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