Sunday, October 31, 2010

This Weekend's Project: Reworking the TF2 Rocket Launcher

This weekend's project comes from the pile of "looked ok 2 years ago, but looks like crap compared to newer stuff" programs. The Soldier's rocket launcher has been a simple and primitive build. The paint has been very lackluster. However, there was little improvement possible for the build, leaving just a new paint job and maybe a few extra polygons.

Here's the 2008 prototype model (top), compared with the 2010 production model (bottom). Major changes include the less-half-assed construction, increased weight due to a liberal use of Magic: the Gathering cards for a stiffer build, thinner inner barrel diameter, and the addition of a firing mechanism.

Yes, this model fires out projectiles.

The Mechanism
Let's go build ourselves a working paper rocket launcher, shall we? First, let's explain a few things. This mechanism is a simple, using a total of two moving parts: a trigger and a launcher rod. There's two springs, easily obtained from mechanical pencils.

 The mechanism works by the use of this odd shaped metal wand and a wooden 3.175 diameter dowel with a 6mm diameter head. The barrel diameter is 6.35mm, giving the rod enough clearance to move around freely.

 The rod fits in a slot that runs through the diameter of the barrel.

 The part that dips low at the top between the "ears" obstructs the head of the launcher rod from moving. Pushing the metal wand upwards into the slot in the barrel allows the dip to slide into the barrel wall, leaving the barrel clear. It's a simple mechanism that is reliable and fairly easy to build. The downside is that it requires a large diameter barrel to make good use of it.

The Build
You'll need the following schematics for the major components:

You'll need the following tools:
  • This excel spreadsheet from this explanatory post explaining how to make cylinders out of paper 
  • 110lb cardstock (don't even bother using printer paper)tack of Magic: the Gathering cards (or structural equivalent, Yu-Gi-Oh! cards need not apply.)
  • X-Acto knife and a cutting surface, and regular scissors
  • ruler
  • Sandpaper (coarse grit at a minimum)
  • Elmer's glue (any strength, but not a Glue Stick), and Super Glue of any type
  • Paper clips (smaller the diameter, the easier)
  • One 1/8" (3.175mm) diameter wooden stick
  • Guide to building with Magic: the Gathering cards (optional)
  • Pliers (Jewelry Beadmaking pliers HIGHLY recommended, regular needle nose pliers mandatory)
  • Badass paper clip bending skills
The level of involvement of Magic card use for this project is minimal and borderline optional. There's only one part that requires cards, and it's pretty easy. The biggest challenge will be your ability to bend a paper clip to this following component:

 This is the key to a successful construction. The closer you are to the dimensions, the better the result. The two legs of the wand have a little protrusion for holding the end of the spring between the head and the middle of the wand. Without that small protrusion, the wand will slide out of the handle, and the spring won't have anything to push against. Your success will depend on whether you can replicate that out of a paper clip. Hope you bought that 100 pack. Don't even try it by hand.

About building the wand: Use a beadmaker's jewelry pliers with thin rounded tips to initiate small bends. After the bends get close to a "U" shape, compress the entire "U" together with needle nose pliers. You'll have two chances to get it right. You can usually undo the bend once before the metal is too fatigued and snaps apart with a second attempt.

About the spring: start from the wand's open end and take the termination end of the spring coil and thread it around the two legs. Spin the spring around until it eventually screws into the region. You should be able to compress the spring while it sits in between the wand head and the protrusions in the middle without any obstructions.

Building the components

 The center object is the trigger housing. The housing preferably should be made of Magic cards. The side wall is 2 cards thick, and the thin walls are 3 cards thick. A plastinated wall made of 110lb cardstock and enough super glue permeating through it may be acceptable, but is very messy. The center of the trigger housing has two walls protruding inside the trigger pathway. This is there to keep the trigger from falling out too far. May be critical if your spring is too stiff or too long for the wand. This, and the bottom of the trigger will be the only parts that Magic cards are helpful for, but can be done without.

 Now if you've built all the pieces, you should now have the following items:
 These are the major components needed. Anything not mentioned in the drawings is stylistic and not structure critical. Depending on your spring length, you may need to either trim it down or change the dimensions by pushing back the rear end stop into the conical part.

The sight works better if you use Magic cards. I did it with 110lb cardstock 2 years ago and it was acceptable.

 The rear part of the launcher is made of three conical sections. You can put them together by making cones or carving down a cylinder. Not structurally important, as long as it stays together.

The build is mostly tubes and squares. A simple project by normal means. I recommend doing some test fires before gluing both halves together. Always good to verify the mechanism works reliably now than have to redo a section later because of a failure. The mechanism isn't the best, but it's effective. You will need to push the trigger in as you load the rocket launcher so the head can clear the obstruction. I haven't tested out other means of assisting the load mechanism, but there's some room for improvement.

After you've assembled the rocket launcher, you'll want some rockets. I recommend making generic projectiles 5mm in diameter and fairly long so you can push the launcher rod in with it. They go fairly far using mechanical pencil springs, despite my reservations.

Happy blasting! (Now with video!)

1 comment:

Anonymous said...

This is just awesome! Thanks, I've been trying to do something like this for a wile.