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Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Mon Apr 28, 2014 9:23 am
by Stan Pope
Speedster wrote:If rules dictate the stock wheelbase be used ( 4 3/8" ) and the wheelbase is shifted toward the rear (cut off the back 1/4" and move it to the front) ... Our rules do not prohibit this. However, if Stan's rule was implemented this would no longer be legal.
Actually, I think that the rule under consideration would explicitly allow this, depending on the exact limit distance imposed. As Speedster configures his car, the distance from the nose to the rear axles is approx. 6 3/8" and the distance from the rear to the front axles is less than 6 3/8", which would allow additional rear extension and possible use of more effective rear fenders.

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Mon Apr 28, 2014 12:05 pm
by Speedster
What am I not understanding? "The rule would limit the distance from each end of the car to the furthest axle to 6". My distance from the nose to the rear axles is 6 3/8". I would be illegal. I do not need anymore then 5/8" behind the rear axle. Anything beyond that I want up front. Extending the front of the car will change the position of the CM when it's sitting at the start line. Physics is on my side. Would a car designed this way under our rules be the best design for speed?

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Mon Apr 28, 2014 8:21 pm
by Stan Pope
Speedster wrote:What am I not understanding? "The rule would limit the distance from each end of the car to the furthest axle to 6". My distance from the nose to the rear axles is 6 3/8". I would be illegal. I do not need anymore then 5/8" behind the rear axle. Anything beyond that I want up front. Extending the front of the car will change the position of the CM when it's sitting at the start line. Physics is on my side. Would a car designed this way under our rules be the best design for speed?
Sorry ... I thought I recalled later leaving the measures open for setting after analysis. Yes, indeed if the limit were 6 inches, then it would restrict somewhat from your current technique. Should I interpret your comments to prefer a limit of 6-3/8" under the proposed rule?

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Mon Apr 28, 2014 8:45 pm
by Speedster
Yep, 6 - 3/8" would make me very happy. I am presently building a test car and one of the set ups will be with the 6 - 3/8". It will be interesting to see if that car happens to turn out to be the fastest.

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Mon Apr 28, 2014 9:10 pm
by Stan Pope
Speedster wrote:Yep, 6 - 3/8" would make me very happy. I am presently building a test car and one of the set ups will be with the 6 - 3/8". It will be interesting to see if that car happens to turn out to be the fastest.
What are your variables? What is your testing method?

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Tue Apr 29, 2014 5:03 am
by Speedster
I am building a 3 wheel RR using 1.8 oz and 2.0 oz tungsten blocks. These will be moved back and forth and side to side in as many positions as possible. I will then install 2 rows of 6, 1/4" tungsten cubes behind the rear axle slot, cut off the back and move it to the front. The tungsten blocks will be used in front of the rear axle. Front and rear cants will be slight because of our rules. 3 runs will be made for each set up on Lane #1 of my 30' track so I don't wear out the wheels. When this is accomplished I'll increase the cants to see if anything different happens. A vendors basic wheel will be used and Max-V's 4094 axles. I'm going to set the toe-in and get the highest speed possible on the 1st run and then leave it alone for the rest of the testing. A Micro Wizard timer and wood track will be used for the testing.
I'll post the results later this summer under a new Topic.
Any suggestions anyone?

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Tue Apr 29, 2014 9:11 am
by Stan Pope
Sounds like a pretty good plan.

Consider that the optimum DFW Toe-in varies with the fore-aft location of the CM, so NOT resetting the DFW toe-in may overstate the value of rearward CM location. How to avoid giving one particular CM Location an advantage? How to quantify the error in DFW Toe-in selection?

To quantify the error in DFW Toe-in selection:

Possible plan: Suppose you plan to make N runs to set DFW after each CM Location adjustment. With a car trial setup, make a series of 3*N timed test runs, recording times for each. Between test runs, tweak DFW Toe-in to try to improve time. Compare the times for run N and run 3*N. That would be the likely error. I'd consider doing this exercise several times to see the range and distribution of those likely errors. (Of course, follow a "relube" protocol, e.g. add graphite at the start of each case and "spin in" X times.)

To avoid giving one particular CM Location an advantage:

Before each test case, follow the DFW Setting procedure of N runs. Do it before each test case whether fore-aft CM Location changes or not, so as to avoid an error in the setting affecting a whole bunch of cases.

However, if one of your goals is to compare side-to-side variation in CM Location, use the same DFW Toe-in setting of all CM Locations that have the same fore-aft CM Location. (The reason is that the effect of side-to-side CM Loc changes is probably smaller than the effect of DFW Toe-in setting error and side-to-side CM Location changes SHOULD have the same optimal DFW Toe-in.)

A good way to document the CM Location is to record the weight on each wheel (if you have 3 scales on hand!) That can be backed up by weights of front and rear and balance point measurements. (The numbers should reconcile, easily done with a spreadsheet. If the spreadsheet reconciliation procedure doesn't seem so easy, drop me an email and I'll help.)

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Tue Apr 29, 2014 10:06 am
by Speedster
Stan, you do realize I'm 74 years old, the track is 30' long and another 5' on the brake track to retrieve the car. I'd like to accomplish this by the end of this summer. OK, I'm teasing. I have been blessed with excellent health. I know what you say is right. Anything worth doing is worth doing well. I do have 3 scales. I'll frequently refer to this Post. Thanks for your input.

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Tue Apr 29, 2014 1:22 pm
by Stan Pope
Speedster wrote:Stan, you do realize I'm 74 years old, the track is 30' long and another 5' on the brake track to retrieve the car. I'd like to accomplish this by the end of this summer. OK, I'm teasing. I have been blessed with excellent health. I know what you say is right. Anything worth doing is worth doing well. I do have 3 scales. I'll frequently refer to this Post. Thanks for your input.
Darn! Yer old! I'm a young thing ... 72!

Hmmm... time for us to recruit an apprentice! :)

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Tue Apr 29, 2014 2:22 pm
by Speedster
I suspect you already have many an Apprentice that has advanced to Journeyman from all your teachings over the years. You, and so many others, that explain things so we can understand it. A BIG THANKS to gpraceman for making it all possible.
Cheers,
Bill

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Tue Apr 29, 2014 2:33 pm
by Vitamin K
Stan Pope wrote:
Speedster wrote:Stan, you do realize I'm 74 years old, the track is 30' long and another 5' on the brake track to retrieve the car. I'd like to accomplish this by the end of this summer. OK, I'm teasing. I have been blessed with excellent health. I know what you say is right. Anything worth doing is worth doing well. I do have 3 scales. I'll frequently refer to this Post. Thanks for your input.
Darn! Yer old! I'm a young thing ... 72!

Hmmm... time for us to recruit an apprentice! :)
I hope I'm still playing with Pinewood Derby cars when I'm in my seventh decade. Keep rollin', guys. :thumbup:

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Sat Nov 22, 2014 3:03 pm
by DerbyAddicted
I have a different question regarding wheelbase length.

For a while (possibly forever), our pack has used stock wheelbase and required the use of the stock axle slots. Last year, w/o any input or approval from the committee, the new cubmaster assembled a new rule list. One of the rule changes was the addition of a maximum wheelbase of 4 3/4 inches.

This year, I was thinking of proposing we do away with wheelbase restrictions completely. But before I do that, are there any ramifications that I'm missing? ie is there a good reason to keep the wheelbase restricted?

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Sat Nov 22, 2014 7:18 pm
by Stan Pope
Vitamin K wrote:I hope I'm still playing with Pinewood Derby cars when I'm in my seventh decade. Keep rollin', guys. :thumbup:
Ummm ... Count 'em again! :)

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Sat Nov 22, 2014 7:22 pm
by Stan Pope
DerbyAddicted wrote:I have a different question regarding wheelbase length.

For a while (possibly forever), our pack has used stock wheelbase and required the use of the stock axle slots. Last year, w/o any input or approval from the committee, the new cubmaster assembled a new rule list. One of the rule changes was the addition of a maximum wheelbase of 4 3/4 inches.

This year, I was thinking of proposing we do away with wheelbase restrictions completely. But before I do that, are there any ramifications that I'm missing? ie is there a good reason to keep the wheelbase restricted?
Tradition is a strong motivator. Just ask Tevya.

Do your pack's cars (some or all) get to race in district and/or council races? If so, your pack should follow the rules that will be imposed there!

Re: Request for Analysis of Proposed Wheel Base Rule Change

Posted: Sat Nov 22, 2014 8:28 pm
by DerbyAddicted
Stan Pope wrote:
DerbyAddicted wrote:I have a different question regarding wheelbase length.

For a while (possibly forever), our pack has used stock wheelbase and required the use of the stock axle slots. Last year, w/o any input or approval from the committee, the new cubmaster assembled a new rule list. One of the rule changes was the addition of a maximum wheelbase of 4 3/4 inches.

This year, I was thinking of proposing we do away with wheelbase restrictions completely. But before I do that, are there any ramifications that I'm missing? ie is there a good reason to keep the wheelbase restricted?
Tradition is a strong motivator. Just ask Tevya.

Do your pack's cars (some or all) get to race in district and/or council races? If so, your pack should follow the rules that will be imposed there!
Agreed, but our District races are very informal, and are open to everyone so it's hard to use them as a basis for argument. So there's no downside to an unlimited wheelbase that I'm missing from an organizer's perspective?