SpudFiles

I am currently making a paintball gun with the same setup of a nelson gun. I want to make the gun reload itself after each shot by pusing the bolt back. My gun is designed to look like a M4. I thought about using the air from the shot to push the bolt back, but I didn't know if it would have enough power. I also thought about using a motor like an aeg.

why not just make a hopper like a real paint ball gun?

Because, I am making it as real as possible. The paintballs come in casing for added effect. I am modeling the gun after the m16 by Rap4.com

ohh ok, never built one of these, sorry

I decided to use the motor like an aeg. I think it will be strong enough if I made my own gear box. Does anyone know how to make the motor be semi automatic because right now the gun will continue to fire as long as I pull the trigger.

I dont think a motor would be enough to launch a paintball, unless its a rather large one. Also, I would buy a gearbox over making one, they tend to be more reliable in my opinion.

To make the motor "semi-automatic", you could try:
1) Pushing and releasing the trigger (assuming you are using a momentary switch).
2) A 555 Monostable circuit.

Found the website with a 555 calculator: http://555-timer.clarkson-uk.com/operation/frames2.html

The motor is not launching the paintballs. It is pushing back the bolt for the nelson gun. I am using an on/off switch.