Apparatus for target practice comprises a parallelpipedal body containing a motor, and a drive shaft emerging from the body and carrying a crank. Swingably mounted on the body is a shaft having cross arms thereon, one of which is connected by a link to the crank and the others of which can selectively...http://www.google.com.hk/patents/US4288080?utm_source=gb-gplus-share專利 US4288080 - Apparatus for target practice
