Pinewood Derby Race

Here in the Netherlands we don't really know the Pinewood Derby. I thought it would be fun to do an annual Dutch version.

To make this happen, I need to translate the American dimensions and rules into something that would work for us. The first problem was getting the wheels.

I solved this problem with lots of hours of 3D-printing.

The race was a big succes and all the kids left with ideas on how they are going to do it better next year.

This ended up not being a real step by step instructable, but more a how to, on how I did it. I did include all 3D files, from wheel, track to trophy.

The track

Materials

• 4 mm plywood
• aluminum L-profile
• Wood glue
• Contact cement
• Nuts and bolts
• Nails

Tools

• Saw
• Clamps
• 3D-printer
• Drill

Finish

Materials

• Ply
• Aluminum profile
• Hinge

Electronics

• Arduino
• 3 2-color LEDs
• 3 white LEDs
• 3 light sensitive resistors
• a momentary switch
• a microswitch
• a display
• 3 10K resistors
• lots of wire

Tools

• Soldering stuff
• Computer with Arduino IDE
• 3D-printer

Before I can build a track, I have to decide on the dimensions that will work for us. I want to stay close to the American original, but use materials that are available at my local store.

So for the car we are going to use basic and cheap 44 x 33 mm pinewood. This makes the car:

44 x 33 x 175 mm

For the track I am using 4 mm light ply. (the light ply is both light in weight and color, and I really like how it looks)

One track part will be 122 cm long and 30 cm wide for a 3 lane track. I want a 10 meter track, so I will need 9 track-parts. (122 x 61 is the standard size)

Six track-parts will be straight and simple. Three parts are special:

• The start
• The curve
• The finish

The lanes to guide the cars will be also 4 mm thick and 45 mm wide. With the design of the wheels I made, this will be a nice width to guide the cars to the finish.

Making the 6 straight track-parts is very easy. To make it even easier for myself, I had the plywood precut from the store, so that gave me (for all the tracks):

• 9 parts of 122 x 30 cm plywood
• 27 parts of 122 x 4,5 cm plywood

To make het even easier, I made some templates from 55 mm wide and some 27,5 mm wide. I also prepared some weights.

I want the guide tracks to overlap the next track-part so I extended them a track width (45 mm) forward.

To build 1 track-part you will need:

• 1 122 x 30 cm part of plywood
• 3 122 x 4,5 cm strips of plywood
• 2 clamps
• 2 27,5 mm templates
• 4 55 mm templates
• 1 extra 45 mm wide part as a template
• 9 weights
• woodglue
• 2 20 x 5 mm aluminum L-profiles that are 15 cm long (I used J-profiles)
• contact cement

Start building:

• Clamp the 27,5 mm templates on the edge of the 30 cm plywood
• Glue the 4,5 cm strip on the track, using the clamped templates and the extra 4,5 cm part as a guide
• Put two 55 mm templates next to it.
• Glue on the second strip.
• Repeat for the third.
• Weigh it all down and wait for it to dry.
• Glue the L-profiles on the bottom of the track on the side where the strips are extending. It is wise to make the profiles extend just a little more than the strips (I didn't do this)

Repeat this 8 times. The start and the finish part will be essentially the same, only the start part won't have the aluminum L-profiles on them.

Decide where you want your cars to start. You will need enough track above the start to put the cars. So for me that is at least 175 mm. Cut a slit in the middle of the 3 tracks starting (at least) 175 mm from the edge of the track. Make the slit 1 cm wide and 6 cm long.

Now it was time for me to make some use of my 3D-printer. I printed 5 parts for het starting system. These parts are also easily to make from wood, but I have a 3D-printer, so I might as well use it.

All added 3D-files are 123D-Design files. You can download this program for free and edit the files if you want.

For the starting system you will need:

• 3 L-shaped starting booms (3D printed)
• 1 Block to put the start-button on (3D printed)
• 1 Start button (3D printed)
• 3 Aluminum L-profiles
• 2 Pull-springs
• Nuts and bolds
• Threaded rod
• Contact cement

Print the parts and glue and bold it all in place like you see on the pictures. I had to vile some material off the startbutton, to make it work.

I also glued a L-profile on the length of the bottom to make it easy to use a table as a stand for the track.

To make the curved track-part, we need to bend some wood. We take the only part we have left that isn't used yet. I carefully bended it in-between my hallway walls and left it there for a week. I did the same with the strips, but I used one extra, because one broke in the proces.

After a week I could glue on the strips. I used a strap to keep the track curved while gluing. Instead of the weights, I used lots of clamps.

Because the strips have the inner corner, the part that is sticking out, is slightly to long now, so you will have to cut this extra few mm off.

The strips glued to the track will make sure the track holds shape.

My finish is build out of 2 systems. System one is the two color LEDs that show immediately when a car crosses the line in what place he finished. The LED colors green when you are first, doesn't go on when you're second and goes red when you're last.

The second (more complicated) system shows your time on a display on the back of the finish.

I didn't make pictures or diagrams of how I build it, so all I can do here is explain the idea and share the code.

I use an Arduino nano to do all the hard work.

For the actual sensing of the cars I used 3 light sensing resistors in the 3 lanes. They are connected to the analog pins of the Arduino. They all have a 10k pull down resistor to GND. Three white LEDs in the bridge above them make sure they have enough light to "see" the cars.

On the front, the bridge has 3 LEDs, one above each lane that can light up in red or green. Each is connected (with a resistor) to two digital pins on the Arduino.

I also added a button to be able to reset the system. (I added a LED in the button, just for fun)

With just these components the finish will work.

Display

To make it more fun, I added a display in the back of the bridge.

I used a very cheap OLED display that I still had left over from my watch project. I couldn't get it to work then and it took me forever to get it to work now. I would advise you to use an other display and change the code accordingly. I marked in the code where the code for this display is.

To register the time, you also need the starttime, so I pulled a cable from the startbutton at het start to the reset button in the bridge. So now the system is reset when the cars are started.

Bridge

For the actual building of the bridge, I also printed 4 parts on my 3D printer. I added the files. The connection from the bridge to the track could be a bit better, but I wanted it all to be detachable. For this same reason I used plugs to connect the cable at the start and the finish.

To set up the track, you simply slide the track-parts into each other. For the vertical part I used a wood-clamp that I can attach to a table, chair or something else.

I don't have a 10 meter long room so the first time I fully builded the track was on the day of the race.

At raceday we noticed that the curved track part easily came lose and the start was a bit bobbly.

The easiest way to solve this was to keep the kids away from the track, but what is the fun in that, so for next year I did some little upgrades, that I should have done before the race.

Connect the parts

To make sure that the track stays together during a race, I drilled some holes in the side of the aluminum L-profile at the end of the track-parts. Next I put the track together and drilled the hole trough the wood of the next track-part. When I now stick a nail in this hole, the track parts can't be separated.

Extra clamp

On the back of the start part, I added an extra L-profile and an extra wood clamp. So now the start is attached to a table or chair with two clamps. This makes the whole construction much sterdier.

Coding

I also did some minor coding updates.

Longer cable

The cable I brought was just a little to short, so I added a longer cable.

To store the whole track nicely till next year, I also build a nice chest around it.

All parts fit inside and the box itself is kept light. The stickers are just to make it look cool.

To keep it simple I changed the rules a little bit.

Perhaps the biggest change in the rules is the time they get: They won't be building this at home, so to bad for all the dads out there who would love to build a car. An other change is the weight. To keep the hassle with weights out of the way, the cars have to be very light. Finally they can only use the parts I provide, so no 30,- wheels in this cars.

The Rules

• You have to do with:
  
  • 1 44 x 33 x 175 mm block of wood
  • 4 3D-printed wheels (designs added)
  • 4 copper nails
• You have 2 hours to build your car
• Your car is allowed to weigh max. 100 gram
• You need to use all 4 wheels and all 4 nails
• All cars need a unique number or name written on them
• You have one run on each lane (so that's 3 runs)
• The fastest 3 cars go to the finale and have 3 runs against each other

Sure we also had trophies!

We had a trophy for:

• The fastest
• Almost the fastest
• Just fast

and one extra price for:

• Most promising

The trophies where also 3D print work. On top of the trophies I put the try out wheels that didn't make it to the final cut.

Everyone got a certificate with their name, the number or name of their car and the fastest time of their car. The logo for the trophies and certificates, I took from the internet, so I hope I didn't make someone angry. Next year I might design my own logo.

Designs for the trophies and certificates are also added. (Text is in Dutch)