Monday, May 25, 2015

Pinewood Derby Race Set

This could hardly be considered a wood carving but since it is made from wood and this is my blog: So it qualifies! 

It was recently decided that my wife and I would have Grandkid duty for a couple of days in the early part of June while our daughter is working.  They live in another town so we have been thinking about the types of things that we could/should take with us to entertain two 7 years olds and two 8 year olds for long stretches of time.  One of the things that we came up with was a pinewood derby set.  Any race track design carried with it an additional requirement: it had to have the capability to be disassembled for transport.

Four Completed Cars Ready to Race
I started with the cars.  I went to my favorite hobby store with the intent to buy four Official Cub Scout Pinewood Derby car kits.  As it turns out, doing that wasn’t as easy as it might have seemed it would be.  I was there in late April only to discover that the “official Pinewood Derby Racing Season” was over and that all of the “regulation” car kits had already been pulled from the shelves and stored for next year.  All that remained on the shelves were the fancy, to say nothing of expensive, brand name kits.  Some of these kits cost as much as I had hoped to spend for the entire set…and that was just for one car!

 They did, however, still have sets of official Pinewood Derby wheels on the shelves so I snatched up four sets and went home.  Fortunately, Basswood is something that I got a lot of, so I figured that I would just design and build my own cars.

Note the track alignment pins protruding from the tops of pylons
Visions of fancy race car designs danced in my head as I drove home but after a quick sobering walk around the block I realized that to show up with four different cars was only to ask for problems as far as which kid got which car.  I decided that it was a better idea to make them all exactly the same.  I  settled on a relatively bland 1930s, open cockpit, retro race car design and made four cars as identical as I could.  Their mother specifically requested that no “kid painting” be involved…hmmm…Gee, I wonder why. :-)  So, I sprayed them with a coat of polyurethane and we purchased some details so that the kids could personalize them. 

I thought about the track for quite some time and finally decided that 3 pieces of ¼” Luan underlayment (15” x 48”) connected end to end would make a reasonable race track.  Easy to assemble and transport. I built 3 pylons of progressively lower heights to support the race track.  

Each pylon has a set of dowel pins sticking out of its top to lock the track sections together.  I added a tab to the underside at the upper end of each track section to force it to be flush with the next higher track section to minimize the chance of a bump where two sections meet.  The idea works “pretty well”, but not perfectly.  You do have to run your fingers over the seam to make sure that everything lines up correctly and adjust things accordingly.

I ripped down a number of ¾” wide strips from the same Luan sheet and glued them to the track sections to form the lanes.  If I was to do this over again, I would either use something thicker or glue down a second strip on top of the first one, because the cars “can” still jump the rail.

Track and Pylon Details
I made the pylons out of more pieces of the Luan glued together with blocks in the corners for strength.  I used thicker pieces of pine along the inside edges at the end of each pylon to give the alignment dowels something substantial to be glued to.  The original Pylon heights were 6”, 4” and 2” with about a ¼” slope (in the direction of travel) to the top.

I had done some preliminary testing to see how much height I would need to give the cars a decent starting speed to make it a real race.  At first, it seemed that a 6” high starting pylon to be plenty high enough.  But, after completing the entire course I discovered that I really needed another 4” or so at the top to really get the cars moving at a speed that a 7 or 8 year old would like.  So, I build a four sided box with a rabbit around the inside for the original first pylon to sit down into.  Fortunately, because the track is relatively flexible, I discovered that the other two pylons could remain unaltered.  This 10+ inch high starting point sends the cars off at a nice, exciting speed.
I used polyurethane on the track sections and used some red, white and blue spray paint to give the pylons a little added flair.

Starting Gate
The starting gate is partially my design but the concept is based on a “how-to video” that I found on the making a Pinewood Derby race course.  The design uses a main shaft (a piece of ½ plastic pipe) to hold four short pieces of ¼” dowel that stick up through the track, one in each of the four lane of the track.  Each car is positioned on the track with its nose resting against one of these car retaining pins.  
The main shaft is mounted to the underside of the top section of the track using 5 blocks of wood.  A ¼” dowel runs through the support blocks to act as a “stop” for the car retaining pins after the gate has been released.  

 One end of the main shaft has an elbow and a short piece of pipe that form a handle used to “cock” the mechanism.  The other end has a small cylindrical collar fastened to it.  
View of Underside of Starting Gate
 The gate release is a short section of ½” dowel that sits in a short length of plastic pipe.  The gate release is locked into a hole on the perimeter of the collar by a spring located in the base of the pipe.  When the gate release is retracted, the main shaft, which is rubber band powered, is released and rotates forward.  Each of the dowels snaps down through its slot in the track, releasing all four cars simultaneously, auto-cross style.  

The rubber band used to “power” the starting gate is looped over the car retaining pin in the second lane (going l-to r) and is stretched to the retainer under the track near the top edge.

Operation of the Starting Gate


How Well Does it Work?   You be the judge!  Yeah, there was a bit of bumper cars goin' on there:-)


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