Weight that defies Physics

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sdupont1
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Weight that defies Physics

Post by sdupont1 »

We were looking into racing to soapbox derby next year and ran across some news that I had never heard of or can't figure out. The weight limit is 200 lbs. Here is the situation:

All car are weighed with driver the night before. Now come race time, if your child can gain weight by the next day, then so be it. But here is the problem. Cars are weighed standing up on its back end and the nose pointing upward. The car and the driver combined weighs 200 lbs. When you take the car and lay it on flat or bottom, the combination weighs 215. Thats a hugh difference. I have talked to every possible friend of mine that is in engineering and this defies physics. I saw it myself. Also, the next car was weighed and it weighed the same on both the flat and the end, 200 lbs. The other car was put back on and it did the same thing, 200 and 215. Now the rules state that the car will be weighed on it back due to scale design so the car was allowed to pass and didn't infringe on any rules, only ethics.

So how is this possible to lose 15 lbs just by standing it on its end rather than flat?

Remember, there was one other, but the rest of the fleet weighed the same both ways.
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frontosacam311
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Re: Weight that defies Physics

Post by frontosacam311 »

Maybe something to do with the earths angular velocity at that given point in time and place. The earth spinning has to be taken into account. 15 pounds is a lot of weight though, enough to blow my theory out of the water. Stan, think were gonna need your'e help on this one! Corvid
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Re: Weight that defies Physics

Post by Stan Pope »

frontosacam311 wrote:Stan, think were gonna need your'e help on this one! Corvid
Well, been thinking about this all morning ... Earth radius way too large for differential g-force (tidal effect) to cause a 7+% change. The officials would have caught the kid getting into or out of his "lead BVD's".

Sounds like a scale issue. Some non-linearity in the linkage that translates forces on the scale pan to the measurement transducer???
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Re: Weight that defies Physics

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but why for just this car and 1 more and not the remaining 62. Placed the same car back on the scale after the remaining racers and it did it again. Clearly an isolated incident. Those two have something that no one else knows about yet. like I said, I wouldn't have believed it if I didn't see it. The funny thing is that we tried to duplicate it with other cars but they all weighed heavy in both directions.

The only thing that will affect the weight in that fashion is a spring, but the spring has to be anchored to the chassis of the car thus pulling the chassis down on the scale. I'm with you Stan, been stumped for a while.
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Stan Pope
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Re: Weight that defies Physics

Post by Stan Pope »

Sounds crazy, indeed.

For the vertical orientation of the car to "underweigh", then some of the system weight must not be translated correctly to the sensor. Possibly pan flex into part of the support, possibly lever flex that changes the fraction of weight that hits the sensor. Either could be affected by the footprint of the weighed objects and the location of the footprint on the pan.

Should never happen in a commercial scale, but ...
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Re: Weight that defies Physics

Post by Teeeman »

Something must be supporting weight... in the vertical orientation.

Either that or as Stan suggested it is an artifact of the scale itself not responding properly...


PICS PLEASE


-T
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sdupont1
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Re: Weight that defies Physics

Post by sdupont1 »

Something must be supporting weight... in the vertical orientation.

Either that or as Stan suggested it is an artifact of the scale itself not responding properly...


PICS PLEASE
Will have to wait till next year, the weigh in area was for organizers only. Which I thought was a good idea to keep all the people out, but the scale readout was in plain view. Those 2 cars could have come from Roswell as well as they were concealed after weigh in.
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Re: Weight that defies Physics

Post by Randy and Son »

How well did those cars perform?

Randy
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Re: Weight that defies Physics

Post by Go Bubba Go »

Teeeman wrote:Something must be supporting weight... in the vertical orientation.

Either that or as Stan suggested it is an artifact of the scale itself not responding properly...

PICS PLEASE

-T
If there's truly no add/remove slight of hand going on, I'm thinking it's gotta be a function (dysfunction) of the scale that the owners have discovered and figured out how to utilize. My guess would be that in the vertical orientation the weight is being placed very off center of the pan?

My other thought (but I would think people would catch this) is that a pin or screw or something is hanging over the edge of the pan, catching on the scale frame and supporting some (15 lbs.) of the weight.

Your "Houdini's" don't happen to know the "scale guy" and have non-event access, do they? Do the owners place their own cars for weighing, or does an impartial judge place the car?

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Re: Weight that defies Physics

Post by sdupont1 »

How well did those cars perform?
They won and the other third.
If there's truly no add/remove slight of hand going on, I'm thinking it's gotta be a function (dysfunction) of the scale that the owners have discovered and figured out how to utilize. My guess would be that in the vertical orientation the weight is being placed very off center of the pan?

My other thought (but I would think people would catch this) is that a pin or screw or something is hanging over the edge of the pan, catching on the scale frame and supporting some (15 lbs.) of the weight.

Your "Houdini's" don't happen to know the "scale guy" and have non-event access, do they? Do the owners place their own cars for weighing, or does an impartial judge place the car?

Bubba
I thought the same thing, they have a area of about 3' by 3' to set the car on. No lip to catch anything on. They weighed each car to the center as much as possible. Once this car did this, they weighed the rest and then came back to it. He could know something about the scale but it was not obvious.
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Re: Weight that defies Physics

Post by sporty »

We been racing soap box derby for three years, my son is 2008 local area champion, we are headed to Akron.

Never seen or even know this is legal in a aasbd race.


All races we have been to, are done with 4 pads and scale, flat and level.


My son races stock class car, 200 pounds.


I would report this one, if indeed true, all cars weighted in with driver in car in racing position. For total weight and checking for tail weight, depending on what the race is allowing for tail weight.

When the elite 8 are determined, they then re-way in. Esp for a local AASBD champ race !!


further note, this method of weighing for a official aasbd race is not legal, that I am aware of.

Also, there is a way to trick the load cells, if a load cell scale was used, esp if the load cells are not really the right ones in the scales.

The math program will just either round up or round down, depending on the software and load cells being used. this was more common on some older scales out there.

But this would only get you 4 pounds heavier, nothing like that much.

But they may be using the wrong load cell or not a very good math software program. Certainly this is not a normal or allowed official AASBD race weigh.

But drink 12 glasses of water and eat alot, you can gain weight fast with water drinking. lots and lots of it.

that is also a reason why they re-scale the top 8 for that race.

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Re: Weight that defies Physics

Post by sporty »

I will try and explain, what I felt I left out also.


Example,

a 65 kg load cell, or as little as a 35 kg load cell would be the more ideal and practical load cell to use for say a weigh of 200 pounds.

the match and software program is going to read the ohm readings coming from the load cells, that will intern provide a math reading, from what the software program was told from the ohm reading to provide.

The more common is, as I mentioned is people using scales or the wrong scale for the application of the weight reading.

Meaning, 400 kg load cell is going to maybe work, but not work properly, you may get buy with it, depending on how good the software match program is.

But you are asking a heavier designed load cell, that should for all practical purposes be used in the middle of the operating range at which the load cell was made for.

Thats why they make different kg load cells to being with.


But again what, really got me, is that the way they are reading a car and the driver, leaves alot to wonder how they are getting away with it, if it's a official aasbd race.


hanging a car and so forth ! load cell ? spring old scale ?

See, thats what i should have asked to begin with, what kind of scale ?

what about the tail weight rules ? they run no tail weight ? per most AASBD races ?


That process leaves a wide open area to cheat when it comes to tail weight. Thats for sure, unless they have no tail weight rule ?

Please, would enjoy hearing alot more details, before i make any more assumptions.


Sporty
sdupont1
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Re: Weight that defies Physics

Post by sdupont1 »

This is not a sanction race. Just the local packs that get together and put this on. The race is limited to 64 racers so its first come first serve (time constraint). If they win, they go no further, just bragging rights for a year till next years race. So as far as rules go, they are not goverened by anybody of state, just the local race committee. Things sometimes get heated but not too much. That is why they let him pass inspection because when weighed like the others on end, it passed.
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