March Meeting: Pinewood Derby
For the March Guild meeting, Guild members got to do some woodworking instead of just learning about it. The meeting was a Pinewood Derby held at The Mill in northeast Minneapolis (www.mnmill.org), a small scale production facility and maker shop for Mill members and people taking classes there. The Mill has finished setting up shop, and their first community open house is Saturday April 21, 10:00 a.m. to 2:00 p.m.
It was a beautiful Saturday afternoon, so attendance was sparse, with about a dozen Guild members taking part. Mike Thomas brought his three young sons, who added just the right level of enthusiasm.
Pinewood Derby car kits were available free to Guild members. Each one had a block of pine 7” x 1 x 1-3/4” wide, with four plastic wheels and four nails for axles. Each block had two slots in the bottom to hold the axles. Guild members used their own hand tools, Mill tools, and bench top power tools brought by Guild member Jeff Hand.
While Pinewood Derby rules limit car length to 7”, width to 1-3/4”, and weight to no more than 5 ounces, with no added bearings or mechanical devices, that still leaves a lot of room for creativity.
Car designs varied a lot among the eleven competitors. The simplest was an unadorned block with wheels. Mike Siemsen shaped his car with a very sharp hatchet on a chopping block the size of a 3-pound coffee can made from a section of tree branch on three splayed legs.
The curves of another car suggested a Formula I car, and needed only a coat of British racing green paint to look like one of Jackie Stewart’s Grand Prix winners. The cars had names like The Rock, The Mill, Packer Backer (in green and gold livery), Axe Minister, The Basic Beast, Hammer Head, and Bling (done up in black and gold).
Members learned about the fine points of Pinewood Derby car construction. The first and most important thing is to keep all four axles parallel to the ground, perpendicular to the sides of the car, and the same distance from the ground. Second, sand or file off any ridges on the axles to reduce friction. Powdered graphite can be used as a lubricant on the axles. Third, make sure the wheels are not too close to or too far from the car body; otherwise they will bind or wobble.
Air drag is not that big of a deal. For you technical types, drag mainly depends on the square of the car’s velocity, and Pinewood Derby cars don’t go that fast. A smooth car will look better, but other factors are more important than being aerodynamic.
The biggest factor is weight. Even though Galileo proved that heavier objects don’t fall any faster than lighter ones (and Jim Irwin demonstrated it on Apollo 15, when he dropped a falcon feather and a hammer on the airless surface of the moon and they hit the ground at the same time), a car that just reaches the 5 oz. limit will have an advantage. It probably has to do with better traction on a heavier car, or less bounce along the track. Whatever the explanation, it works, and The Mill had plenty of cabinet hardware, nuts, and washers to use as weights on the cars.
|Two cars race to the finish line in a close heat|
The two-lane wood track had a car release at the top of a downhill section four feet high, ran for about 32 feet, then had an uplift at the end where the lane guides continued upward but the track surface did not, bringing the cars to a safe stop. All the races were captured on video.
After several exciting heats, the winners were:
First Place – Greg Flanagan
Second Place – Mike Siemsen
Third Place – Kyle Thomas (son of Mike Thomas)
|Greg Flanagan||Mike Siemsen's Car, Trophy and Prize||Kyle Thomas|
A splendid time was had by all.
Click the play button below to watch a one minute YouTube video of several heats.