hi,
i want to make a shooting mechanisim could any one tell me how to start about with it?
the obkect will be cylendrical and of 30 cm diameter i may need to shoot from a varying distance of .5 to 2 meters
Thanks in Advance 
You're going to have to give a bit more detail than that. Mass, material, etc. You say its a cylinder, and 30 cm in diameter, but not its length? That's a pretty big object, anyhow - when I think "shooting", I think longer distances than 2 meters (something that big you would want to send at least a several 10's of meters, if not more). To be honest, I am not sure what you are shooting, what you are shooting -at-, what the object is that is being propelled, what it is made out of, what its true size/mass is, etc. Lots of unknowns...
the obkect will be cylendrical and of 30 cm diameter
That's what you're shooting at, or the object you wish to project?
Sorry :-[
the object is of a height 1.2 meter and coming to mass not yet known but its made of somewhat thick cardboard so weight may not matter
when I think "shooting", I think longer distances than 2 meters
yeah i guess so but i dont need to shoot that long ;D
and the cylender is not propelled just stand still
Lots of unknowns
no more i guess THANKS
That's what you're shooting at, or the object you wish to project?
I WANT TO SHOOT AT IT
Can you explain how Arduino will come into the picture? Is it the Arduino that will be the projectile or the target?
Ok - so you have a target cylinder made of heavy cardboard or similar material 1.2 meters tall and 30 cm in diameter? Is that correct?
What is it you want to shoot at it? An arrow? A bullet? A paper airplane?
Ok, I was being facetious on that last one...
Probably the easiest thing to shoot with would be an electric airsoft gun.
Basically you open the gun up, and wire on extra leads from the switch (or remove the battery and trigger switch, and wire directly to the motor) to outside the gun body, and then hook those leads up to a relay or transistor/mosfet which can then be used by the Arduino to activate the motor (or, if that is too complicated, you could buy a motor driver board/shield, or a relay board/shield - to control the motor).
Once you have that set up, then it becomes a matter of figuring out how to mount the gun to whatever you have aiming it...
Can you explain how Arduino will come into the picture?
this is not essentially related to arduino ( though the project itself involves an arduino)
i asked it here cause there are many people uot ther who know a lot and might b also have some expeirience in this matter
Is it the Arduino that will be the projectile
NO
or the target?
How can a target be a projectile ? 
Ok - so you have a target cylinder made of heavy cardboard or similar material 1.2 meters tall and 30 cm in diameter? Is that correct?
YEAH !
Probably the easiest thing to shoot with would be an electric airsoft gun.
yes i had the same idea BUT its for a competition and its not allowed
any other ideas?
You could shoot it with a camera.
You could shoot it with a camera.
LOL NICE one
return to my questuon pls
could any one tell me how to start about with it?
Start by defining:
a. What projectile you need to shoot. A ping-pong ball? A live mouse? A space shuttle?
b. How far it needs to travel.
c. How fast it needs to travel.
So far, you've only specified one of these.
From there you can move on to what options you have for getting the energy to propel the projectile. Muscle energy stored in a spring? Batteries? A.C. mains? Gunpowder? Rocket fuel?
+1
I'm VERY confused. So far all I know is you want to shoot "something" at a big ass cardboard cylinder.
You asked about this project a month or two ago.
You were told that it wasn't really an Arduino question a month or two ago..
and i replied that i dont want it to be totally based of arduino just i do image processing and send commands to the arduino to make it control things
and comin to shooting mechanisim
i've seen about solenoids spring's and other such mechanisim
i just wanted to know if any one could provide more info about such things
want to shoot "something" at a big ass cardboard cylinder.
and that something can be anything but just
speed anything between 1 to 3 m/s and the accuracy is main factor
now i guess i can hope some answers
ah !
From there you can move on to what options you have for getting the energy to propel the projectile. Muscle energy stored in a spring? Batteries? A.C. mains? Gunpowder? Rocket fuel?
Battery power
How can the projectile be anything?! I'm going to start doing some calculations. I'll be using cr0sh as my test projectile. cr0sh - what do you weigh in your human canonball outfit?
Give us a clue...
http://www.thinkgeek.com/interests/techies/8a0f
Is this what you want... you might just need to buy one.
oK making it a bit clear it can be anything lke a ping pong ball or a peice of wood but the reloading mechanisim is important i would like to keeep it simple
http://www.thinkgeek.com/interests/techies/8a0f
no this is not what i want
It's still not clear where the Arduino comes into this, but the following is some psuedo code that might help.
with PVC pipe
 do until no ping pong balls
   place ping pong ball in one end
   point other end at big cardboard thingy
   take deep breath
   blow like hell into end of pipe
 end do
 ping pong balls --
 if ping pong balls != 0 reload
end with
Do you need the reloading to be mechanised as well as the firing?
Using the ping pong ball and PVC pipe your reloading could possibly be just another piece of pipe at right angles to the barrel that acts as a hopper. Then maybe use compressed air to fire the balls.
Rob
newbie doesn't appear to want to do his own research. He seems to prefer having others do his work for him.
richard thats not the case i thought here there might be some people who have aldready tried this and could tell me something more
and ..
iam doing my bit of research