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Post by Professor Moriarty on Oct 8, 2017 22:39:59 GMT -5
That was exactly what I had thought originally. Spreading the weight should increase the MOI on that axis...
I cannot remember the analogous thing that I had watched that made me seriously question this assumption... (or at least think that centerline weighting may be faster...)
It may have been the video about the solar powered car that goes long distances?
Unsure... it will probably come to me.
Maybe it is right... maybe it isn’t...
I do recall Goaskgrandpa.com arguing with his physics buddy about which is the best weighting scenario (aero and other factors aside)
Grandpa is a physicist too and he said a sphere... his buddy said a cylinder across the axles.
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Post by Professor Moriarty on Oct 8, 2017 22:50:38 GMT -5
I am thinking that MrD probably tested a car with a “good” drill job without weights and it didn’t rub the rail... then he took out some weight and put the side weights on it and it rubbed the rail...
So...
Either the weighting balance paradigm needs to shift due to some of the weight being shifted directly on top of the contact areas of the axles and wheels...
Sort of like the guys that hang off the side of a catamaran...
Or...
Any small amount that the drill job is off... is amplified by the side weights causing the rears to hit the rails.
And it may be something simple like shifting a lot more weight on one side or the other... but I doubt anyone ventured outside the box to test for something like that.
the first year the full weights came out... the freshman Bullet used them to win the nationals or take second place... can’t remember...
so he figured out how to use them without getting the wiggles.
Actually... I guess there are a host of other reasons why the car wiggled in Mr D’s test after it ran fine previously...
but if i know Mr. D then he performed this test on multiple cars and probably even pulled the weights off to run it conventionally again... in order to rule out any variables other than the weights.
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Post by Professor Moriarty on Oct 8, 2017 23:07:47 GMT -5
Again though...
It is a completely different weighting system though... so the normal things may not work...
He probably wants to keep a certain amount of weight on the front wheel... this is one reason why in conventional weighting a fella will put a cube or two on a third row in front of he axles on the extremem right.
To balance the rears while keeping some weight on the front wheel so it won’t lift off the rail.
When balancing cars with the weights you find weight on the front wheel quite naturally... and yet the weight is higher on the hill.
In other words...
While I am sure Mr. D tested for things that were went along with a normal build...
I question that he was able to test some of the farther out ideas. Maybe the normal guidelines do not apply.
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Post by micro on Oct 9, 2017 7:33:47 GMT -5
I believe(Know) that I have mentioned this before.......Think of the golden triangle....think of a car with wheel weights on both sides....what is wrong with that picture? Do I need to connect the dots more that that? Again?
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Tungsten
Oct 9, 2017 7:51:46 GMT -5
via mobile
Post by Chuy on Oct 9, 2017 7:51:46 GMT -5
Micro, it is customary in physics and in engineering to look at weight distribution and reduce it to the center of mass (CM). What this proven convention does is allow the simplification of equations. So by this convention, locating 2 oz one inch outside of each rear wheel is equal to a 4oz weight centered between each wheel. You do increase the moment of inertia in this plane, making it harder to rotate on the horizontal plane but CM is the same. As a good example of this effect, consider the pole a tight rope walker carries. By what is being described here, it would make him less stable.
DISCLAIMER: I'm not saying this behavior does not happen, just saying I'm not understanding how it happens. I would like to know more
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Post by Vitamin K on Oct 9, 2017 10:46:31 GMT -5
Micro, it is customary in physics and in engineering to look at weight distribution and reduce it to the center of mass (CM). What this proven convention does is allow the simplification of equations. So by this convention, locating 2 oz one inch outside of each rear wheel is equal to a 4oz weight centered between each wheel. You do increase the moment of inertia in this plane, making it harder to rotate on the horizontal plane but CM is the same. As a good example of this effect, consider the pole a tight rope walker carries. By what is being described here, it would make him less stable. DISCLAIMER: I'm not saying this behavior does not happen, just saying I'm not understanding how it happens. I would like to know more Would it be possible to rig up a test similar to this one to gauge the "wobble effect" that wheel weights might (or might not) produce? |
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Post by Professor Moriarty on Oct 9, 2017 11:59:05 GMT -5
The golden triangle is mainly used as a reference for keeping the raised wheel from bobbing up and down.
Weight behind the axles does not fall within the golden triangle either...
i have always considered areas not inside inside the golden triangle or inside the bizarro triangle as somewhat an unknown quantity.
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Post by Professor Moriarty on Oct 9, 2017 12:08:19 GMT -5
Micro, it is customary in physics and in engineering to look at weight distribution and reduce it to the center of mass (CM). What this proven convention does is allow the simplification of equations. So by this convention, locating 2 oz one inch outside of each rear wheel is equal to a 4oz weight centered between each wheel. You do increase the moment of inertia in this plane, making it harder to rotate on the horizontal plane but CM is the same. As a good example of this effect, consider the pole a tight rope walker carries. By what is being described here, it would make him less stable. DISCLAIMER: I'm not saying this behavior does not happen, just saying I'm not understanding how it happens. I would like to know more Yep... I watched that Julius Sumner Miller video on COM a few times... and it is calculated by averaging out things... so.... even if fellas are counterweighting a catamaran by hanging off the side of the boat... It can be said that all of the boat (and fellas) is still inside the boat. I think that one side weight on the right side could be very useful... maybe also half a side weight behind the axles on the left side. dunno anyone that really tested for this though... |
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Post by micro on Oct 9, 2017 12:18:29 GMT -5
The golden triangle is mainly used as a reference for keeping the raised wheel from bobbing up and down. Weight behind the axles does not fall within the golden triangle either... i have always considered areas not inside inside the golden triangle or inside the bizarro triangle as somewhat an unknown quantity. Correct, but how would the weight that is in front of the rear axle on the NDFW side act? That side would need to have a smaller wheel weight. One that is cut in half or a fourth to a third to prevent the weight from being on the front side of the triangle. That is where you don't want it I believe. I have not tested it, but that is what I would try first with the cub weights. I don't think that having a full cub weight on the the NDFW side is helping at all and would create more wiggle. Anyone ever just test with a cub weight on the DFW side only? Any results from that? |
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Tungsten
Oct 9, 2017 12:44:20 GMT -5
via mobile
Post by Professor Moriarty on Oct 9, 2017 12:44:20 GMT -5
Exactly...
It would want to be light in front of the axle on the left side of the car.
In that Sumner Miller video... he also showed how the center of gravity could be in a place where there is no car.
Imagine the D4D car...
Where would the COG be on that thing?
Yep... a similar area that our cars have the COG... even though there is no car body there.
I don’t know of anyone testing a car with only one side weight.
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Post by Professor Moriarty on Oct 9, 2017 14:21:28 GMT -5
Ya know... I am struggling to figure out this wobble thing too...
It seems to go completely against my understanding of the known universe...
Everything else seems to get tested ad nauseum in PWD...
Except for this idea. With this one it is like pulling teeth.
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Post by Professor Moriarty on Oct 9, 2017 15:45:00 GMT -5
Micro, it is customary in physics and in engineering to look at weight distribution and reduce it to the center of mass (CM). What this proven convention does is allow the simplification of equations. So by this convention, locating 2 oz one inch outside of each rear wheel is equal to a 4oz weight centered between each wheel. You do increase the moment of inertia in this plane, making it harder to rotate on the horizontal plane but CM is the same. As a good example of this effect, consider the pole a tight rope walker carries. By what is being described here, it would make him less stable. DISCLAIMER: I'm not saying this behavior does not happen, just saying I'm not understanding how it happens. I would like to know more Would it be possible to rig up a test similar to this one to gauge the "wobble effect" that wheel weights might (or might not) produce? Hold on! Wouldn’t the Thunderboard be able to record any pitch or yaw going on? |
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Tungsten
Oct 9, 2017 23:56:20 GMT -5
via mobile
Post by Bracketracer on Oct 9, 2017 23:56:20 GMT -5
Using the tight rope walker analogy here. If the pole was, say, 10 feet long and weighed 20 pounds bare and we slid two 10 pound weights together right in the middle and walked the rope and then slid each weight out to opposite ends and walked the rope again wouldn't the second setup be harder to start rotating BUT also be harder to STOP rotating once it got moving? So the oscillation may be slower but the amplitude could be higher for a given rotational force?
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Post by Bracketracer on Oct 11, 2017 12:16:31 GMT -5
HELLO? <tap><tap><tap> Hellllooooooo? Is this thing on?
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Post by Chuy on Oct 11, 2017 17:44:23 GMT -5
So, the first statement is correct. It would be harder to start and stop the motion of the higher moment of inertia (weight to the outside).
The second statement, it is opposite. The same force or energy would cause smaller and slower oscillation in the system with a higher moment of inertia.
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