????????? ?????????? ??? ?????????? ????-???? ????????? ????????? ??????????? ??? ???? ??????, ??? ????? ?? ?????????? ????????? ???? ??????.???????? ?????????????? ???????? ??????????? ? ?????????? ?????, ??????? ??????? ??????? ???????? ??????.A relatively recent progress could be the substitute of wheels or steel crawler-kind tracks with flexibl