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How to make an automatic shooting mechanism for a robot?

It's a small robot and it needs to shoot marbles, its a combat robot, so it needs to shoot with high velocity and the shooting mechanism needs to be automatic. It should keep shooting marbles until the motor, or something else, stops any ideas on how to make this mechanism.Just like the one in the link below:

http://www.youtube.com/watch?v=P8sBvgOQHX4

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Depending on how you are building it, feeding the marbles between a pair of spinning wheels is probably a better and more reliable option, perhaps with a slow turning paddle wheel to feed the marble in one at a time.

The mechanism in the video presumably consists of a spring loaded pin, and a reciprocating arm with a latch an it. The arm moves forwards, and latches onto the spring loaded pin, then pulls it back, allowing a marble to fall dawn from the magazine in front of it, then when the arm is all the way back it hits something that causes the latch to release the pin, ejecting the marble. You can drive two of these 180 degrees apart from the same motor to get nearly twice the rate of fire as pushing the arm forward again takes very little effort.
Wisaam (author)  The Skinnerz4 years ago
Which mechanism do you think will shoot the marbles with a higher velocity compared to the other, the wheel's mechanism or the spring?

And can you please explain the spring loading system in a bit more detail or you can just give me a link.
If you use a suitable motor, the spinning wheels will be faster and would probably get a better rate of fire. However, if you are building it out of lego using the normal motors, the spring system is the only practical option for anything heavier than matchsticks.

Have a look at some repeating crossbow designs, it's the same sort of thing, except in this case the bolt stays stuck to the string/elastic and is used to push the marble down the barrel.
Wisaam (author)  The Skinnerz4 years ago
Don't worry, ignore my previous reply, I found a way, thanks.
Wisaam (author)  The Skinnerz4 years ago
Okay, thanks. I took a look at the repeating crossbow designs and lets say I make a little one, how would I connect it to the motor?,I don't think the piston action would work.
I full screen and took a better look at the mec in the robot.

It is a motor driven crank that creates a piston action and the piston sends the marble flying.

Try a Solenoid Gun it does the same thing but faster although he calls this a coil gun this is a solenoid gun see the youtube.

http://www.youtube.com/watch?v=eHv33mH6Nq0
Wisaam (author)  Josehf Murchison4 years ago
Holy crap!!! I made one and it shoots with a very high velocity, but I have problems with turning the coil off at the right time, I have to do it manually, I only press the switch to the coil for second and the iron nail shoots out, I don't have any IR sensors so is there any other way I can make the turning off of the coil automatic?
Don’t you just love the video, his is wicked, he uses a 555 timer driving a transistor.

However if you are not into electronics you can use a momentary switch (a switch that is on for only a moment even when you are holding it down.)

Also a high current switch as strange as it sounds the switch may be temporally welding shut.

Draw me a circuit and I can be of more help.

Best answer me.
Wisaam (author)  Josehf Murchison4 years ago
Well, thank you very much, I now know more because of you, no doubt it packs a lot more punch, I have seen and tested it myself, but it requires a lot of power, and I don't have any battery that could provide that much power so I have to connect it to the mains through a charger of high power. And if I had the battery I am guessing that it would be very large and wouldn't be able to fit in my small robot, If you have any solution to this problem in mind then sure I will best answer you, by the way, I am still having problems with turning the coil off.
Try a finer Magnetic wire and more turns it will bring the current down.
Wisaam (author)  Josehf Murchison4 years ago
I have used a wire, thickness is almost the same as a hair, but it burns up instantly, I did wrap enough of it I think, about a 100 turns. If I decrease the current than it doesn't burn but the magnetic field strength decreases significantly.
This is my first coil gun

I am building a bigger and more elaborate one with 3D printed parts.

It works good the coil is 250 turns of 24 AWG wire.

This works by taking 3 volts and busting it up to 200 volts and storing it in capacitors.

When you depress the button it triggers big the transistor firing the coil.

Are you running your coil off the mains?

You gave me an idea for an instructable on how to get magnetic wire though.

Thanks

Joe
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