Derby Races > Build Tips
1. PLEASE READ THE RULES.
2. PLEASE TALK TO YOUR DAUGHTER ABOUT SPORTSMANSHIP.
3. Impound Day - All cars must be impounded prior to the race. Impound Day is on Sunday, March 26, 2017 from 10:00am-2:00pm at the Brady Garage - 1105 274th Place SE, Sammamish, WA 98075 (Trossachs neighborhood) 425-281-2295. If you are unable to attend, please send your car with another Scout family or your troop leader. Be sure to come early if you need some help adjusting weight.
4. Shape Your Car - Basic race car shapes (templates attached with flyer) can be easily cut using a coping saw and c-clamp (about $12 at Home Depot). The girls can do this! After a little sand paper on the rough edges, the car is ready to paint. We usually use acrylic craft paint but you can use any kind of paint.
5. Car Dimensions - The dimension guidelines are in place to accommodate 4 cars racing side by side down the track (maximum W=2 3/4", L=7", H=4 3/4" & ground clearance=3/8"). The block of wood that comes in the car kit already meets the requirements. You do not need to measure your car unless you add something to the sides, top or bottom. If cars + decorations are too high/wide they may hit the finish line arch or other cars.
6. Weight is Important! - The cars race on a gravity track so weight is the single most important factor when it comes to speed. Cars can weigh a maximum of 5oz. Depending on the shape/decorations, a finished car will weigh about 3oz. Weight can be added anywhere any way. There are a wide variety of weight kits available ($4 at Michaels, also available from Amazon). You can use rods, flat plates, hardware washers, fishing weights, coins...anything! We have had great success with drilling holes in the back of the car (looks like tail lights) and stuffing with the rod shaped weights. Tungsten weights (MUCH more expensive $20+) are smaller/heavier and definitely provide a speed advantage (better placement at center of gravity). If you decide to add the flat plate weights to the bottom of your daughter's car, I highly recommend carving out a pocket to recess the weight a little bit. If the car does not maintain 3/8" clearance from the track it will bottom out, scrap the center guide and slow down a lot.
Michaels has a limited supply of car weights available. I was informed it is the end of derby season and they do not plan to restock. You may want to call first or order online.
Scouts usually use a food scale or visit the post office to check their car's weight. On Impound Day, all cars will be weighed on the official SU digital scale. Final adjustments can be made to bring your total weight to 5oz. Please bring extra weights with you.
7. Axels and Wheel Preparation - We never do any of this but there are lots of kits and tips online (smooth wheels, polish axels, straighten axels...).
8. Add Your Wheels - The second most important speed tip is wheel alignment. Straight wheels go faster! If the car does not roll straight, adjust the wheels. Those nail slots can be a little tricky. We have had great success with drilling pilot holes for the axel nails (I have two Revel Axel Alignment tools if anyone would like to borrow, $10 from Amazon if you want to purchase your own). We also make sure the wheels spin freely. If the nails are pushed in too far, the wheels will scrape against the body of the car. We have never attempted advanced "rail rider" wheel alignment.
9. Reduce Friction - An aerodynamic shape and straight wheels will reduce friction. No need to purchase graphite powder for the wheels. We will have plenty available at Impound Day.
10. HAVE FUN! It is fun to win but my daughters' favorite memories are of time spent with their family building cars. Please let us know if there is anything we can do to help you and your girls!