? ??????? ???????? ????? ??? ????? ?????? ???????, ??? ??????? ??? ???? ?? ????? ??????? ?? ???????? ??????? ?? ??????????:???????? ?????????????? ???????? ??????????? ? ?????????? ?????, ??????? ??????? ??????? ???????? ??????.A comparatively new improvement may be the substitute of wheels or metal crawler-style tracks with flexible, steel-strengt