Abstract: A down-pressed clamp base includes: a main body having a space and a passage in communication with the space via a connection perforation; a transmission member fitted in the connection perforation; a leverage mechanism including a lever and a link, the link being pivotally connected with the lever and positioned in the passage, a free end of the link being directed to the transmission member; a fastening mechanism disposed in the space; and a string holding mechanism disposed on the main body for holding a racket string. When pressing down the leverage mechanism, the clamp base is fixed on the racket stringer in an operation mode meeting ergonomics. When the leverage mechanism is pressed down, the action forces of the lever, the link and the transmission member fall on the same straight line, whereby the clamp base is fixed on the racket stringer by a fixed fastening force.

Abstract: A ball-throwing machine includes a frame and a ball-throwing mechanism pivotally connected with the frame. The ball-throwing machine further includes a circuit unit. Via a first servomotor and a first linkage, the circuit unit serves to move the ball-throwing mechanism to a ball-throwing angle and drive the ball-throwing mechanism to continuously swing up and down. The frame can be pivotally mounted on a base. Via a second motor and a second linkage, the circuit unit serves to drive the frame to horizontally swing back and forth. In addition, the ball-throwing machine has a safety switch. When setting the functions of the ball-throwing machine, a user can press the safety switch to stop the operation of ball throwing so as to protect a person from being incautiously hit and injured. The circuit unit further has a malfunction detection function for detecting whether the ball-throwing machine works normally.