It's Time for a Go/No-Go Box...

[Darin McGrew]

Well, our 2011 derby went pretty well. I saw lots of smiles, and we had only one car that wasn't crossing the finish line.

Last year, we had several cars that weren't crossing the finish line. All were cases where adults insisted that the axles were lubricated, when they hadn't actually been lubricated. A few drops of Krytox 100, and suddenly the cars were crossing the finish line with the other cars. (Not winning, but at least not humiliating their owners.)

This year, the car that didn't cross the finish line had been narrowed significantly, apparently being narrowed accidentally during the sanding process. Still, it seemed to fit the track (just barely) when tested. But the width of the guide rail varies slightly, and while it barely fit most of the guide rail, there were several places where the guide rail was just a bit wider, where the wheels pinched the guide rail. Once the axles were pulled out a bit more from the car body, it crossed the finish line with the other cars.

Narrowed cars seemed to be a theme this year. We also had one adult car disqualified from the All Comers race because it was too narrow. In that case, the adult replaced the block, but didn't get the dimensions right. He built a beautiful Porsche, but with its close-fitting wheel wells, there was no way to make it straddle the guide rail without major surgery, so he entered it for only the design competition.

Anyway, I think a go/no-go box could have caught the first car in time to avoid the humiliating DNFs, as long as it enforced just a little safety margin in the width of the wheel spacing.

[stang68]

The go/no go box is a great tool to catch problems like that. We provide one for all our Packs races in the District ,also a test weight that matches District scales.Since we started doing this our inspections are a lot less trouble.

[Stan Pope]

We provide one for all our Packs races in the District ,also a test weight that matches District scales.Since we started doing this our inspections are a lot less trouble.

What tolerances do you hold on the test weights that are distributed?

[stang68]

We made them using the scales that have been used at District for the last five years.They all read 5 oz on District Scales but since you can go to 144 grams before it will put a car overweight, we allow a car to go up to 144 grams on District Scales.This is noted and explained in the rules. I even took the scales to a Pack race today and cars matched up good on both scales with the test weight they used during tech night.

[Stan Pope]

Here is why I asked:

If the "pack standard" weights that you distribute are "certified" on the same scale you use at district race inspection, there are some issues that might "bite you in ... ummm ... tender places" The reason is that when you weigh a pack standard on your district scale, the actual weight of the pack standard is plus or minus 1/2 of the last place shown. (For instance, if your district scale weighs to one tenth ounce, each 5.0 "pack standard" actually weighs between 4.95 and 5.05 ounces.) Now, when the pack standard is used to calibrate the pack's scale, you lose another 1/2 unit. (Continuing the prior "for instance", a car that weighs 5.0 on their scale might actually weigh close enough to 5.1 ounces on the district scale to register as such, or might actually weigh close to 4.9 ounces on the district scale and be deprived of the benefit of another 0.1 ounces of well tested weight.)

A part that concerns me is if some packs get standards that actually weigh 4.95 ounces while other get weights that actually weigh 5.00 ounces and others that weight 5.04 ounces, there is lots of possible equity issues.

I don't have the experience to suggest the tolerance that should be used for such "pack standards", but I think I'd want at least one more decimal digit of accuracy than the scales used at district read out. For instance if you use scales that register nearest 0.1 ounce, then the "pack standard" should be accurate to nearest 0.01 ounce. The loaners that I keep for folks to borrow were weighed out to nearest 0.001 ounces, since our rules and district scales require 5.00 ounces or less. Still some possibilities for "gotchas", but I think that the probability goes way down.

Now, maybe somebody with more expertise can fill in the blanks and correct any errors I may have made here ... my "expertise" is all "technology transfer" from mathematics and physics.

Any "Six Sigma Blackbelts" around? Randy? ...

[stang68]

Stan,
That is what was happening at District each year with Packs using different scales.A lot of cars were going over weight on District Scales as well as some coming up a little short.Now that we use a standard test weight every one's cars are pushing the max. at District,if they are on the low side we allow weight to be added to bring them up to max. We make sure everyone is running the same max weight at District.

[Stan Pope]

Stan,
That is what was happening at District each year with Packs using different scales.A lot of cars were going over weight on District Scales as well as some coming up a little short.Now that we use a standard test weight every one's cars are pushing the max. at District,if they are on the low side we allow weight to be added to bring them up to max. We make sure everyone is running the same max weight at District.

Yes, I understand. But "what was" had different causes and different ramifications.

I'm not trying to "tear your accomplishment down." I'm trying to understand the details so that your accomplishment can be replicated by others. But parts don't mesh with what I know about the mathematics of measurement. That is why I'm still digging.

With the "pack standard" program, I expect that there will be fewer cars coming in "way off." My concern is that if every pack used their district issued "pack standard" conscienciously, it is very likely, with the tolerances you describe, that some will follow the rules, will pass the pack inspection as "exactly the same weight as the standard" on the pack's scale that has been properly calibrated with the pack standard, and will still be "too heavy" at district inspection. If that were to occur (and I think that it is certain that it does) then it would undermine the district credibility.

If district inspection is not turning such cases, then either the tolerance for the "pack standards" is tighter than advertised or the cause for the exceptions that come in overweight is not being recognized.

[dna1990]

We built a new box this year - and didn't really look close at the old one. Went with newer design.

Anyway, made the straddle check strip the full 3/8" tall, as is the common ground clearance spec. We had ALOT of cars with the usual PineCar style weight grates attached to bottoms, that would not pass this check.

We hand checked those on the track itself (which I believe is just proud of 1/4", maybe by 1/32"). They were going to roll fine, and we allowed to pass, since this was an abrupt change from last year.

What is the concensus on ground clearance, esp given that many non-tungsten car builders go for the weight plates underneath? Do you stick with 3/8"? Does your track really require a full 3/8"? Do you remind/require people not to attach weights on the bottom?

In our sizing box, we give 1/8" extra to the side and length dimensions. But even an 1/8" off the guide strip check would not have passed a few of them - even though they traversed our track without issue.

[gpraceman]

We built a new box this year - and didn't really look close at the old one. Went with newer design.

Anyway, made the straddle check strip the full 3/8" tall, as is the common ground clearance spec. We had ALOT of cars with the usual PineCar style weight grates attached to bottoms, that would not pass this check.

We hand checked those on the track itself (which I believe is just proud of 1/4", maybe by 1/32"). They were going to roll fine, and we allowed to pass, since this was an abrupt change from last year.

What is the concensus on ground clearance, esp given that many non-tungsten car builders go for the weight plates underneath? Do you stick with 3/8"? Does your track really require a full 3/8"? Do you remind/require people not to attach weights on the bottom?

The issue is really on the track curve and with weights placed low on either end of the car. That is where you will need a bit more than the 1/4" height of the guide strips for clearance. I think 3/8" was used originally to give a little fudge factor to ensure cars would not drag on the curve. If you had a straight incline track, you could use a clearance checker only 1/4" tall, but with curved tracks, you will need a bit more clearance. The tighter the track curve, the more clearance will be necessary.

We would check on the track as well for any car dragging on the clearance checker, but we would make sure to do that on the curved section.

[Rukkian]

It will probably only come into play if you have a car with the orginal wheelbase (or smaller) as cars that have the wheels pushed to the outside, should be fine on the curve.

[dna1990]

curved section.

Agree, and we did check it there. Ours is a wood track with 'natural' curve, nothing too abrupt.