Things You’ll Need

The usual suspects

4d finish nails

Brace drill

5/16” bit

Screwdriver and 1 ¼”drywall screws

(2) 7/16” wrenches

(4) ¼” x 4 ½”” hex headbolts

(1) ¼” x 3” hex head bolt

(10) ¼” flat washers

(1) Door knob stopper

(1) Towel hook (with twohooks)

(2) Rubber bands 3 ½” x ½’

(4) ¼” lock nuts

(1) ¼” wing nut

Block plane

Safety glasses

Lesson 19

Marshmallow Catapult

Here’s a project that you can build and use to learn about engineeringterms such as force, trajectory, tension, and of course the theory that oncean object is in motion it tends to stay in motion. Oh who am I kidding,here’s a cool project to build so you can launch marshmallows into theair like scud missiles!

Again, like some other projects in this book, there are not a lot of parts toput together but things have to be done in order. Particularly, all theholes have to be drilled precisely where shown in the diagrams in orderfor the catapult to work properly. Remember, measure twice cut once(and drill once).

Here’s the cut list for our project:

Handle: (1) ¾” x 1” x 7”

Side panels: (2) ¾” x 5 ½” x 6 ½”

Long boards: (2) ¾” x 1 ½” x 14 ½”

Catapult arm: (1) ¾” x 1” x 10 ½”

Tall spacer: (1) ¾” x 1 ½” x 5 ½”

Short spacer: (1) ¾” x ¾” x 4”

We pieced our catapult together with woodscraps left over from other projects and you canprobably do the same. If you do need to buy

lumber, the side panels can be cut from a 1 x 6 x 14” board, and all therest can come from a 1 x 2 x 4’ board. Remember that a 1 x 2” is actually¾” x 1 ½” so you won’t have to rip to width any pieces except thehandle, catapult arm, and short spacer.

Even if you have all the wood left over from other projects a trip, to thehardware store is going to be necessary (don’t you just hate that). The listof things you may need is listed in the “Things You’ll Need” section atthe beginning of the lesson.

Long boards

Side panels

Catapult arm

Tall spacer

Short spacer

Handle

Catapult parts cut to size

Hardware for catapult

Step 1Let’s work on the handlefirst. If you haven’t cut itto size from the cut list yetgo on and do that. Nextwe need to cut a notch intothe bottom section of thehandle. This is so we canuse the handle to hold thecatapult arm in placebefore firing. Use yourcombination square and set it to read at ½”. Then, use your pencil toslide along with the combination square to mark off 3 ¼” on the side thatmeasures 1” in width. We need to angle the top of the notch so that itbetter grips the catapult arm. So, instead of cutting straight across, dropdown about a ½” and cut at an angle back up to your cut line. (See thepicture of the catapult parts cut to size).

Step 2We need to glue the short spacer to the two long boards next. Thespacer’s job is to, you guessed it; keep a space between the two longboards. If we didn’t have a spacer blockthe two long pieces would pinch togethertrapping the catapult arm. Take one of thelong boards and measure over 1 1/8”. Atthis mark place the short spacer flush withthe bottom edge and trace an outline ontothe long board. Next spread some glue onboth sides of the spacer and line it back uponto the long board and place the otherlong board on top. Use your speed squareto make sure that the ends of the longboards are even. Using some help to makesure that the pieces don’t slide around puta couple of 4d finish nails into each side tosecure the pieces until the glue dries.

Step 3Next, let’s lay out the holes in theside panels. First thing to do is toplace an arrow pointing along thelength of each side panel. The twopanels need to be mirror images ofeach other so one panel the arrowpoints to the left, the other panel itpoints to the right. These arrowswill point towards the small spacer and also the side with the arrowswill be the outside of the panel. This will help avoid drilling the holes inthe wrong spot and from connecting the panels backwards. With thearrows facing up take both side panels and lay out the lines and markthe placement of the holes with your measuring tape and speed squareaccording to fig 1. Pay close attention to which way the arrow ispointing for each panel.

½” 1” 1” 1” 2 ¼” ¾”

¾”

¾”

2 5/8” 3 1/8” ¾”

Fig. 1 Lay out for right side panel, left side laid out just the opposite

The other side panel is a mirror image, so to lay it out flip all themeasurements around. The arrow will also be pointing in the oppositedirection. It’s easier to lay out the holes on one side panel and then place thepanels back to back (both arrows on the outside and facing the samedirection) and drill both pieces at the same time. This way the holes line upand it avoids confusion (if you ’re not already confused).

Step 4The hex head bolts that we’reusing are ¼” size but to makethings a little easier whenputting things together use a5/16” drill bit in your bracedrill. In some places you willbe putting the bolt throughthree different holes before youget to the other side and theextra room will help in locatingthese holes. Drill the holes forboth side panels. You can evendrill both side panels at the same time by putting them back to back inthe vise. If you do this pay attention to the arrows, they should both beon the outside and pointing in the same direction. Also, make sure youhold the drill level. If you don’t and you angle the bit a little the twoholes won’t line up and the bolt may not go through both holes. Have afriend watch the drill as you turn it to make sure things look straight.

Step 4After the holes have beendrilled in both side panels weneed to attach them to thelong boards. The arrows faceout and towards the shortspacer we installed earlier.Insert the tall spacer betweenthe two long boards just forsupport at this time. Nowwith the side panel flush withthe bottom edge place a screw

in the end of the long boards about ¾” up and ¾” over from the bottomof the front edge (see picture). With both side panels attached with onescrew each let’s drill the holes through the tall spacer.

Clamp the pieces down to the workbenchand with the same 5/16” bit in your drillplace the bit in the hole that’s at thebottom corner of the side panel. We needto finish drilling the hole all the waythrough the long board, the tall spacer andfinally through the other long board onthe other side. Your bit may not be longenough to go through all this and even if itis it’s best to only go halfway througheach side and then flip the piece over andcontinue the hole until they both meet.This way, if you start to get off squarewith your bit as you drill, you won’t carrythe angle all the way through to the otherside and miss the hole that you’ve allready drilled.

Drill the top corner hole the rest of the way through the tall spacer just asyou did with the bottom hole. Take a bolt and test your fit with bothholes. If you have trouble getting the bolts to go all the way through theholes they may need some friendly persuading with your hammer. Isaid friendly persuading. If you have to hit the bolt hard and it’s still notgoing through, remove it and see if you can tell where it’s getting stuck.You may have to use sandpaper, or if things are way off, a bigger drill bitto allow the bolt to go through.

Now, drill the hole that’s at thebottom towards the middle of theside panel the rest of the waythrough the long boards just aswe did for the other holes. Thisis the hole that the catapult armwill pivot on, but we need to waitto drill that hole through the arm.That step is coming up.

Here is how to install the bolts: Take a bolt and slide a washer on, insertthe bolt through the holes, place another washer on the end and finallythe lock nuts are tightened. Follow this procedure and install the twobolts that go through the tall spacer.

Before you tighten the nuts, placeyour speed square against the side ofthe panels to make sure they aresquare. If you tighten the nuts toomuch you can pull the side panelsout of square. One of the reasons forusing lock nuts is you don’t have totighten them down in order to keepthem from loosening up, where everyou stop turning them that’s wherethey’ll stay.

Step 5Grab the doorknob stopper, the towel hook, and the catapult arm andhead to the workbench. (Is it just me or does that just sound plainweird?) The door knob stopper (let’s shorten that to DKS) that webought had a sticky backing but we didn’t trust that to hold it to thecatapult arm so we screwed it to the arm with a 1 ¼” drywall screw onthe side that’s ¾” in width. Make sure you leave ½” space above theDKS for the handle to have something to grab onto. Just below the DKSplace the towel hook with the hooks pointing up towards the DKS. Wefound out after we installed our catapult arm that it rubbed the inside ofthe long boards as it moved. To prevent this we used some sandpaper toremove some material so that it wouldn’t stick.

On the opposite end we need to drill the hole for the catapult arm topivot on. Use fig. 2 for the placement of the hole.

¾”

½”1”

Catapult arm

To make sure that the corner of thecatapult arm doesn’t hit the surfaceit’s sitting on as it swings forward; wechamfered the edge using our blockplane.

Before we secure the catapult arm with a bolt we need to drill one lasthole.

Fig. 2

Step 6We need to drill a hole through the end of the long boards and throughthe handle. Figure 3 shows the placement of the hole in the long boardsand the handle. Drill the hole for the handle separate from the holesthrough the long boards. Because the bottom of the handle is notched tohelp catch the catapult arm there’s not much room for error in drillingthis hole, so pay careful attention to place the drill bit in the center of thewood.

½”

¾”

Long board

5/8”

¼”

Handle

Now we can assemble the handle and the catapult arm. Just as we didbefore, slide a washer over the bolt, insert the bolt then place anotherwasher on the end of the bolt, and finally the lock nut. The catapult armuses a 4 ½” bolt and the handle uses the 3” bolt. The catapult arm needsto be able to move freely so just tighten the lock nut enough so that thebolt doesn’t move.

Fig. 3

Trajectory- Thecurved path of anobject as it moves fromone point to another.

Step 7There’s one more bolt that you should haveleft. This bolt will go through one of the fourempty holes that are on the top of the sidepanels. This bolt will stop the catapult armat different points along its arc dependingupon which one of the holes the bolt is in.Changing the stopping point will change thetrajectory of the marshmallow. The holeclosest to the handle will give a highertrajectory, while the last hole furthest fromthe handle will give a lower, straighter

trajectory. Secure the bolt with awasher on each end but this timeinstead of a lock nut use a wingnut. The wing nut will makemoving the bolt into differentholes easier.

Step 8There’s one last thing to do in the construction of the catapult. Usingyour brace and a 1/8” diameter bit drill a small pilot hole 1 ½” deep thatgoes through the catapult arm nearthe top close to where the handle is.The exact placement of the holedoesn’t matter just make sure that itgoes through the long board andinto the catapult arm. Next, put a 4dnail in the hole to act like a safetypin. With this pin installed, thecatapult arm will be unable to move.

Step 9Let’s get this thing ready to launch! First thing we need to do is to wrapa rubber band around the bolt on each side of the tall spacer. Afterwrapping a rubber band around the bolt loop one end back through thecenter and pull it tight. (Yeah, that last sentence would make muchsense to me either if I hadn’t written it; look at the picture for moredetail.) Do this for both rubber bands. Next bring the catapult arm upand slip the rubber bands around the hooks. Slowly pull the arm downand put the safety pin in. Place the marshmallow into the cup then movethe handle over the catapult arm and pull out the safety pin.

Make sure that nothing and especially NOBODY is around or in front ofthe catapult.

5, 4, 3, 2, 1, release the handle and fire away!

Safety pin

Caution! This catapult should not be used to throw anything except large size marshmallows.Keep hands clear of the catapult arm when being released. Make sure the area is clear before usingthe catapult of people, pets or breakable objects (we don’t want Mom and Dad mad at us, do we)? If,after repeated use the catapult arm becomes badly dented from hitting the stopper bolt, discontinueuse. You can easily replace the dented catapult arm with a new one. Anytime the catapult arm ispulled down with rubber bands attached you should have the safety pin in. The only time it is safe toremove the safety pin is after the handle is underneath the catapult arm and you are ready to fire.

Failure to follow these safety procedures may result in serious harm. The author assumes no liabilityfor harm resulting from the use of the catapult.

(1) Wrap a rubber band around the bolt on each side of the tall spacer.(2) Take one end of the rubber band and pull it back through the loop.

(3) Bring the arm up and loop the rubber bands around the hooks.(4) Pull the arm down and insert the safety pin.

(5) Raise the handle until it catches the arm, pull the safety pin out andload the marshmallow into the cup.(6) Pull back on the handle and FIRE!

5 6

1 2

3 4