Shooter
Close-up of shooter right after shooting ball.
The shooter was designed with robustness and simplicity in mind. Conventional baseball pitching shooters would require the use of encoders to close the loop. Rather than build something that complex, our team used a stainless steel ruler (15 in cut in half) that acted as a spring board. A high-torque servo (Hitec HS-485HB) with an extended horn cocks the ruler to the same displacement each time (the servo swings through the ruler, releasing the ruler once the spring displacement is equal to the length of horn), ensuring a constant force imparted on the ball each time.
The v-blocks that the nerf balls sit in before they are shot out are just a little smaller than the balls themselves. This allows them to sit on the extension that comes out of the v-block (the extensions do not interfere with the path of the ball). As the ruler is being cocked, the ball sits further into the v-grooves, making 4 points of contact. These 4 points of contact are of course consistent, which coupled with the constant force imparted by the ruler, allows for a very precise shot.
The shooter can be adjusted in four ways for calibration: (1) to control trajectory, the angle of the whole module (from 15 to 30 degrees); (2) to control spring stiffness, the amount of ruler sticking out as a spring board (usually approximately 5.5 inches); (3) to control how much the ruler is cocked, the placement of the bottom piece that the ruler is attached to with respect to the servo (the bottom piece can slide in the slot shown in the right CAD drawing); and (4) the length of the servo horn that determines the deflection of the ruler.
The v-blocks that the nerf balls sit in before they are shot out are just a little smaller than the balls themselves. This allows them to sit on the extension that comes out of the v-block (the extensions do not interfere with the path of the ball). As the ruler is being cocked, the ball sits further into the v-grooves, making 4 points of contact. These 4 points of contact are of course consistent, which coupled with the constant force imparted by the ruler, allows for a very precise shot.
The shooter can be adjusted in four ways for calibration: (1) to control trajectory, the angle of the whole module (from 15 to 30 degrees); (2) to control spring stiffness, the amount of ruler sticking out as a spring board (usually approximately 5.5 inches); (3) to control how much the ruler is cocked, the placement of the bottom piece that the ruler is attached to with respect to the servo (the bottom piece can slide in the slot shown in the right CAD drawing); and (4) the length of the servo horn that determines the deflection of the ruler.