Bodies for SPEED!!!

[RACER X]

What have you had the most sucess with body shape wise when building for speed?

We built a lightened nose wedge with a high nose scoop for faster starts. Our tracks have manual gates, the high nose really helped.

It won pack and districts for us this year.

What's hot for you.

[Stan Pope]

So long as you don't "get ridiculous", e.g., a 4-masted schooner with sails, the body shape can be dictated by other goals. For instance, how can I get the CM located where I want it for min ET? Or, more importantly, how can a youngster get his CM where he wants it? Consequently, ease of construction in absence of fine motor skills is pretty important.

A "forgiving design" that is not so thick as to require special tools is really helpful. A basic platform 1/4" thick can be worked in steps that are within the attention span of most 7 to 10 year olds. It is thin enough that a coping saw (or table scroll saw) works for them. And nose shaping happens easily on a disc sander.

Make it easy for them to install weights. (Large vertical through holes and epoxy or bondo rather than 3/8" horizontal holes, etc.)

See example of this philosophy at http://members.aol.com/standcmr/vicpwc.jpg
It is okay that it looks like an 8-year old built it. It still went undefeated at his pack and council races!

Note that it does have a slightly elevated nose. I think that the gates were operated briskly enough that it played no role.

[Darin McGrew]

So long as you don't "get ridiculous", e.g., a 4-masted schooner with sails

Hey, I resemble that remark...

(My "Calvin and Hobbes" car was too tall to fit under the finish gate. Each time it raced, I had to catch it before the finish gate decapitated the figures. Fortunately, it was slow enough that the finish order was never in any doubt when I did this... )

Consequently, ease of construction in absence of fine motor skills is pretty important.

This is a real issue. I don't always follow my own advice, but I encourage the kids to KISS with the design. For both speed and design, it's more important to do a great job with a simple design than to do a mediocre job with a complex design.

And nose shaping happens easily on a disc sander.

Some of the most popular tools we have at our workshops are the bench sanders. It's really easy for the kids to shape their cars with these.

[MERuhl]

Stan - how much weight do you typically have to add to that design to get it up to 5 ounces?

[Stan Pope]

Stan - how much weight do you typically have to add to that design to get it up to 5 ounces?

Well, lessee... wheels and axles weigh around an ounce, wood body, what there is of it, weighs around a tenth of an ounce, so, figure about 4 ounces of lead (and epoxy). Can you guess where the lead is hidden?

[Stan Pope]

So long as you don't "get ridiculous", e.g., a 4-masted schooner with sails

Hey, I resemble that remark...

For you, Darin, I would not consider a 4 masted schooner ridiculous... except possibly that you would normally have 5 or 6 masts???

Seriously, aerodynamics are not the make-break issue except at the very highest levels of competition. Even then they are important only when everything else has been done exquisitely well. I don't think that cutting a quarter square inch off the cross section is nearly as important as getting the wheels and axles worked and aligned exactly "right".

But, if you add 60 square inches of sails, well ...

[MERuhl]

Well, lessee... wheels and axles weigh around an ounce, wood body, what there is of it, weighs around a tenth of an ounce, so, figure about 4 ounces of lead (and epoxy). Can you guess where the lead is hidden?

BSA wheels and axles weigh an ounce? Huh...the Awana kit's wheels and axles weigh in at just half an ounce. Guess I can stick a couple more tungsten cubes on the back than you can!

[Da Graphite Kid]

MERuhl,

My youngest son built one of Stan's rail (ladder frame) cars last year and I weighed the body only (0.54 oz.) and the wheels and axles only (0.63 oz.). This left 3.83 ounces for tungsten weight, paint and decals. I've built two before we had scales to weigh things on so these are the only weights we have for this design.

I would like to point out that he had two weeks in which to build this car. It was done in three days!


Da Graphite Kid

[MERuhl]

Thanks, Kid. Those measurements are consistent with what I've observed, and was able to calculate using the density/volume conversion charts at www.allmeasures.com

How well did that car perform?

[Stan Pope]

My youngest son built one of Stan's rail (ladder frame) cars last year and I weighed the body only (0.54 oz.) and the wheels and axles only (0.63 oz.). This left 3.83 ounces for tungsten weight, paint and decals. I've built two before we had scales to weigh things on so these are the only weights we have for this design.

I would like to point out that he had two weeks in which to build this car. It was done in three days!

Body sounds a bit heavy. Many are fearful of removing more wood than that!

Thanks for adding detail on wheel/axle weight ... my numbers were from memory of casual weighing of stuff, not a very reliable source!

Haven't used tungsten... can it pounded into various shapes, like lead?

[MERuhl]

Stan - I came up with a number very close to that for the wood body yesterday, using the following method:

(front axle area = .25"x1.75"x.5") + (2 rails each = .25"x.25"x5") + (rear axle/weight-holding area = .25"x1.75"x1.5") = 1.5 cubic inches of wood, which according to the volume-to-mass conversion chart for "Southern Pine" at http://www.allmeasures.com/Formulae/sta ... ity/43.htm should weigh 0.5115639958376692 ounce.

So next year we're shooting for a combined wood/wheels/axles weight of 1 ounce, so we can concentrate 4 ounces of tungsten right where we want it.

Haven't worked with the tungsten yet, so I don't know about its malleability, but I do know it is not toxic. It's sold in .25" cubes, so it should be easy enough to work with.

[terryep]

I believe Tungsten is very hard and can only be cut with abrasive wheels. Tungsten welding rods are a possible source. Tungsten powder (used in some ammunition) should be avoided as it is pyrophoric! http://www.acialloys.com/msds/w.html

If you know the weight you need and want to get it into the smallest most affordable package Tungsten is ideal. I prefer to use whatever I have in my workshop.. brass or steel.

[MERuhl]

http://www.maximum-velocity.com/speed_s ... m#Tungsten

[Stan Pope]

Stan - I came up with a number very close to that for the wood body yesterday, using the following method:

(front axle area = .25"x1.75"x.5") + (2 rails each = .25"x.25"x5") + (rear axle/weight-holding area = .25"x1.75"x1.5") = 1.5 cubic inches of wood,

Nice work!

I see part of the problem, though. Way too much wood! Enough for 2 cars, almost!

Now...
lengthen and taper the front axle area, full thickness only at the axles.
reduce the rail width to 1/8".
reduce the rear axle/width holding area to 3/8" X 1/4" X width ... only center wood around axle ... void fore and aft.
and recompute.

Doesn't get down to 0.1 oz, but should be well below 1/2 oz.

[Da Graphite Kid]

Stan, I couldn't get him to go thinner or remove any more wood than he did. We were both fearful of the stop block at the end of the District track and intentionally left extra wood up front. If you break the front end out of one of these there just isn't much left to glue back together (and it will get broken out next time down the track). I've thought about running a piece of cloths hanger wire around the front edge to help strengthen it but the best 'fix' would be to change to a better track stop section.

As for working tungsten - we don't even try. I tried drilling some out last year as I mis-guessed the amount I could put in one of my cars and it was a very slow process. The result was that I heated the tungsten up more than drilled it and a piece fell out of the epoxy. On my sons car and the others I built, we just got 'close' and than added the store bought weight plates and used modeling clay to get that last 0.01 ounce.

The car was fast but there were four others that were faster - real close racing. I think that the 'home track advantage' did us in - but at least he was faster than his brother and he was quite happy about that!


Da Graphite Kid