a power supply unit including { TAIL ~ a rechargeable battery } and a voltage regulator circuit for regulating and outputting a voltage of said battery for supplying power supply voltage to { HEAD ~ said sensor means } , said wheel driving means , and said control means and
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH