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