Experimental Weights |

MoJo Racing
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Experimental Weights Feb 28, 2018 9:33:11 GMT -7 DerbyBoyz likes this

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Post by MoJo Racing on Feb 28, 2018 9:33:11 GMT -7

Feb 28, 2018 8:58:14 GMT -7 txchemist said:

I will try to advance this discussion to something north of 4th grade. At any point in time, we all marvel at how the top racers have maxed out and optimized everything there is to do on these cars, and then someone has a breakthrough and an entire new direction opens up. The answer to what an optimized wheel is changes with the technology so it is always changing. For every change you contemplate, you have both things that will improve, and things that will be worse. Two different builders can come to opposite conclusions when trying out a new method if they do not have the same underlying values for their variables. For this discussion, assume Skippy is not just lucky, but has the best unlimited as he holds the track record. What did he do to get such speed? The things that stand out from say an older unlimited are smaller wheels. In addition to smaller wheels, it looks like some weight is dropped lower on purpose. Let's chime in on some physics on these adjustments, and do they work on other cars? I have put my comments on small wheel with what I think were the main improvements and main problems with changing the wheel. How about some thought on what are the main things good and bad about dropping the weights in your opinion.

I'm out... I didn't make it past 4th grade

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Skywalker Racing
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Experimental Weights Feb 28, 2018 10:39:35 GMT -7 The Zeebzob and DerbyBoyz like this

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Post by Skywalker Racing on Feb 28, 2018 10:39:35 GMT -7

Could also be as simple as Sweet Spots are very thick and it looks better to sit it lower than higher. I've heard Zeeb say his wheelbase isn't always a calculated move, but based upon where he thinks it'll look best.

I think its funny how people analyze every single build tactic a top racer employs and assume they have some super-scientific rationale for doing so. lol.

Vitamin K
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Experimental Weights Feb 28, 2018 11:17:02 GMT -7 Crash Enburn, DerbyBoyz, and 3 more like this

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Post by Vitamin K on Feb 28, 2018 11:17:02 GMT -7

Feb 28, 2018 10:39:35 GMT -7 Skywalker Racing said:

Could also be as simple as Sweet Spots are very thick and it looks better to sit it lower than higher. I've heard Zeeb say his wheelbase isn't always a calculated move, but based upon where he thinks it'll look best.

I think its funny how people analyze every single build tactic a top racer employs and assume they have some super-scientific rationale for doing so. lol.

Shhhh!

It's important that we overthink this.

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Experimental Weights Feb 28, 2018 15:43:17 GMT -7 The Zeebzob, DerbyBoyz, and 1 more like this

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Post by Admin on Feb 28, 2018 15:43:17 GMT -7

I don't think lower positioned weights are faster. The wheels on Skippy's car are small, so all weight will appear low. He actually has the weight placed higher on the body. Ground the weight off the bottom not the top. The days of lower is better are now over. LOL

Admin Administrator Posts: 1,277	Experimental Weights Feb 28, 2018 15:48:54 GMT -7 DerbyBoyz and 'The Fonze' like this Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by Admin on Feb 28, 2018 15:48:54 GMT -7 Dang I forgot about the possible Venturi effect with the low hanging weights. Crap maybe lower is better.

txchemist
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Experimental Weights Feb 28, 2018 16:38:10 GMT -7

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Post by txchemist on Feb 28, 2018 16:38:10 GMT -7

On the flat, weight might be above rail, but in the curve he has added and angled off 3 little parts on both sides so the middle big weight can drop below the rail and not rub. A lot of work if the rail is not going to hit the ends. One possible advantage a low weight has is to accelerate longer through the curve.

Doesn't this look like angled end pieces down on the lower left?

B_Regal Racing
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Experimental Weights Feb 28, 2018 16:47:31 GMT -7

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Post by B_Regal Racing on Feb 28, 2018 16:47:31 GMT -7

Feb 28, 2018 15:48:54 GMT -7 Admin said:

Dang I forgot about the possible Venturi effect with the low hanging weights. Crap maybe lower is better.

Someone around here may have performed quite a number of experiments with lower hanging weights on fat-wheeled cars

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Thinkin'Bout Racin
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Experimental Weights Mar 7, 2018 16:54:46 GMT -7

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Post by Thinkin'Bout Racin on Mar 7, 2018 16:54:46 GMT -7

Ok, I apologize for my earlier post. I was just trying to inject a bit of humor. Those that have seen me post over at PDO know that I can overthink things. The humor was an attempt to lighten it up.

So on to the weights -

Pros: I see a lower center of gravity with a lessor tendency to roll off axis. This should contribute to a more stabile car. I believe this would be most apparent in the curved section, but should also help the whole track length. Especially if an adjacent lane has a wobble.

Cons: The cross sectional area of the car would be increased. This would result in an increased drag coefficient. That is unless I am missing something (see below).

I see some discussion about the Venturi effect. I know what a Venturi is, but have no idea how this effects a PWD car? Can anyone explain this to me?

I am also trying to grasp the concept of why the lower weight would accelerate longer off the curve. I thought the distance from the rear axle centerline to the COM of the rear weight would be the determining factor on this, not the height of the weight?

Last Edit: Mar 7, 2018 17:54:42 GMT -7 by Thinkin'Bout Racin

Crash Enburn Poll Group Lanterne Rouge Posts: 165	Experimental Weights Mar 8, 2018 10:47:23 GMT -7 Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by Crash Enburn on Mar 8, 2018 10:47:23 GMT -7 The short answer is that a weight that is low in the car actually falls further than a weight high on a car. Quick geometry will verify.
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Vitamin K
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Experimental Weights Mar 8, 2018 12:21:42 GMT -7

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Post by Vitamin K on Mar 8, 2018 12:21:42 GMT -7

Mar 8, 2018 10:47:23 GMT -7 Crash Enburn said:

The short answer is that a weight that is low in the car actually falls further than a weight high on a car. Quick geometry will verify.

Does it though? This could be a "duh" moment for me, but it seems like the actual falling distance should be the same, regardless of weight height placement.

txchemist NPWDRL Sponsor Posts: 92	Experimental Weights Mar 8, 2018 12:33:16 GMT -7 Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by txchemist on Mar 8, 2018 12:33:16 GMT -7 See interesting test from Randy Davis of Max-V www.maximum-velocity.com/pinewood-derby-blog/2014/01/120/ He concluded - no improvement, but the car does accelerate more
	Last Edit: Mar 8, 2018 12:35:28 GMT -7 by txchemist

Thinkin'Bout Racin
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Experimental Weights Mar 8, 2018 12:34:02 GMT -7

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Post by Thinkin'Bout Racin on Mar 8, 2018 12:34:02 GMT -7

Mar 8, 2018 10:47:23 GMT -7 Crash Enburn said:

The short answer is that a weight that is low in the car actually falls further than a weight high on a car. Quick geometry will verify.

Crash, thanks for the answer. However I was never good at math. I am more of a visual learner.

Help me understand if you can.

If we have 3 elevations, A (weight high in the car), B (final elevation once the car reaches the flat section), and C (weight low in the car).

The difference of elevation A and C will always remain constant, correct? This constant difference will remain consistent even when the car reaches the flat section of the track, correct?

So the weight falls the same distance does it not?

Upon thinking about this again, maybe what you are saying is that the low weight will fall a longer distance not a greater elevation change? Much like a shorter WB car is allowed to fall a longer distance before the car starts to transition? Or is it related to the position of the weight while on the ramp slope?

Upon edit: ok, so I was typing while the other responses posted. The link to Randy's test was very helpful. One thing I did not see was how long his track was. So we don't know if it had a long or short flat section?

Last Edit: Mar 8, 2018 12:42:20 GMT -7 by Thinkin'Bout Racin

Vitamin K
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Experimental Weights Mar 8, 2018 12:38:59 GMT -7

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Post by Vitamin K on Mar 8, 2018 12:38:59 GMT -7

Mar 8, 2018 12:33:16 GMT -7 txchemist said:

See interesting test from Randy Davis of Max-V
www.maximum-velocity.com/pinewood-derby-blog/2014/01/120/

He concluded - no improvement, but the car does accelerate more

Ah, I guess that makes sense. If the track were a perfect circular arc, you could theoretically extrapolate a weight height at which the weight wouldn't drop at all, simply rotate as the car moved.

Thinkin'Bout Racin Poll Group Posts: 159	Experimental Weights Mar 8, 2018 12:43:34 GMT -7 Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by Thinkin'Bout Racin on Mar 8, 2018 12:43:34 GMT -7 Ok, great discussion! Now can someone help me out with the "Venturi" effect?

Admin
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Experimental Weights Mar 8, 2018 14:09:16 GMT -7 5KidsRacing, B_Regal Racing, and 1 more like this

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Post by Admin on Mar 8, 2018 14:09:16 GMT -7

There is no Venturi effect. It was posted more for humor. Sometimes people will focus on irrelevant info instead of perfecting the basics. I'm all for good discussion, I love things that make me think. I love testing most of all. I will say don't take any ones word for anything. If you have the ability to test, TEST! What sounds correct in theory or looks correct on paper does not always translate into gains in PWD. The first few years of racing I didn't try a lot of things because of the "Already tried that, it doesn't work" When I started giving things a test for myself I found a lot of things that didn't work for others actually worked for me. Don't get sucked into the Venturi, Perfect the basics and then mess with the other stuff.

Mar 8, 2018 12:43:34 GMT -7 Thinkin'Bout Racin said:

Ok, great discussion! Now can someone help me out with the "Venturi" effect?

Experimental Weights

Post by MoJo Racing on Feb 28, 2018 9:33:11 GMT -7

Post by Skywalker Racing on Feb 28, 2018 10:39:35 GMT -7

Post by Vitamin K on Feb 28, 2018 11:17:02 GMT -7

Post by Admin on Feb 28, 2018 15:43:17 GMT -7

Post by Admin on Feb 28, 2018 15:48:54 GMT -7

Post by txchemist on Feb 28, 2018 16:38:10 GMT -7

Post by B_Regal Racing on Feb 28, 2018 16:47:31 GMT -7

Post by Thinkin'Bout Racin on Mar 7, 2018 16:54:46 GMT -7

Post by Crash Enburn on Mar 8, 2018 10:47:23 GMT -7

Post by Vitamin K on Mar 8, 2018 12:21:42 GMT -7

Post by txchemist on Mar 8, 2018 12:33:16 GMT -7

Post by Thinkin'Bout Racin on Mar 8, 2018 12:34:02 GMT -7

Post by Vitamin K on Mar 8, 2018 12:38:59 GMT -7

Post by Thinkin'Bout Racin on Mar 8, 2018 12:43:34 GMT -7

Post by Admin on Mar 8, 2018 14:09:16 GMT -7

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