Introduction: Smaller Knex Semi-Automatic Revolver
UPDATED: New gun design and instructable steps, 08 april
Minor Update, 12 april: Ive redesigned the firing levers to stop misfires. The changes are very small but important. The very last section has a photo of the modifications.
I agree with the comments saying the gun was too bulky. Ive remade it into a much more compact and powerful design. The first few steps are the same, but theres more ones been added to show the new design. Ive also got a video of the gun firing.
I will begin this with the obligigatory "my first instructable etc....". With that out the way, onto the gun. (by the way, I know my username is spelled wrong).
This gun holds 8 shots, and will fire them as fast as you can pull the trigger. It can fire several types of connector. Using two bands per shot, it fires about 30-40 feet, though It has the potential for much more.
It does not require many "exotic" parts, however you do need quite alot of bands. I needed 19: 16 for the barrel, 1 for the barrel spinner, and 2 for the trigger return mechanism.
The basic idea is that the barrel holds the 8 shots in a ring. The barrel is tensioned by a band which makes it rotate betweeen each shot. When you pull the trigger, a level flicks one shot out of the barrel, and at the same time moves a ratchet which advances the barrel one "click", lining up the next shot. This mechanism can work very quickly- I can fire off all 8 shots in under two seconds.
Note: If you fire this at hard surfaces, it tends to break parts off the ammo. Also, the shots rebound very easily and can hurt if they hit you.
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Step 1: The Barrel
First off you need to make the barrel. Its a pretty simple structure.
The first picture shows how you should fix two elastic bands into the connector(sorry for the blurry photo. The rest are much better). Make this part eight times, then build it up into the barrel shown in the second and third picture.
You might need a different number of bands depending on what type you have.
Step 2: Ratchet Mechanism
This part isnt too complicated, but it MUST be built properly, otherwise the gun can easily jam. You need three of the little black clips. This is the only place they are used.
The first picture shows the forward barrel support. Build it up and set it aside for now.
The second picture shows the ratchet base. Build it up and keep it close.
The third picture shows the actual ratchet. Its very important to use the right number of spacers in between each part.
Now, take the forward support, and clip it onto the ratchet base, then clip the ratchet ontop of that. Pictures four and five show how it should look.
Pictures six and seven show how to build the pivot that moves the ram.
Pictures eight and nine show how to connect the pivot to the ratchet base. When completed, you should be able to make the ratchet rock back and forth by moving the connector.
Picure ten shows the extension of the ratchet rod. This will extendto the trigger.
Step 3: Main Body and Trigger
These steps show you how to extend the body of the gun backwards towards the handle and trigger. Get an elastic band ready for fitting here.
Photos one and two show what you should build as a seperate section, ready to fit onto the ratchet base once you have finished this part.
Photo three shows the trigger lever.
Photo four shows the other side of the frame built around the trigger.
Photos five, six and seven show how to construct and attach the handle.
Step 4: Barrel Tensioner and Trigger
Youre nearly done. The next step is to build the frame which supports the rear end of the barrel and the lever system which fires each shot. Get another two elastic bands ready to fit.
Build the structure shown in photos one and two, but dont attach it yet.
Photo three shows what you should build onto a grey rod (mines orange, its the same length). Photo four shows how it fits in the structure.
Now you can fix the structure on. Photo five shows where it goes.
Build the part shown in photo six, then fix it to the top of the frame as shown in photo seven.
Photo eight shows how this links up to the trigger, and where the elastic band is fitted.
Photo nine shows what you do with the band from the grey rod. Pull it down, round the purple connector and loop it round the blue rod.
Now, take the whole rear structure and fix it to the ratchet you build earlier. Photo ten shows how it should look.
Step 5: Mounting the Barrel
Youre almost done. All you need to do is fix the barrel onto the gun.
The photos show how to fix it onto the shaft. Make sure to use the right number of spacers.
Step 6: Loading and Firing.
First, make sure you are on the same side of the gun as the bands which spring the trigger back. Now, while pulsing the trigger in and out, rotate the barrel away from you. It should turn and you should see the tension band wind around the end of the grey rod. Stop turning when you have done about 1 1/2 rotations.
First test the ratchet. If you squeeze the trigger, two things should happen:
-The levers on top of the gun should quickly flick upwards and then fall down when you release the trigger
-The barrel should click smoothly round a bit.
If you pull the trigger very quickly, the barrel will basically act like a gatling gun and continuously rotate.
If this works smoothly, then you are ready to load up the first shots.
First, pretension the barrel as above. Then get your 8 connectors.
*These steps/photos are from the older gun, but the loading is the same*
Photo 1 shows (with alot of blur) how you hook both bands in the connector and begin to pull back.
Photo 2 shows how the shot should sit on the end of the barrel. Repeat another 7 times.
Photo 3 shows all 8 shots loaded should look.
You should be able to work out how you hold the gun and how you pull the trigger.
Assuming everything is loaded correctly, you can now fire the gun. This is true semi-auto: you pull once, you get one shot. If you pulse the trigger rapidly this functions like a machine gun.
NOTE: The shots fire higher than you might expect.
I have been through several versions of this gun before I posted this one. I think I have eliminated most of the problems with the firing mechanism. However the gun can occasionally misfire. Here is a list of the common problems:
The ratchet doesnt work properly
This is probably down to the ratchet not being built or fitted properly. Make sure its fixed securely onto the base, and that the pushrod from the trigger is the right length.
The first shot sometimes misfires
This is caused by the ratchet holding the barrels in a strange position, and the lever not flicking it off correctly. Normally the rest of the shots will fire fine. I dont know how to do anything about it.
The shots are very innaccurate
The gun isnt terribly accurate, but if the shots are not leaving the gun properly there is a problem. Its usually down to the shots not being loaded well. The most common cause is that the bands are tangled up somewhere. The bands must be under the white clip that hold them to the barrel, and they should extend cleanly back to the shot with no kinks or overlaps.
The barrel stops turning half way through firing
Assuming the ratchet is working, this is down to the tension band running out of tension. Make sure you preload the barrel fully before firing.
The trigger feels very heavy to fire
This isnt really a problem. Its the fact that theres alot of moving parts all running off one trigger lever.
New Firing lever design:
Photo four in this section shows how to modifiy the firing levers to a better design.