Dual Disc Launcher

Minor update, 01 may: Very small but significant change to the trigger block mechanism. Photo in the last section.

This gun has two seperate functions:

-A bolt action, 8+ round launcher which can fire big tire hubs about 40-50 feet

and

-A singleshot launcher which fires small tire hubs about 50-60 feet.

The primary mode is pretty simple; you pull back a bolt, and a disc drops into the firing chamber. You pull a true trigger and it fires out. The secondary mode requires you to take a small disc from a store on the side of the gun, put it on the launcher, and manually pull the bands across it. Pulling on a pin fires this disc out. If that seems a bit complicated, dont worry, its very simple and quite fast to reload when you get used to it.

Parts List:

This is an approximate list of parts you need.

25 dark blue connectors
30 light purple connectors
10 red connectors
2 green connectors
12 orange connectors
30 yellow connectors

35 blue rods
50 white rods
5 yellow rods
25 green rods
8 red rods
5 grey rods

A few tan clips and grey clips.

Step 1: Firing Chamber + Magazine

We begin with the platform which holds the discs and the block (ugh) trigger which holds back the firing pin. Pretty simple, just follow the photos.

1: the platform

2,3: this is what supports the load on the trigger.

4,5,6: block trigger

7: build this

8: attach the trigger to the frame

9,10,11: attach the platform onto the trigger

12,13 : build the band supports. important: The purple connectors must be orientated as shown, otherwise the gun will explode when you cock it. And you really dont want that to happen.

14,15,16: This is the magazine which holds the big discs.

17,18: how to attach the magazine.

Step 2: Main Body, Impact Rails, Trigger

We start off with one of the most important parts of the gun: the impact rails which absorb the force of the firing pin. Use good quality rods, ie ones that arent bent, scratched, dented etc.

But first we build the trigger cam system.

1: build this

2: attach as shown

3: keep building

4: Extend body back as shown

5: build supports

6: The impact rails

7,8: Where the rails go.

9: build the frame back and loop a elastic band around the rod.

10: Hook the band round the trigger cam as shown.

11,12: extend the frame back further.

13: The true trigger.

14: attach the true trigger and connect

Step 3: Handle, Arm Support, Secondary Launcher

The handle is probably the single hardest part. I couldnt deconstruct it to take photos, so youre just going to have to work it out.

1-5: The handle. You dont strictly need all the semicircle connectors, but they make it much more comfortable to hold.

6: The arm rest. Simple.

7: The handle and arm rest attached.

8: Take a broken elastic band and fix it on as shown.

9,10: The lower launcher support.

11: The launcher band head.

12,13: Fitting the bands for the launcher.

Step 4: Firing Pin

Almost done. The firing pin is the same one Im sure you have built for 100 knex guns before this one. Im using a small cable tie to secure it.

1,2: The firing pin. Use a tan rod if you can, its much stiffer and will be able to handle more load.

3: Where it goes.

4,5,6: How to fit the bands into the frame.

7: The finger latch on the pin. This design is pretty poor, feel free to improve it.

Step 5: Finishing Touches, Loading+Firing

The last thing is the ammo store for the secondary launcher. Dead simple.

1: Build as shown

2: put on small tires and secure with orange connector.

3: How the big discs stack.

Loading and Firing

The video at the start shows the best way to cock the gun while keeping one hand holding it.

With the discs loaded, pull back on the firing pin until it clicks in place. Photo 4 shows how it should look ready to fire. Then just pull the true trigger.

Design Update, photo 5

Just modify the firing chamber so it looks like this. It makes the trigger and discs much less likely to jam.