Introduction: Rocket Racers Activity


Rocket Racers is a very fun activity that is designed for camps but can be done anywhere you choose. The basic premise is that campers build small cars that they then race against each other (safely) using model rocket engines.

This has many advantages over traditional model rockets such as:
1) It can be done inside or outside and isn't weather dependent
2) The whole activity is self contained so it can be done in a designated area (unlike rockets which can go everywhere)
3) It's more fun because campers are racing each other instead of just launching.
4) It's faster to set up
5) In my completely biased opinion, it's a lot cooler (this has been confirmed by campers and random staff walking by)

This Instructable shows how to make the Track that the cars race on, the Launching mechanism, the scoring Flags, and the pieces for the Racers as well as how the campers will put them together.

The Track is fairly simple, as is the Launching mechanism (based on a model rocket engine one modified to launch two engines at once). The scoring Flags were a bit difficult to come up with (if you want to make your own) but not very hard to make with instructions. The Racers are designed to be as easy as possible to make in bulk and very simple to assemble.

Lastly is how the entire system of the activity runs as well as safety instructions and concerns along with a bonus Engine Award mini-Instructable. 

Step 1: Tools and Materials

- Drill with drill bits
- Screw driver
- Saw (handsaw will work but a miter saw, especially a power miter saw, will make the work go faster and more precisely)
- Something to cut PVC with
- Soldering iron w/ solder
- Safety equipment (goggles, mask, etc. You'll also need goggles for the actual racing)

Track (open to suggestion; look at pictures in step)
- 4x 1" x 10" x 6' board
- 5x 2 x 4
- sheet metal
- plexi-glass
- 24' 1/8" wire rope cut into two 12 foot pieces
- screws
- something to use as shock absorbers. I used very dense styrofoam but tennis balls will also work (one cut in half is fine)
- strong tape (i recommend/used Gorilla tape, duct tapes stronger cousin)

- 3/4 inch thick scrap wood; enough to make a box around 12x5x5 inches
- hinges
- three switches (if you can, make one a key turning kind. It looks awesome). The best choice (To see why, see Step 7) would be momentary NO (normally open, i.e. off) switches/buttons
- wire
- 4x AA battery pack
- 4x alligator clips
- solder/soldering iron

- Scrap 2x4 (I actually used a 2x3 stud)
- Lego plate/axle pieces (used to make a smoother turn/slide instead of rubbing against the wood itself)
- Scrap 1/4" thick wood
- Rubber bands

Cars (each)
- 6" x 3.5" x 1/4" board
- 4x wheels w/ axles
- 3.25" length of 1" diameter PVC
- 1.5" eyebolt w/ nut (the shaft should be 1.5", not the whole bolt)
- Whatever you want to use to decorate the car with

Step 2: Track

Unfortunately, I did not take pictures while I was making this. I took a bunch afterwards, though, and looking through them should give you a  good indication of what to do. 

The boards used might be wider than the track itself but this lip won't get in the way and you can just ignore it. If you want it to look nicer, you can use narrower wood (as I should have) or cut it but DON'T just make the car tracks wider. This will allow the cars to swerve to the point where the friction from them pressing against the walls will stop them.

Now the actual building. Because the track would be too heavy/unwieldy as one object, it is split into two parts, front and back. They start out the same.
Screw the 2x4s into the boards edgewise (with the "2" inch part in contact with the boards) in the following way. One 2x4 is flush with the edge of the board, and the other two are spaced so that they make two parallel tracks, each 6.5 inches wide. The 2x4s might be longer than the boards so just cut off the extra from the second half of the track. You might even be able to buy one less board because of all the extra. Incidentally, the overlap on the first half actually makes it easier to carry because it gives you something to grip. Adding handles on the sides would also not be a bad idea.
The next step for both halves is to screw in an end piece to one end of the board. The piece should be a 2x4 and also be placed with the "2" inch side touching the board and should fit snugly in between the two tracks. As there are two halves of the track with two tracks each, you'll need four such pieces.
Here's where the two halves differ.

First half:
1) Cover the part of the end piece that is facing the track in sheet metal. This piece will repeatedly have rockets shot off of it and the metal will protect the wood from the flame. Use screws to keep it there.
2) Now cover the first 2-4 feet of track with a layer of plexi-glass. This isn't entirely necessary, as I found out, but it's not a bad idea to have something protecting you for the first couple of feet of track from the flame. Because the flame's diameter is very nerrow, you don't have to worry about getting soot on it, assuming the rockets don't get stuck. If you want, you can cover the whole track in plexi-glass. Two notes on this:
1) Don't screw the plexi-glass in too much. It will crack. (I did this.)
2) Don't store the track with the plexi-glass facing outwards, especially in a gym and especially in a gym that campers are playing in all day. A ball will hit it and it will crack. (I did this as well.)
3) Now you need an anchor for the wire rope (to be explained later). You will be using a screw that will need to go to a height equal to the height of the eye-bolt of the car when it is in the track. Make a car (Step 5) and measure. The best way to do it is to either use really long screws or to screw a piece of scrap wood in first, then another screw partially in to get to the right height. A faster way to to screw in the screw at an angle into the end piece, although this is much harder, especially with the sheet metal in the way, and won't work as nicely (I did this).
4) If you want, drill a hole in each of the sides of the track for the clips from the launcher (Step 3) to fit through. If you're going to be removing them, make sure the hole is big enough for the wire AND the clip.

Second half:
1) Just like you did with the first half, put vertical 2x4 blockers at the end.
2) Now take your styrofoam or whatever you're using as a shock protector and attach it in front of the blockers. I put in a screw sticking out of the wood and just poked the styrofoam over it.
Fun bonus: don't include a shock protector so the cars just smash into the wood. Awesome.
With that in mind, know that whatever you use will probably not work perfectly so it's not a bad idea to set up a secondary contest to see who can lose the most wheels. The highest I saw was 3 in one race.
3) Now you're going to put in another screw for the other end of the wire rope. I cut my rope too long and didn't want to waste time cutting it again so I put in a screw at the end, looped the wire rope over and put in the screw to hold it on the side. Be smart and just measure right the first time, keeping in mind the steps you are about to take which will require extra (and don't trust the store person to do it correctly if you're not there. They might try to be nice and give a bit extra). Worst comes to worst, you'll unravel a bit more (see steps) or cut it at home. The screw should stick out of the blocker about 1/4 of an inch, just so the wire can loop over.

Wire rope
Turns out you can't use the normal wire rope holdy things (See picture 10) because they're too big to fit through the eyebolts so due to necessity, I found a better/cheaper way.
At either end of the rope:
1) Unravel the rope about 2 inches. Don't get poked by it.
2) Using the V made by the unraveling, loop it over the normal part of the rope and re-ravel it so it makes a little slip knot.
3) Cover the connection (not the loop, the re-ravels) with a thick, preferably Gorilla, tape. This is to both keep the loop secure and prevent you from getting poked. Tetanus isn't fun. You now have a rop with a loop at the end.
This is plenty secure for what you will be doing, but don't use this in a situation where there will be a lot of pressure on the rope.

Step 3: Launching Mechanism

The pieces you will be cutting out of the 3/4 inch wood are:
2 x 5x12 - Top/Bottom
2 x 4x5 - Left/Right Side
2 x 10.5x4 - Back/Front
1 x kill switch cover (see that step)
(You can adjust any of these if you want but this is a nice size both for putting all the circuitry in and to use.)

1) In the Top piece, you will cut two rectangular holes for the switches that I cut using a scroll saw. They can go pretty much anywhere but they look nice placed about 3 inches from each side and 2.5 inches from the front/back. I also have a circular hole in the front that I use to keep it shut with a short bolt. I like this "latch" because it's easy to take off with a screw driver but since most people don't carry one around, the box stays shut.
The holes are ~1 inch x ~0.5 inches. Just make them the size of your switches so they fit as snugly as possible.

2) The Back has 11 holes, as follows:
a) 4 small (1/8") holes for the leads to come out. Put them in, spaced in pairs on the two ends of the piece. Having them like this will help you later when you only want to take one side's leads for each car.
b) 4 holes for the hinge for the Top. Do these later when you attach the Top.
c) 2 holes for the hinge for the kill switch. Do these later as well.
d) 1 big ol' hole for the kill switch. Place in the center the same way you did with the two switches in the Top

Attaching the whole thing together
Line up all the pieces and screw them together. This includes the Top/hinge.
For the kill switch cover:
1) Cut a piece of 3/4 inch wood that's about 1/2 inch longer in every direction
2) You're going to need to remove wood in the wood so that the piece can lie flat against the Back with the switch's handle (what you flip) protruding either on the ON or OFF position. I used a Dremel with a cutting/shaping bit but a sanding bit or chisel with a bit of patience will work as well.
If you have none of these, you will need to make a small box to cover the switch. I recommend 1/8 inch wood or less and hot glue to hold it together.
3) Chisel (or Dremel) a groove in the Back so that the hinge is flush with the surface when closed.
4) Screw the hinged cover to the back over the hole you cut for the kill switch.
5) To make the cover normally stay closed, you have two options: gravity or elastics. Gravity is easier and only entails putting the hinge on the top of the cover so gravity automatically shuts it. Elastics is a bit trickier with not a lot of added benefits, so I recommend against it. However, as my decision showed, there will be gluttons for punishment who insist. So:
 a) Find a piece of elastic. Rubber bands will work but they will rub against the wood and eventually will wear down. I used elastic string.
 b) Drill 2 holes in the Back right near the hinged side of the cover. The holes should be bigger than the diameter of the elastic.
 c) Thread the elastic through, going over the cover to pull it closed to the Back and attach the ends to the inside of the main box. Look to the pictures for guidance. It's not as complicated as it sounds. I promise.

The circuit diagram is given in the pictures. The idea is that three switches (Racer 1, Racer 2, and Kill) are in series (in any order) with the batteries and the ends connect to two leads each, so each wire splits into 2 with one of each going to the cars.
In other words:
Node 1 >> Switch 1 >> Switch 2 >> Kill Switch >> Batteries >> Node 2
Node 1a and Node 2a go to Racer a
Node 1b and Node 2b go to Racer b

All the wires just need to be long enough that they reach their destinations with enough room that you have enough room to solder and the Top is able to open without ripping out wires. The leads should be very long, in the 3-4 foot range.

Attach and test these circuits using lights or a pair of voltmeters instead of engines. Once you're sure they work, solder everything and glue them in place. Thread the four leads out their respective holes (Remember: one from each node) and attach the alligator clips.

In case you're wondering, yes. It is really fun to pretend you're in charge of a missile silo and are launching nukes when you flip the switches. Enjoy.

Step 4: Flags

My flags were originally made out of a combination of wood and Lego pieces with shock styrofoam shock absorbers to protect the cars. I put the absorbers on in a bad way so they ended up breaking the flags pretty bad in a test run. Turns out the campers didn't care much who won, which was good because one launcher kept firing a moment before the other one. Who knew that fire could be so distracting?
If you want to make them anyway, here's a general idea how:
(Note: In the picture, all flag part names being referred to are in UPPERCASE and in the right hand side flag)
The way the flags work is that each one is always being pulled into the raised position by the RUBBER BAND. At any given point, there is one (or less frequently, two) things preventing it. The primary one is the TRIGGER. It hold the long end of the flag (or FLAG-LONG) until the car hits the its other side and it releases the flag. This is how each flag is raised. However, we don't want both flags to go up if only one car wins, so...
There is also the short end of the flag, or FLAG-SHORT. This side starts out up and when the flag is released, drops down to block the other flag's FLAG-SHORT from moving.
Each flag is built into a BASE. They can be in the same base but putting them in different ones will help you adjust the distance so everything fits.

Rubber band: This part will be trickier than you might expect. The rubber band needs to be strong enough that the flag will snap up to attention as soon as it can, but not so strong that it snaps anything or breaks off pieces. Experiment.
Short end of flag: This needs to be just slightly shorter than the distance to the other flag so it can get in easily, even if the other flag was just released a moment later and the distance has shrunk bit. The kerf of your saw should take off enough and you can always shave off more later if you want. Also, round the corner that will be the part to hit the other flag first (in the picture, is the bottom left corner on the flag on the right). If this corner is not rounded, it will get caught on the other flag and won't go down all the way.
Trigger: Really more about the other side of the trigger. Put a piece of foam there so the car doesn't shatter (unless you want it to, which is pretty cool to watch).
Materials: I made mine out of Lego, which didn't hold up very well. I would recommend plastic (maybe cut with a CNC/milling machine if you have access) or Lego but glued together for stability.

Step 5: Racers - Part 1

The racers are, naturally, the simplest things to make. I was doing this project with 4th/5th graders, who didn't have too much trouble. If your kids are finding it too easy or you want to take up more time after decorating, you can add extras. These are additions to the racers that the kids come up with one their own, things like fins or noses. Just make sure nothing is in back OR IN FRONT of the barrel that holds the engine. The back is shooting fire so anything there will be incinerated (cool) but ill also catch fire and possibly catch other things on fire (not cool). In front of the barrel is mostly safe, though. Just avoid putting things directly in front. The racers are going to be in two parts. Part 1 is what you do as prep for the racers. Part 2 is what the kids do.

The prep is as follows. Each car needs on set of these:

{ x) Do this - Picture y }
1) Cut the board to 6" and drill a 1/8" hole in middle of board, width-wise, and 2.5" from one end, length-wise. - 1
2) Cut the PVC to 3.25" lengths and drill another 1/8" hole 2.5" from the end. - 2
3) Put together the rest of the pieces: 4 wheels and axles along with an eyebolt w/ nut. - 3 + 4 + 5

Putting all these in a bag is not a bad idea.

Step 6: Racers - Part 2

For this part, you'll want to find a balance between instruction and freedom. You don't want to do the project for them, but at the same time, you want them to have a working project. My recommendation would be to read this great article on, especially numbers 1 and 5. 

This is the order that used. Feel free to change it, or even let the kids choose.

0) Put all the axles into their wheels so the next steps easier.
1) One at a time, put a bit of hot glue on the long sides of the board, towards the ends. See Picture 2.
2) Put the axle against the board at an angle (Picture 3) and tilt it into the glue (Picture 4). This will help get a good connection. Make sure the wheel is not pressed against the board tightly. You want it to be able to move freely.
3) Put some glue on top for added stability (Picture 5).
Repeat steps 1-3 for the other three wheels.
4) Put the bolt through the PVC and then through the board. the end of the PVC should line up with the end of the board. See Picture 6. Put a nut on the end and hand tighten (Picture 7).
5) DECORATE! I didn't do much. make sure the kids do. They might be somewhat reluctant, especially boys, but it will make them become more involved/connected to the project. Also do the extras now if you want.

Step 7: Launching Procedure

0) If you want, prepare a bunch of rocket engines before starting the races so you don't lose time. The igniters work on electricity so there's no added danger.
1) Assemble the track, meaning lining up the two halves and attaching the wire rope guides. Place the launcher as far as you can from the track so that the leads still reach. The two campers racing are with you. The rest are farther back unless you have enough safety goggles for all of them.
2) Take both cars and put them in the track, PVC facing backwards, and attach them to the wire rope guides.
2.5) At this point, you and both people launching should put on safety goggles which should remain on until you remove the cars/the smoke clears.
3) If you haven't already, prepare two engines and put them in the PVC and connect the leads from the launcher. Make sure to connect one lead from each pair to the engines.
4) "Close" the track by covering the beginning part with the cover.
4.5) Remind launchers (and yourself) to start holding their breaths when you get to zero, (or "Fire!", if you prefer) in the countdown as there is a fair bit of smoke (from the engines, not the wood burning). Also tell them to flip the switches at zero.
5) Count down from 3. At two or one, flip your kill switch.
5.5) The rockets will fire 2-3 seconds after that. Remember, parallel circuits mean less current so it takes a little longer than normal rockets.

The rockets will fire for a bit after they hit the end of the track. After that, the back of the engine will be hot, as well as some of the metal bits. Be careful and don't let the campers touch anything until you get to it.
5.999...) IMPORTANT: Flip all switches to "off" at this point. Otherwise you may forget and connect the next engines to the leads while they are live. I did this by accident and fortunately got my hands out of the way before the engine fired so I was fine, but to avoid my stupidity REMEMBER THIS STEP. In hindsight, the smart thing would be to get momentary switches for all three. 
6) Unhook the cars from the wire rope from the other side and remove the engines and mark with the name of the car or camper for later when you make the trophies.

Step 8: Engine Awards

As with the scoring, I was surprised that the campers didn't want trophies more and I ended up skipping it. Regardless, here is what's needed:
- Scrap wood (2x4-ish)
- Screws
- Used engines (Try to keep track of the engines so campers can get the engine that they used)
- Paint, if you want

Cut pieces of wood to squares (if you're using a 2x4, that would be 3.5 x 3.5*) and screw in a screw in the center. Screw on the engines with a little glue if they're loose. You can decorate/have the campers decorate the trophies or just put the names of the camper/cars on them. Go nuts.

* The measurements of thickness and width (I am defining length as the long one. 2x4's are typically 8 feet long) are what are known as nominal values. The actual values are .5 inches less. A 2x4 is actually 1.5" x 3.5" x 8 feet.

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