An automatic fetch machine is a dream come true for many dog owners who have overly energetic dogs. Certain breeds such as golden retrievers, Labrador retrievers and wheaten terriers have boundless energy. Playing fetch is a great way to burn off that energy, but some dogs will play for hours. An automatic fetch machine is a great solution to satisfy dogs that have boundless energy.
Begin by building the circuits with the switches. Hook both relays onto the motor, with one on the positive and one on the negative. Hook the negative side relay onto switch 3's NC Side, and in a joint connection (with the positive side's com side) from the com and no nodes onto switch 3's NO side. Connect the positive relay from the NC to the com on switch 2. Connect switch 2's com to the no on Switch 1. Connect switch 1 to the 12 volt power supply and connect switch 1's NC to Switch 3's com.
Assemble the skeleton of the launcher with the guide rails. Begin to place the circuitry. Be sure to place the trigger so that it flips the correct switch (switch 2).
Place the slingshot and the ball cup into the assembly by attaching it to the guide rails on the front. Tie the elastic ends of the sling shot to either side of the guide rail skeleton. Check to make sure that all of the parts are connected and that they move freely.
Test the machine with the ball. If it doesn't work, troubleshoot the electrical components. If the motor doesn't turn on, be sure that the circuitry is correct -- same for the switches. If the circuitry runs fine, be sure that parts can all move freely. Adjust tension or add lubrication where necessary.
Almost all of the parts (save slingshot, ball cup and ball) are available from several models of scanners.
Make sure to get a strong enough motor to launch the ball. Conversely, too strong of a motor might launch the ball too far or too hard.