Building a new car for our second year.

[rpenning]

Ok I am better prepared for this year, I have two weeks to build three cards, not an issue as I already have the cars and all the tools. Here are the rules I have to follow.

1. LENGTH, WIDTH, HEIGHT, & CLEARANCE

a. Maximum overall width (including wheels, axles or other parts) shall not exceed 2 ¾”.
b. Minimum width between wheels shall be 1-3/4” so the car will clear the center guide strip.
c. Maximum height shall not exceed 3-1/2” so the car will clear the race timer.
d. Minimum clearance between bottom of car and track shall be 3/8” so the car will clear the center guide strip.
e. Maximum length shall not exceed 7”.

2. WEIGHT AND APPEARANCE

a. Weight shall not exceed 5 ounces. The readings of the Official Race Scale will be considered final. (use a bit of leeway as den scale may have been off a tad) The car may be hollowed out and built up to the maximum weight by the addition of wood or metal only, provided it is securely built into the body of the car or firmly attached to it. No loose materials of any kind will be permitted in or on the car. The bottom of the car must be smooth in order not to damage the car stopping area of the track.
b. Mercury or other liquids shall not be used for adding weight. Mercury is a potential health hazard.
c. Details such as steering wheel, driver, spoiler, decals, painting and interior details are permissible as long as these details do not cause the car to exceed the maximum length, width, height, and clearance specifications already listed.
d. Cars with wet paint will not be accepted.

3. WHEELS AND AXLES

a. Only the official Scout Grand Prix wheels and axles can be used. Wheels must have “Official B.S.A,” stamped on the wheel rim.
b. Wheels can be sanded to remove surface imperfections, but the surface that touches the track must be left flat and at least ¼” wide.
c. Wheel bearings, washers or bushings are prohibited.
d. The car shall not ride on any type of springs.
e. The car must be freewheeling with no starting device or propulsion.
f. The wheel base location of the car may be adjusted as long as you still adhere to the maximum length, width, height, and clearance specifications.
g. Hubcaps or similar items used to keep the wheels lubricated are prohibited.
h. Spoke wheels and/or modified wheels are prohibited.


Now with these rules I think I can do a lot but to make sure I am making the best choices in design and modifications I want to get some input. The track we will be using is an aluminum best track I think. I was planning on extending the wheel base as much as possible so that the ends of the wheels are the limits of the length. I was also going to drill new axle holes and lower the body, do I need to do that on the front and rear or just the front. I was going to make the right front wheel the dominant wheel and also move it inwards to the center of the body a 1/16th of an inch. Raise the left front wheel so that it is not touching the track and follow the rail rider design plan. I was wondering about canting the rear wheels and also the suggested COG. Last is the weight placement, not sure on that. I appreciate all input and suggestions.

[oddzilla]

Here's what we used this year. It was a basic template I made up for the scouts in my Den to give them an idea on how to start. It's based off an old Hodges manual I have but I just modified the design to make it as low-profile as possible.

For the first one, it uses the default wheelbase but drilled holes instead of the slots (as I found out, there were quite a few blocks that had inconsistent slot heights). With the height of the front, it allows for raising one wheel an extra 1/16" for a three wheel car.

Also, the holes allow for 3/8" lead wire for weight. With the depth of the holes, it will take a 1 1/2" 1 ounce peice of lead wire in each hole. You can find that off ebay (I generally get mine from Pinewood Derby Den, but many dealers sell it pre-cut). Just fill it with bondo or wood filler and sand flat.

The second one my son wanted to move the wheels back so this is the basic configuration in the hodges manual, just modied for the thin wedge style.





As you can see, the only difference is the rear axle being pushed back and the weight spaced slightly differently. Note, I used the second template but moved the front weight back to 1/16" in front of the middle weight and the distribution wasn't as good as I came in fifth overall even though all of our cars were built the same and axle and wheel prep the same. I attribute it to the weight placement.

The only thing we did to the wheels was polish the bore with Derby Worx bore prep. Axles were files and sanded to 1500 grit only and we used Derby Dust graphite.

Here are the results on an 32' aluminum track with about a 29' pin to win run:


Again, my son used Template 2.

My son's Rank Race - Webelos I.
Race # Lane # Time Place Speed (mph)
1 3 2.3570 First 209.7 Fastest Time in rank
2 2 2.3670 First 208.8
3 1 2.3650 First 209.0
4 4 2.3620 First 209.3

He took first place in rank. Here's the grand finals:
Race # Lane # Time Place Speed (mph)
1 2 2.3690 First 208.7
2 1 2.3620 First 209.3
3 4 2.3700 First 208.6
4 3 2.3570 First 209.7 Fastest Time over-all

He took first in rank and first over-all for the day and moves on to Districts in April.

My daughter used Template 1:

Here's my daughters results for Open Junior:
Race # Lane # Time Place Speed (mph)
1 1 2.3610 First 209.4
2 3 2.3630 First 209.2
3 4 2.3600 First 209.5
4 2 2.3590 First 205.5

She took first in Open Junior.

My wife also used Template 1:

Here's my wifes results from Open Adult:
Race # Lane # Time Place Speed (mph)
1 1 2.3740 First 208.2
2 4 2.3580 First 209.6
3 3 2.3700 First 208.6
4 2 2.3650 First 209.0

She took first in Open Adult.

And, then there was mine (sad trombone sound):

I used Template 2, but as mentioned moved the weight back which I feel turned out to be my undoing.

Race # Lane # Time Place Speed (mph)
1 2 2.4090 Third 205.2
2 1 2.4470 Third 202.0
3 4 2.4090 Second 205.2
4 3 2.4130 Third 204.9

To finish up getting weight to as close as 5.00, I used tungsten putty and lead tape when necessary. They were all about 4.99.

We ran out of time this year as our derby was moved up 2 months so I talked everyone into going simple. These were the fastest, easiest cars to drill cut, sand and weight and they turned out to be the fastest cars in our derby. Go figure!



And of course, after the race everyone asks how we did it when the whole time since we announced the derby I told anyone I can help with anything they need. It's no secret and I have no problem sharing. At least one in my den took what I had to tell and used it in their car. He came in 6th in rank.