Make a Mid-sized (disassemblable) Steel Trebuchet

This is an Instructable to make a trebuchet out of steel, that can be entirely disassembled.   The pivot point is 102.5cm (41 inches) off the ground.  The throwing arm is 180 cm (6 feet) long with a 5:1 ratio.  It was designed and built by me when I was in Grade 12.  Right now, with a wooden arm it, it holds 32 pounds of counterweight, and the arm bends alot.  So I'm soon to be upgrading it with an aluminium arm, hoping to get 50 pounds on it.  It can throw golf balls, tennis balls, baseballs, potatoes (they work really good, the longest shot I've thrown yet was with a potatoe).  When I was throwing rocks, it has a range between 90-100 feet. It has quite good accuracy 10 shots I launched all landed within 5 feet of each other.  I made it at school, so I had access to all the tools in a metalshop, so you might have to improvise if you don't have a full workshop at home.


I'm going to assume you follow the steps in order, so some steps I will tell you to use pieces that you should have built in previous steps.  If you get confused, just go back and make sure you've done everything the previous steps told you to.  Also, it would be good to read through the Instructable before starting anything, and watch the video so you get an idea of how everything should work and how its put together.  But, don't forget to check the bonus step!

I will be telling you to look at Pic #1, or #2, to help you with steps.  The first pic in the step is #1, the second is #2, nothing fancy.  it should be common sense.  Thought i'd explain it just in case.  Ex: On this step, Pic #1 is the side view of the trebuchet, Pic #2 is the front view.  Easy, right?

  PS.Some of the pictures are kind of dark/blurry, as they were taken with my video camera.  Nicer ones will come soon.  

UPDATE!!  My throwing arm broke as I was filming the last video (you get hilarious footage of my reaction.), but that was because I was over loading it.  I built it to withstand 20 pounds, but I was seeing how far I could push it. DO NOT GO OVER 30 POUNDS!  25 would be good to be safe, unless you built a super strong arm.  This will decrease the range a bit though.  

This is all the stock material you need.  Check each step for its material list.  In brackets, I've told you the size of each individual piece.  You don't have to cut the material now, I've told you what to do on each step.  Just make sure the pieces you have are big enough.

MATERIALS:
- 70 cm (28 inch) of 5/8th's inside diameter pipe (Four pieces of 10 cm (4 inch),  four pieces of 7.5 cm ( 3 inch)

- 725 cm (24 feet, 2 inch) of 1 inch wide by 3/16th's inch thick band iron (Two pieces at 150 cm (5 feet),  two pieces at 120 cm (4 feet),  four pieces at 25 cm (10 inch), four pieces at 17.5 cm (7 inch), and two pieces at 7.5 cm (3 inch)).

- 531.25 cm (17 feet, 8.5 inch) of 5/8th's rod. (Four pieces at 120 cm (4 feet),  one 45 cm (18 inch) piece, one 6.25 cm (2.5 inch) piece.)

- 45 cm (18 inch) of round stock that can fit through your safety pipe.

- 11.25 cm (4.5 inch) of safety pipe. (Three 3.75 cm (1.5 inch) pieces)

- 15 cm (6 inch) of 2.5 cm (1 inch) wide steel square bar that is 1.25 cm (.5 inch) thick. (Two 7.5 cm (3 inch) pieces.

- 5 cm (2 inch) of 1 inch thick hexagon stock (1 inch from flat side to flat side) (Four 1.25 cm (.5 inch) pieces)

- 25 cm (10 inch) of pipe that can slide over the 5/8th's rod. (Two 12.5 cm (5 inch) pieces)

- 41.25 cm (16.5 inch) of steel square pipe with a 1 inch square internal diameter (One 40 cm (16 inch) piece, one 1.25 cm (.5 inch) piece.

- 2.5 cm (1 inch) Pipe that the bearings can fit into (I had to wrap a layer of electrical tape
around mine to wedge them in). (Two 1.25 cm (.5 inch) pieces)

- 6 feet of plywood in a 2.5 cm (1 inch) square.

- 30 cm (1 foot) of 1 inch thick round stock

- 18 gauge sheet metal, two pieces that are 90 cm (3 feet) by 35 cm (14 inch).

- 45 cm (18 inch) of 1 inch wide band iron thats 1/8th inch thick. 

- 10 cm (4 inch) of angle iron. (Four pieces of 2.5 cm (1 inch) each)

- Release pin. I took a small piece of 1/8th inch welding rod and sharpened the end, but you could use a nail with the head cut off. It has to be smooth.

HARDWARE: 
- Two Hinges
- Old pair of vice grips
- Large bundle of twine (50+ feet)
- Piece of denim. I used the legs of an old pair of jeans that I had turned into shorts.
- Needle and thread 
- Five 1/4 inch bolts,1.5 inches long
- Two 1/4 inch bolts, 2.5 inch's long 
- Eight 1/4 inch bolts, 1 inch long
- Fifteen 1/4 inch nuts.
- Twelve 1/4 washer's
- Two keyrings
- Wood Screw
- 2 ball bearings with a 5/8th's hole through them ( must fit on the axle)
OPTIONAL:
- Magnets

TOOLS:
- Cutting tool (hacksaw, bandsaw, chopsaw... Something to cut with)
- Drill (Hand drill and/or drill press)
- Centre Punch
- 17/32's drill bit OR 37/64th's drill bit
- 11/16th's drill bit
- 5/8th's drill bit
- 1/4 inch drill bit
- 5/8-11 tap and die OR 5/8-18 tap and die
- Hammer
- Welder (MIG and Spot preferably)
- Grinder
- Something to tell you what 60 degrees is. (I used a piece of paper folded in thirds. See step 15)
- Vice
OPTIONAL:
- Lathe
- Two working vice grips

MATERIALS:
- 40 cm (16 inch) of 5/8th's inside diameter pipe
- 300 cm (10 feet) of 1 inch wide by 3/16th's inch thick band iron

TOOLS:
- Cutting tool (hacksaw, bandsaw, chopsaw... Something to cut with)
- Grinder
- Drill
- 1/4 inch drill bit
- Centre Punch
- Welder (MIG preferably)
- Something to tell you what 60 degrees is. (Bonus step!)


- Cut 2 pieces of 1 inch wide by 3/16th's inch thick band iron at 150cm (5 feet) each.  

- Cut 4 pieces of pipe with (just over) 5/8th's inside diameter at 10 cm (4 inches)

- Measure in 15 cm (6 inches) from the end of the band iron and weld the pipe at 60 degrees (See Pic #2)

- Measure in 26 cm (10.5 inches) and drill a centred 1/4 inch hole (See Pic #3)

- Repeat on both sides of each piece of band iron

MATERIALS:
- 240 cm (8 feet) of 1 inch wide, 3/16th's inch thick band iron

TOOLS:
- Cutting tool (hacksaw, bandsaw, chopsaw... Something to cut with)
- Grinder
- Drill
- 1/4 inch drill bit
- Centre Punch

- Cut 2 pieces of 1 inch wide by 3/16th's inch thick band iron at 120 cm (4 feet)

- Measure in 41 cm (16.5 inch) from each end and drill a centred 1/4 inch hole

- Measure in 50cm  (20 inch) and drill another centred 1/4 inch hole. 

- Grind and round the edges to remove sharp corners

MATERIALS:
- 480cm (16 feet) of 5/8th's rod.

TOOLS:
- Cutting tool (hacksaw, bandsaw, chopsaw... Something to cut with)
- Grinder
- Drill
- 1/4 inch drill bit
- Centre Punch


- Cut the 5/8th's rod into four 120cm (4 feet) lengths.

- Measure 6.25 cm (2.5 inches) from one end and drill a 1/4 inch hole through.  (only on one side, not both.  Each bar should have one hole in it)

- Grind/file the sharp corners to slightly round the ends, and you're done.

MATERIALS:
- 15 cm (6 inch) of 2.5 cm (1 inch) wide band iron that's 3/16th's thick
- 15 cm (6 inch) of 2.5 cm (1 inch) wide steel square bar that's 1.25 cm (.5 inch) thick.
- 30 cm (12 inch) of 5/8th's inside diameter pipe.
- Four 1/4 inch bolts with corresponding nuts that are 1.5 inches long

TOOLS:
- Cutting tool (hacksaw, bandsaw, chopsaw...)
- Welder
- Drill
- 5/8-11 tap and die OR 5/8-18 tap and die
- 17/32's drill bit OR 37/64th's drill bit
- 11/16th's drill bit
- Centre Punch


Axle mounts:

- Cut the thick band iron into two 7.5 cm (3 inch) pieces

- Cut the thin band iron into two 7.5 cm (3 inch) pieces

- Cut the 5/8th's pipe into four 7.5 cm (3 inch) pieces

- Weld the pipe to the thick band iron with the tops touching, making a 60 degree angle between them (see Pic #5)

- Drill a hole that is either 17/32's OR 37/64th's, depending on the tap and die you are using, in the centre between the pipe. (17/32's if using 5/8-11 tap and die, or 37/64th's if using 5/8-18 tap and die)

- Weld the thin band iron to the other side of the pipes, so it lines up with the edges of the thick piece. (See Pic #6)

- Once it is all together, drill through the hole in the thick band iron, and through the thin band iron so that they line up.  (See pic #1)

- Use a 11/16th's drill bit and drill the hole on the thin band iron bigger.

- Thread the hole on the thick band iron with the appropriate tap.

- Now for the tricky part.  You have to cut straight down the centre of the pipe (top to bottom) so it separates into two pieces (See pic #1).  I was lucky, I was able to fit it in the bandsaw and cut straight through like that.  It was easier then hacksaw, but it wasn't perfectly straight, so my cut through is slanted.  It still works though.

- Anyways, now you have two pieces that kind of look like the pieces in Pic #1.   Remember, one piece of thick band iron will match up with one piece of thin band iron, I'm sure its practically impossible to make them perfectly interchangeable.  So, you will need to mark them so you remember what goes with what.  I put three centre punch marks in the centre of mine. (See pic #1 and #4/5)

- To drill the holes, mark 1.25 cm (.5 inch) up on both sides of the half with the thin band iron and centre punch.  (See pic #4)  Then drill a 1/4 inch hole through.  Repeat on both thin pieces (Don't drill holes on the halves with the thick band iron yet.

-  Once you have that, you'll want to proceed and do to step 6 and 7 before continuing.

AFTER STEP 6 AND 7

- Once you have the throwing arm holder and axle and such, you may assemble them together.  Slide the throwing arm holder and ball bearings into the centre of the axle.  Place the spacers on either side of it.  Screw the thick band iron half on either side of the axle.  place the A-frame bars in, with the holes inside the half of the pipe.  Place the thin band iron half on the axle, so it fits around the A-frame bar and line up with the thick band iron piece, and then screw on the axle nuts to hold it together. (See Pic #8)

- Now, I had a friend to help me do this, but I'm sure its possible to do it alone.  Twist the A-frame rod so that the hole in it lines up with the hole in the thin half.  Then, drill a hole through that so that a hole is drilled in the thick band iron half, that lines up perfectly with the other 2 holes.  Now, take your 1/4 bolts and nuts and put them through the holes (See Pic #6).

- Repeat on all the other pipe halves.

- Pic #8 shows how all the A-frame bars fit inside the pipes with the bolts, and shows how to assemble the axle.

- All that is left to do is to attach the safety, but to line it up properly you need to do it at the end once the throwing arm and trigger is complete. So we'll get back to that in step 12.  So far, your pieces should look like mine, except no piece of pipe on the thick band iron, nor on the throwing arm holder.

MATERIALS: 
- 45 cm (18 inch) of 5/8th's rod
- 2.5 cm (1 inch) of 1 inch thick hexagon stock (1 inch from flat side to flat side)
- 25 cm (10 inch) of pipe that can slide over the 5/8th's rod

TOOLS:
- 5/8-11 tap and die OR 5/8-18 tap and die
- Cutting tool (hacksaw, bandsaw, chopsaw.... Something to cut)
- Drill
- 17/32's drill bit OR 37/64th's drill bit
- Centre Punch


- Cut the pipe in half (12.5 cm (5 inch) pieces)

- Thread 7.5 cm (3 inch) on either side of the 5/8th's rod

- Cut the hexagon stock in half (1.25 cm (.5 inch) each)

- Drill hole through the centre of the hexagon pieces (17/32's if using 5/8-11 tap and die, or 37/64th's if using 5/8-18 tap and die)

- Thread the inside of the hexagon pieces to make your nuts.

MATERIALS:
- 40 cm (16 inch) of steel square pipe with a 1 inch square internal diameter
- 2 ball bearings with a 5/8th's hole through them ( must fit on the axle)
- Pipe that the bearings can fit into (I had to wrap a layer of electrical tape around mine to wedge them in).  Cut it to about 1.25 cm (.5 inch) thick, or about the thickness of your bearings.  You need 2 pieces, one for each bearing.

TOOLS:
- Cutting tool (hacksaw, bandsaw, chopsaw...) 
- Welder
- Drill
- 11/16th's drill bit
- 5/8th's drill bit


- Take the square pipe and drill a 5/8th's hole 2.5 cm (1 inch) away from the end. (See Pic #1)

- Drill an 11/16th's hole about 8.5 cm (3 1/4 inch) from the other end.  The distance between the centre of both holes should be 30 cm (12 inch), elsewise it wont be a 5:1 ratio.

- Take the two pieces of pipe, and wedge the ball bearings into them.  Put the axle through one, then slide it through the 11/16th's hole, then put the other bearing on the other side.  Line up the holes and ball bearings so that the axle can slide in and out neatly, and can pivot without grinding on the metal.  The bearings should support it for smooth motion, not the steel. Tack weld (weld quickly, just a small dab) the pipes to the holder, then test to make sure that everything lines up right.  Remove the ball bearings and the axle and weld securely.

- Insert the ball bearings, make sure the axle fits in nicely, and you're good to go! (For now.  Step 12 we'll add the safety.)

The throwing arm is 6 feet long of plywood glued together.  It is a 2.5 cm (1 inch) square.  It was too big to get a picture of all at once, so here are pictures of the important bits.  When I say top, I mean the side with the sling, bottom is the side with the counterweight.

MATERIALS:
- 6 feet of plywood in a 2.5 cm (1 inch) square.
- 1/4 nut and bolt that is 1.5 inches long.
- Four 1/4 inch washers
- Two keyrings
- Wood Screw
- 1.25 cm (.5 inch) of steel square pipe with a 1 inch square internal diameter
- Release pin.  I took a small piece of 1/8th inch welding rod and sharpened the end, but you could use a nail with the head cut off.  It has to be smooth.
- Lots of twine.  I braided mine , but if you have strong stuff you wont need to.  About 10 feet.  More on this later.
- Piece of denim.  I used the legs of an old pair of jeans that I had turned into shorts.
- Needle and thread

TOOLS:
- Drill
- 5/8th's drill bit
- Hammer

Arm:

- If you haven't already, cut your plywood to a 180 cm (6 foot) length.

- Make sure it is 2.5 cm (1 inch) square.  It has to fit snuggly inside the throwing arm holder.

- Insert the arm into the holder, and line it up flush with the bottom.

- Drill a 5/8th's hole through the holes in the holder, and through the wood.  It should look like Pic #3 when removed from the holder. 

- On the top, slide the small piece of throwing arm material over the end.  It should fit snuggly.  

- Hammer the release pin into the top.  The metal around prevents the wood from splitting.  (See Pic #2)

- Take the 1/4 inch bolt and weld a washer vertical on the head, then slide one of the keyrings onto it. (See Pic #4)  Put the other 2 washers on the bolt, and put the nut on so you don't lose it.  Save this for later.


Sling:

- Take your denim and fold it into a rectangle so its two layers thick.  Sew it so it stays together. 

- Cut the corners off, so it looks like... A rectangle with a triangle on either side.  (See Pic #1)

- Sew the corners over the triangles, so its nice and thick on either side.  

- Cut a hole in the centre of each triangle and slide the twine through.  Loop it around itself, and tie a knot, and sew it down, make sure it is securely attached.

- Now, for the length of the twine.  You can read all about how different lengths are better, and I have no idea which is the best.  I dont even know if my length is any good.  But, it works for me.  I cut mine into 6 pieces of about 165 cm (5 feet, 6 inch) and then braided three together so I ended up with two pieces of about 5 feet.  On the end of one, tie on the other keyring so that it can slide on and off the release pin.  On the other, attach it to the end of the throwing arm, just under the metal bit (See Pic #2).  I used a screw and a washer.  So, do your own research, and pick what length works best for you.   Or, do what I did.  On mine, when the ring is on the release pin, and the strings are pulled taut, the sling barely touches the axle when running parallel to the arm.

This pin is used to attach the counterweight to the end of the throwing arm.

MATERIALS:
- 6.25 cm (2.5 inch) 5/8th's rod
- 2.5 cm (1 inch) of 1 inch thick hexagon stock (1 inch from flat side to flat side)

TOOLS:
- 5/8-11 tap and die OR 5/8-18 tap and die
- Cutting tool (hacksaw, bandsaw, chopsaw.... Something to cut)
- Drill or lathe
- 5/8th's drill bit
- 17/32's drill bit OR 37/64th's drill bit
- Welder (MIG preferably)

- Cut hexagon stock in half (1.25 cm (.5 inch) each). 

- Drill a centred 5/8th's hole through one (I used a lathe)

- Slide on to the end of the rod and weld in place, flush with the top.  Weld from the top at a high temperature, don't weld underneath. (See pic # 2)

- On the other side, thread the rod just over .5 inch with 5/8-11 or 5/8-18 die (See pic # 2)

- With the other piece of .5 inch hexagon, drill a 17/32's hole if you used a 5/8-11 die, or a  37/64th's hole if you used the 5/8-18 die.

- Thread the nut with the corresponding tap. (5/8-11 or 5/8-18)

MATERIALS:
- 170 cm (68 inch) of 1 inch wide, 3/16th's inch band iron
- 30 cm (1 foot) of 1 inch thick round stock
- Two 1/4 inch bolts, 2.5 inch's long with nuts
- Eight 1/4 washer's

TOOLS:
- Cutting tool (hacksaw, bandsaw, chopsaw... Something to cut with)
- Grinder
- Drill
- 1/4 inch drill bit
- 5/8th's drill bit
- Centre Punch
- Welder (Spot welder preferably)

Holder's:

- Cut four pieces of 1 inch wide, 3/16th's thick band iron at 25 cm (10 inch)

- Cut four pieces  of 1 inch wide, 3/16th's thick band iron at  17.5 cm (7 inch)

- Weld (I used a spot welder) two of the 25 cm (10 inch) pieces at 90 degrees (See Pic #1) 

- Drill a centred 5/8th's hole where they overlap(See Pic #1)

- Now, for the last two pieces, you can decide where to weld them on.  On mine, the gap between the pieces is a tiny bit over 15 cm ( 6 inch), because my weights are between 1.5 and 2 cm wide, and I like to put eight on.  I designed it with eight 2 cm thick weights, but now some of the bigger weights I use are only 1.5 cm wide, so I can fit 9 on.  Anyways, you pick what kind of weight you want on and measure accordingly. (See Pic #4)

- Decide how far apart you want the 17.5 cm ( 7 inch) pieces to be, and weld them in place

- Drill a centred 1/4 inch hole 1 inch from the base of the 17.5 cm (7 inch) piece. (See Pic #1)

- Grind and round all the sharp corners.

Weight bar:

- Cut 30 cm (1 foot) of 1 inch thick round stock

- Grind to round the corners

- Heres where it gets tricky again.  The holes in the weight bar (1/4 inch holes) have to be far enough apart so that you can get the holder on, and fit all your weight in between it.  For mine, I just drilled one hole, attached the holder, then used a transfer punch so I could see where the next hole should go. Hence why mine is lopsided. 

Assembly:

- Slide your weight on the bar

- Put one holder on one side, push the 1/4 inch bolt through and put two washers between the holder and the weight bar

- Put two more washers on the other side of the weight bar, before you put on the other holder.

- Put on the nut to hold it together.

- Repeat on the other side

So it should be holder, two washers, weight bar, two washers, holder, nut. (If you were looking at if from the front)

MATERIALS:
- 18 gauge sheet metal, two pieces that are 90 cm (3 feet) by 35 cm (14 inch).
- 45 cm (18 inch) of 1 inch wide band iron thats 1/8th inch thick
- 10 cm (4 inch) of angle iron. (Four pieces of 2.5 cm (1 inch) each)
- Two Hinges
- Old pair of vice grips
- Trigger string

TOOLS:
- Welder (MIG)
- Hammer
- Vice
- Sheet metal cutter (must be straight)
- Sheet metal bender


- Take sheet metal, measure in 10 cm (4 inch) from each side (See Pic #1)

- Bend both pieces so that it makes two 90 cm (3 feet) long square U shape's with 90 degree corners.  (See Pic #1)

- Cut angle iron into four 2.5 cm (1 inch) pieces

- Drill a centred hole on one side of each angle iron piece. (See Pic #5)

- Weld two of them to the end of one of the U shaped pieces, flush with the end (See Pic #1 and #4)

- On the opposite side of where you welded the angle iron, weld the hinges to the bottom.  I only used one hinge, but two would be better. Just space them equally instead of centering them. (See Pic #3)

- Line up the other U shape, and weld the hinges to the bottom of that piece as well. The sling will be travelling from the side where the angle iron is flush, along to the end, so make sure there is no lip for it to catch on.  Also, make sure it folds nicely in half.

- Now, you need to assemble the four base pieces (front to back, side to side, steps 2 and 3)

- Line up the angle iron that you have welded with the holes on the side to side pieces. (See Pic #7)

- Bolt it in place with the inch long 1/4 inch bolts.

- Make sure that the base is nice and square, the guide rails help keep it that way so it doesn't squish.  Line up where the next pieces of angle iron (the other two pieces) would go on the other rail, so they line up with the holes on the other side to side pieces. Lots of the second rail will be sticking out of the base. (See Pic #1 on the intro step)

- Take the 45 cm (18 inch) of band iron, and measure just under 15 cm (6 inch) in on either side. 

- Bend those marks at 90 degrees with a vice and hammer (or whatever else you have) so you have a square U.  It should slide over the outside of the sheet metal U. (See Pic #3)

- Now, the rest of the trebuchet needs to be assembled. (See step #13)

- With the vice grips, tighten them until ends are barely touching.  Take the bolt you made from step #8 that I told you to save till later, and make sure that if you put the keyring into the vice grips, you can pull on it and it won't slide out.  Don't make them too tight, you should be able to snap them open with a slight tug on the release lever on the vice grips.

- With your vice grips adjusted, and your steel U of band iron, put the band iron over top the sheet metal so it sits on the outside, and sticks down about 5 cm (2 inch).  From the bottom of the sheet metal, to the cross bar of the band iron should be 20 cm (8 inch).

- Line up your adjusted vice grips so that where the ends meet, is centred over the middle of the sheet metal.  Also, it should be turned parallel to the band iron. (See Pic #6)

- Weld the vice grips in place.

- Heres where you have to line up the trigger.  This is also where magnets, or two extra vice grips would be useful.  The throwing arm should almost touch the end of the guide rail.  (See Pic #1 on the intro step)

- You need to put the bolt from step #8 into the throwing arm, so that it lines up with the vice grips. Obviously, if you put the bolt too close to the axle, it will be too high for the vice grips to reach, and too far towards the end of the arm and it will go right past. (See Pic #8)

- So, using the magnets or vice grips, move the band iron U along the guide rails until you find where it would line up with the throwing arm nicely.  Make sure the distance between the cross beam of band iron and bottom of guide rails is always 20 cm (8 inch).  Once it is lined up, weld the U in place, and drill a hole in the throwing arm and put the bolt in.  Use a washer on each side.

- For the string, you need to attach one end to the release bar of the vice grips.  I just looped it around, so it falls off once in awhile, but hot glue or epoxy or whatever you want could be used to attach it.  Now to shoot it, all you need to do is tug the string, and the vice grips will release, letting the weight fall and the arm swing up! (See Pic #6)

MATERIALS:
- 45 cm (18 inch) of round stock that can fit through your safety pipe.
- 11.25 cm (4.5 inch) of safety pipe.

TOOLS:

- Cutting tool (hacksaw, bandsaw, chopsaw... Something to cut with)
- Welder (MIG preferably)
- Grinder


- Cut the pipe into three 3.75 cm (1.5 inch) pieces

- Assemble the trebuchet (Must have everything else built up until this point. Watch the Assembly video in step 13)

- Weld one piece of pipe to the fat piece of one of the axle holders. (See Pic #2)

- Take the safety bar and put it through, line it up with the other axle holder, and weld another piece of pipe to the other axle holder so the pipe is parallel to the floor and slides in and out.

- Line up the third piece of pipe in the middle between the two, and weld it to the throwing arm holder so all three are in line and the bar slides in and out.  Make sure that the arm sits in the trigger nicely.  (See Pic # 1 and 3)

The easiest way to do this, is watch the videos.  Its in 2 parts, about 15 minutes total.  I've also included some pics of key points.

Here is the launch video, on how to set it up and fire! Good luck and thanks for reading my Instructable!

UPDATE: Yes, the throwing arm broke, but that's because I was overloading it.  And the arm is old. So, don't use more then 30 pounds as a counterweight unless you have a stronger arm!

Seeing as this project uses equilateral triangles, I needed to know what 60 degrees was more times then not.  So, I devised a method to make 60 degrees out of a sheet of paper.  

MATERIALS: 

- Paper

TOOLS:

- Your hands


(You could probably do this by following the pictures.  Heres the steps anyways)

-  Fold paper hamburger style. 

- Fold paper again into quarters to find the centre, and unfold.

-  Fold from the centre to the edge upwards on an angle, approximately a third of the way

-  Fold the other side up in the same way, lining it up with the first crease.

-  The edge of the first fold should line up with the crease from the second, and the edge of the second should line up with the crease from the first.

-  Once it does, you have 60 degrees!

I used this when I was lining up the pipe in step 2, to make sure it was 60 degrees between the pipe and bar, and also in step 5 to make sure those pipes were at 60 degrees as well.