MOI

[Guest]

Hi fellas,

Have you seen this wonderful video by Julius Sumner Miller?

TX Chemist introduced it to me.

Many thanks TX Chemist.

https://www.youtube.com/watch?v=9e9ysnJA9qA

 

[Guest]

Now, with this video in mind I would like to direct your attention to the SS rules:

Street Stock Classifications

The Street Stock pinewood derby class will be made up of 2 internal classes: Pro and Amateur. The Amateur class will be for the newer builders and first time racers. Amateur racers can move to race with the pro class at any time they choose.

Car Body ( the wooden/material structure that holds the weight, axles and other add ons)/ Total Car Dimensions

Wheel Base : Any as long as wheels do not exceed the 7″ total length requirement
Total Car Height : Not to exceed 3″ inches…
Total Car Length : Not to exceed 7″ inches…
Total Car Width : Not to exceed 2-3/4″ inches…
Total Car Weight : Not to exceed 5.0 ounces (+.04) or 143 grams even measured on 1/10th digital scale

Additional materials maybe added as long as they meet the rules

Other types of materials may be used to construct your own body and/or frame
4 Axles & Wheels must be installed to the side of the car body directly across from one another / No more than a 45 degree angle

Track Center Rail Height : 1/4″ inch ( 7mm ) *
Track Center Rail Width : 1 5/8″ inches (4.2 cm) *

* Wheels must clear the outside to outside center rail width measurement

Axles

a. Minimum diameter .084
b. Axles must have a nail head

Wheels

BSA, Maximum Velocity, Awana, Pinecar

a. May be CnCed, lathed, polished and/or sanded to true the edge of tread, surface and circumference
b. The tread / contact surface must remain flat and parallel to the bore as humanly possible
c. No Angling, Reshaping, Canting, Round Crowning, Tapering, H-ing, V-ing, Dishing, the outside of the wheels and/or tread surface
d. Lettering must remain visible on the inside and outside of the wheel.
e. Wheel covers may be used only if entire wheel is visible
f. 7.50mm Minimum Tread Width
g. Wheels must weigh at least 2 grams and a wheel can be removed after the race to be weighed to confirm weight.
h. The wheels can be trued to get to the 2 gram weight but they are not to be cut down intentionally under the weight limit and use foreign material to bring it back to weight.

The following Modifications are not allowed

a. Starting or finish line devices
b. Electronic or lighting devices
c. Glass or extremely fragile parts
d. Paint that is wet, smudges or extremely sticky
e. Bearings and/or Bushings
f. Sharp objects, sandpaper or abrasives on the bottom of car (We do not want any damage to the rubber stopping pads)
g. Axles and/or wheels attached to any device that mechanically or alters rotation and spin
h. Any part of the car to go beyond the starting peg (see photo below)
j. Propellants

 

[Guest]

And now for the big question...

Is there a loophole somewhere in those rules that would allow for a big advantage.

From my viewpoint there is a huge gaping loophole.

A fellow builder disagrees which makes me think that the body snatchers have him.

The first builder to guess correctly will win the MOTM SS

Best of luck fellas!

 

[Guest]

Oh! and BASX

 

[Guest]

Go ahead fellas

Tell me I am wrong

I've been hearing that my whole life

La la la la la

 

[txchemist]

I channeled the ghost of Julius and asked your question

And now for the big question...

Is there a loophole somewhere in those rules that would allow for a big advantage.

From my viewpoint there is a huge gaping loophole.

and the answer is YES!!
Rule need to be modified, or contention will arise, however- some are doing a version of this that is an advantage to the present BSA wheel without totally pushing the limits of the rule- we are talking about lowering the moment of inertia.

 

[B_Regal Racing]

we are talking about lowering the moment of inertia.

Dang it. I was seriously hoping that everyone would think Laserman was a quack and this tidbit of information would be overlooked.

 

[B_Regal Racing]

Would not "G" under the modifications that are not allowed take of the MOI concern?

 

[The Iceman]

I didn't know OZ had a brother!! hmmm very interesting!!! Does he have anything on weight placement and fulcrums calculations for dummies?

 

[Crash Enburn]

Sorry, I'm not seeing the loophole. We are already thinning the treads from the inside, which takes away from the perimeter weight. The only thing (slightly) different here is that this video emphasizes the tread as being the place to lose the weight.

I haven't done it, not for lack of idea/knowledge, but for lack of machinery and skill set.

 

[txchemist]

Not changing the weight of the wheel.

 

[Guest]

we are talking about lowering the moment of inertia.

Dang it. I was seriously hoping that everyone would think Laserman was a quack and this tidbit of information would be overlooked.

Not a Quack BR,

But I did happen to take some pills that were not prescribed to me last night.

I started out on burgandy...

The LAST Army is officially disbanded

https://www.youtube.com/watch?v=1b2RUpzW6IM

 

[Peerless Racing]

Laser/Tx thanks for the great video. I have always considered moment of inertia when making my razors but they are closer to disks. The rules of our comp allow for any wheel modification I want. This is making me think that I need mass distribution closer to a sphere. If I'm following correctly mass is an independent variable when considering the potential energy consumed and the key factor is mass distribution. Do you agree

 

[Crash Enburn]

Not changing the weight of the wheel

Then I call shenanigans. The only way I can see to change the angular momentum, then, would be to cut the wheel and then use the removed bits to bring the wheel back up to weight...

*ding!* /images/boards/smilies/idea.gif

I see where you're coming from now. Seems that would be a PIA to balance.

And how could you reuse the removed bits without the addition of a foreign substance (like CA glue), anyway? And that would violate rule h: are not to be cut down intentionally under the weight limit, anyway.

 

[Peerless Racing]

The wheel can be trued to get the two gram weight all the video says is be thoughtful where you take the weight from.

 

[Peerless Racing]

And it only applies to people who make there own or can spec how they want there's made

 

[txchemist]

From and old post by 5 kids- he is taking the wheel down to a small diameter for the NDFW, but in the discussion it is clear one could start with the same old wheel and end up with a legal 2 gram full diameter with a thin wall and lower MOI.

 

[Peerless Racing]

Tx if I made razors would it be wise to load up the hub (outside with aluminum tape) to make the weight/mass more sphere like? What do you think

 

[Guest]

And it looks like TX Chemist wins the set of steak knives!

There was never a doubt in my mind it would be you TX Chemist.

Why stop at old BSA wheels though?

How about some Pinecar wheels? Or Max V?

Hey Peerless,

If you are making razors then the important thing isn't adding weight but removing it.

I sure wish I had a friend that could turn razors. Any takers?

 

[txchemist]

3M 421 Lead Foil Tape will get you there fast, but harder to balance.
sneaky trick- make a washer out of lead tape. cut wheel bore close to wheel, insert washer and glue back together & balance. Gets weight closer to axle. OR put tape on thin part of bore to be close to axle.

I do not claim this is legal for SS and BASX, just thinking out loud, and on razor wheels, they already approach the mechanical limit of low MOI vs weight, but who knows! Adding the weigh does start to move the MOI closer to center, but is increasing total mass which will slow you down.