Kub Kars are gravity-powered wooden model cars built and raced by cubs. Usually, there is an annual rally held in the ACT, with nearby groups in NSW also invited to attend.
The rules are designed to encourage creativity and engineering skills, balanced with ensuring that the racing competition is fair.
Programming
In the ACT, Kub Kar rallies are usually held in May or June each year. While some online resources suggest that you can introduce the concept to the cubs and have them design the cars and shape them in one session, it is far better to use the Kub Kars as an opportunity for the cubs to get one or two Special Interest Badges (Science & Innovation and Arts & Literature), and to round out the learning opportunities with foundational programmes. The Kub Kar race is a great way to learn about physics and design. This is the obvious element. What about the aesthetic element? What colours go well together? What surface treatments could be applied?
The main elements of a fast Kub Kar are 1) maximising gravitational potential energy, 2) minimising wheel friction and 3) minimising wind friction. Building up to the Kub Kar design with some fun programmes that address these physical forces can be educational and reinforcing. An egg drop challenge can provide an understanding of the value of having a car that is as close to the maximum weight as possible. If the egg drop challenge activity includes parachutes you bring in air friction.
Most of the Kub Kar paradigm is focused on how to remove wood from the original block. You could spend an evening exploring methods for adding material on top of the block - Lego, papier mâchê, hot knife and foam (be mindful of the fumes).
Hardware kits
In Australia, Kub Kars can usually be made of any wooden material. Pine is the material of choice because it is relatively light, cheap and is relatively easy to work with. As a leader you have two main options for providing the basic hardware for cubs to start with. You can order the complete kits from Canada or the US, or you can chose the more environmentally friendly option and buy the wood locally. Unfortunately there is no Australian source of suitable wheels and axles.
Complete kit
You can order complete kits from Scouts Canada or Scouting America. These options are relatively expensive and involve shipping high density pine half way around the world.
"Bunnings Buggy" option
This is a hybrid DIY option that is well-aligned with the Scout Law. It is thrifty and mindful of the environment, and it supports Australian industries.
- Order a bulk pack of wheels and axles from somewhere like Maximum Velocity. You will probably want to include an axle drilling guide. You should allow about 2 weeks for the package to arrive and you can save on packaging costs by clubbing together with nearby groups for a bulk order.
- Buy a #44 drill bit. There is no direct metric equivalent to the #44 drill bit. A 2.0 mm drill bit is a bit tight. When last checked, refast.com.au had them in stock and were the best price in Australia.
- Go to your nearest hardware store and buy a length or two of 42 x 19 mm DAR pine. Check the pieces carefully for straightness. Despite being "Dressed All Round", they can still have twists if they were not dried carefully before milling. This material normally comes in lengths of 1200 mm or 1800 mm. The maximum length of the cars is 180 mm, so you should be able to cut 6 cars from a 1200 mm length or 9 cars from the 1800 mm length. It helps to find a dropsaw to cut these lengths. Pro-tip: Carefully measure and cut one car, then use it to set the lengths for cutting the others.
- Mark the axle locations on the blanks and use the axle drilling guide to drill the axle holes.
Design Templates
There are many design templates available online.
Rules
The rules for Kub Kars are moderately simple.
For all cars, the underside of the car must be bare wood and have the name of the cub and the year. Each year, a new car needs to be made. The cars need to have a wooden core.
No suspension is allowed.
For cars that are being entered into the racing competitions:
* Maximum weight: 142 g
* Maximum length: 180 mm. This includes any decorations like exhaust pipes.
* Maximum width: 70 mm
Minimum distance between the wheels is 42 mm. This is slightly narrower than the Canadian standard of 45 mm to accommodate the standard size DAR pine in Australia.
* Maximum height: ?
* The wheel size cannot be altered.
* Wheels can be lubricated with graphite powder, but not liquid lubricants.
* Only the Kub Kar owner can race the car.
* The judges decision is final.
Guidance for a fast car
PLEASE REMEMBER - this is meant to be a fun and educational exercise for youth, not a race between parents or adult leaders.
Choose a design that is low profile.
Do not place any weights under the car so that they protrude below the base of the car body. This can cause the car to drag on the centre guide rail. If you want to place the weights under the car for aesthetics, then hollow out the underside so that the weights can be glued inside the hollowed out section.
Maximise the total weight of the car up to the allowable 142 g and try to set up the centre of mass to be about 25 mm in front of the rear axles. This is to help ensure that the front wheels don't lift off and flick the car off the track.
Try to reduce friction between wheels and axles, between wheels and the car body and between wheels and the guide rail. Check the axles where the hub will run. If this area is not very smooth then use a power drill to spin the nail and polish the area with fine sand paper.
Place the axles in the car, leaving about 0.5 mm gap between the hub and the body. Check that the car runs straight.
Paint it red, because ...