Aggressive COG limits

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AaronS
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Aggressive COG limits

Post by AaronS » Mon Mar 19, 2018 6:28 pm

Can anyone tell me how aggressive the COG can be on a 4 3/8" wheel base assuming car is properly tuned to railride? The pros run extended wheel base. Is that a determining factor for more aggressive COG?



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Vitamin K
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Re: Aggressive COG limits

Post by Vitamin K » Mon Mar 19, 2018 6:31 pm

The track matters too. Not only aluminum vs wood (the smoother the track, the more aggressive your CoG can be), but also the shape of the curve. The curve of a Besttrack is a lot more brutal than that of a Microwizard. A lot of cars come out of the transition with some serious waggles on the former.



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Re: Aggressive COG limits

Post by AaronS » Mon Mar 19, 2018 7:14 pm

Hi Vitamin K. Thank U for your input and valuable insights! Let's say we are on a best track. Decently set up with good seams. Rear is balanced left-right and aligned properly. 130.5g in rear and 12.5g on DFW with 4.5" of drift in 4', theoretically. Is that pushing limits for BSA stock materials? What could happen?



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Vitamin K
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Re: Aggressive COG limits

Post by Vitamin K » Tue Mar 20, 2018 6:42 am

AaronS wrote:
Mon Mar 19, 2018 7:14 pm
Hi Vitamin K. Thank U for your input and valuable insights! Let's say we are on a best track. Decently set up with good seams. Rear is balanced left-right and aligned properly. 130.5g in rear and 12.5g on DFW with 4.5" of drift in 4', theoretically. Is that pushing limits for BSA stock materials? What could happen?
On an aluminum track, this sounds very doable. Ideally you'd want a wheelbase a little longer than stock. Maybe 4.75 - 5" if rules permit.



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Re: Aggressive COG limits

Post by Speedster » Tue Mar 20, 2018 10:10 am

Aaron knew I was going to get in on this. I raced Team Aaron on March 10 on a 1 year old, 4 lane, 35' Best track, Champ timer, set up for my District race. Distance from start pin to timer is 29'10". Aaron is in a different District but our rules are almost the same. We must use slots and keep the stock wheelbase. Aaron has a CoG of 1/2" in front of the rear axle slot.
Here's the specs on my car that I built for testing purposes:
1/4" Hershey bar shape. CoG is 3/4" in front of rear axle slot.
Front weight - 23.08 grams, rear weight 118.63 grams
2 ounce tungsten block behind rear axle slot.
24.60 gram tungsten bar, 14.36 grams (3 - 1/4" tungsten cubes), and 1/16" , 3/8" tungsten cylinder in front of rear axle slot. Tungsten putty to bring it to weight
Rail rider, drift set for 2" in 3'.
Weather was too cold to take it to my track.
This car was recently built so I can easily move any weight any place. I will get a time on this car on my track as it is now and then change the CoG to 1/2" in front of rear axle slot and see what happens. I will report all the tests I do.
On our 1st run, Aaron beat my car by .004 seconds. The fastest time at the Regulation race was 2.55X set by the Pack leaders son on the Best track. A time of 3.01 by the same car on the 40' Freedom track. He won the District race. Aaron's car and my car both consistently turned a 2.53X but Aaron's car was faster.
A side Note. I inspected cars this year at a Pack using a beautiful Piantedosi wood track. A car had a 1/2" CoG and ran the track very smoothly. The car went on to take 2nd place at our District race.
Best Wishes for all you CoG enthusiasts.



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Re: Aggressive COG limits

Post by AaronS » Tue Mar 20, 2018 5:21 pm

Thank U Speedster. I am definitely curious to know your test results on moving COG to .50" in front of axle. I'm thinking you will be ahead of the our car in times.



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Re: Aggressive COG limits

Post by AaronS » Tue Mar 20, 2018 5:41 pm

Hi Vitamin K. I'm restricted to 4 3/8" wheelbase and using stock slots. Car ran 2.533, and 2.516 on a 35' best track with champ timer. No wiggles in those two runs. Aluminum track seems to be the track we are and will be using. Given the previous stats and measurements from the previous posts I gave, what are the COG limits for this particular car?



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Re: Aggressive COG limits

Post by whodathunkit » Tue Mar 20, 2018 8:37 pm

AaronS wrote:
Mon Mar 19, 2018 7:14 pm
Let's say we are on a best track. Decently set up with good seams. Rear is balanced left-right and aligned properly. 130.5g in rear and 12.5g on DFW with 4.5" of drift in 4', theoretically. Is that pushing limits for BSA stock materials? What could happen?
Theoretically your COG would half to be a little bit less then 1/2" for the 4 3/8'' wheel base car.
And your total weight on the DFW would be in the ounce range's of 0.44 to 0.45
0.44 ounces = 12.47379 grams.. & 0.45 ounces = 12.75729 grams.

What could happen ? well it's a race win or lose!
And given the numbers of 130.5g and 12.5g that's 143 = 5.04418 ounces.
As for pushing the limits on stock materials.. :scratching: how are weights stock when they are to be purchased separately.. from the car kit. ;)


What type of automobile can be spelled the same forwards & backwards?

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Re: Aggressive COG limits

Post by Vitamin K » Tue Mar 20, 2018 10:19 pm

AaronS wrote:
Tue Mar 20, 2018 5:41 pm
Hi Vitamin K. I'm restricted to 4 3/8" wheelbase and using stock slots. Car ran 2.533, and 2.516 on a 35' best track with champ timer. No wiggles in those two runs. Aluminum track seems to be the track we are and will be using. Given the previous stats and measurements from the previous posts I gave, what are the COG limits for this particular car?
I can't tell you what the CG limits are. I imagine you could push it pretty low, as long as you have enough steer on the car.



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Re: Aggressive COG limits

Post by AaronS » Thu Mar 22, 2018 6:32 pm

Thank U Vitamin K. More steer makes sense to keep rear weight sliding down track evenly. I measured the side force on the rail to find approximate pressure of DFW on rail. 1.5 g was the measurement I got with my hand held scale. I laid an aluminum yard stick on my tuning board where 1 5/8" is marked. Lined up to right side of inner track rail line on board. Next, a 7" thin plastic ruler was placed on top of that with the rail side edge of the ruler sticking out about 3mm. I placed a few coins measuring the combined weight of them, on top equidistant my spaced. I rolled the car in a number of test runs and noted any movement of the ruler with coins. Slowly decreased weight through all the test runs until I saw that the DFW was just beginning to move the plastic ruler inward ever so slightly 1 mm. I then measured the ruler with coins. Measured 8.2 g. Next made a 90deg jig to hold scale on its side at 90deg. Had to reset it a few times to zero it. Then applied jig with scale face to edge of ruler until ruler with coins began to move 1mm. I measured a 1.5g pressure on the DFW. Has anyone tried this or had success with anything similar?



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Re: Aggressive COG limits

Post by Speedster » Fri Mar 23, 2018 8:49 am

Aaron, with your brilliant mind and at the advanced level of your skill, you need a Best track. You really don't know if the car your Team built doesn't actually have more speed.
I'll be cheering for your Team in May.



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Re: Aggressive COG limits

Post by AaronS » Sat Mar 24, 2018 9:51 pm

Thank U Bill. If you only knew how flawed my memory is U may think differently! Anyway, a Best track would be great, but no where to set it up, and my wife would probably put the brakes on that one. It would be a great way to test my tuning. Thank U for all of your speed tips on COG and wheel bore prep. You were right on staging the car at the start pin. Tested alternate wheel positions and found out that placing DFW away from rail and left rear wheel away from rail with only daylight between other two wheels and rail, that there is only 7" of no rail contact. Centering the car gives 5" of no rail contact. Not really a noticeable gain of less friction. Car has to travel a longer path, so not worth it. Found a video that tests this very idea. There is a .001 sec loss for not centering g the car at the pin. Here is the youtube sight: https://youtu.be/fkDPKi_rr9E



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