HELP with a timer, and an actuator

OK. I am Trying to build a Pitching Machine. I have very little electronic experience but I learn quickly. this is what I am trying to do. With this pitching machine that is going to be portable with a 12 V abttery attached. I want to put a Wheel onto a 12V motor, and launch the ball with friction. here is what I need. I want to have a shoot that will hold like 10 to 15 balls and every 5- 15 seconds a ball rolls out the shoot and goes through the wheel (gravity fed) but I need an adjustable timer that will allow me to turn a knob on the outside of the machine and adjust from 5 to 15 seconds. I think I might need a 555 but help me out on how to build it! also the way I want the shoot to work is have all the balls alligned and have some sort of metal rod sticking out holding the balls in place, and then maybe with a neg or positive charge from the timer the rod falls back into place allowing a ball to pass by. I have seen these on automatic shift assemblys on cars so you cant remove it from park when the key is not present. maybe you guys might have a better idea as to how to hold the balls in the shoot. any help with this 12V portable pitching maching would be great!
turbotec@charter.net
Lance

I found this :
**broken link removed**

I think this might be good for what I am looking for because everything is variable. even the time that my actuator to let the balls pass is variable. anyone know what one of those actuators are and where to get one?? also what do you know or think of this board I linked to?[/url]