Calculating Center of Gravity (COM)

[Sssnake]

I use the following formulas to calculate the CG of James' car. The results were:
CG along the wheelbase- .815" in front of rear axle
CG across the track- .075" off center to left
CG height above axles- .057" above axles(.0105 above center of rotation)
Drawing lines through these three points gives a true center of gravity at the point they intersect.

Center of Gravity above axles (point of contact with bore)

CGH - Center of Gravity Height
WB - Wheelbase (inches)
TW - Total weight (in pounds, oz's x .0625)
FW1 - Front weight LEVEL (in pounds, oz's x .0625)
FW2 - Front weight, w/rear RAISED (in pounds, oz's x .0625)
FWc - FW2 - FW1 (change in weights)
HT - Height raised (inches)
Adj - Adjacent side (see below)
Tan q - Tangent of angle (see below)



Center of Gravity along wheelbase (formula gives distance back from front axle)

Rw- rear weight

Center of Gravity across track (formula gives distance from outside left of track)

Rtw- total right side weight
Trw- track width out to out

Jamie

[Mood Swing Productions]

the answer is 4 isn't it? it has to be!!!!!!!!!!!!

[RacerX]

Oh no guys, looks like Stan Pope has hi-jacked Snake's account here on our board!!!!! Just Kidding!!!


Racer X

[WarpSpeedINC]

moodswngproduction said:

the answer is 4 isn't it? it has to be!!!!!!!!!!!!

I know it is!!! It has to be..... or is it 3 8/8ths!!!!!!

[slkrnsntracing]

moodswngproduction said:

the answer is 4 isn't it? it has to be!!!!!!!!!!!!

Here are my calculations!!
(1.7598666 X 6) / 2.6398 = 3.99999984847
Just kidding!!

I'm sure the formula works, but if I have to use it to make my car run faster, I'm in trouble.

[RAIL HUGGER]

SNAKE -THANKS FOR THE INFO IT WILL HELP WITH CAR COMPARISONS

[pineheadwidow]

OMG Math!!!!!!!!!!!!!!!!!!!!!!

Is it really THAT complicated?

[HyperDrive]

Wow,
I'm an engineer and that looks too involved even for me. I just find the COM for the weight I add figuring the body and wheels are light as possible and don't have as much effect as the weights do and let it go at that.

[psycaz]

I thought the answer was 64. Isn't that what Douglass Adams came up with?

[dsracing]

What I want to know is if this is going to be on the test? I'm getting sweaty palms already and it is smearing the ink!

[2FAST4U]

WELL alls I got to say is cut a hole out of the back of the car
get your wife's best stainless steel spoooon...
an grab some lead,YES LEAD, fire up the small propane torch and melt the lead and pour it in and if you are with in 1 - to 1 1/2 inches in front of the rear axle there is your center of gravity... ;D

Glenn

or what he said...

[Mr. Slick]

I must be overly sympathetic today. . . or bored.

I have posted and excel spreadsheet that does the calculations for you.

The weights are in OUNCES and distances are in INCHES.

There are two versions - one for interactive use in MS-InternetExplorer and another that is the raw spreadsheet for those who use FireFox or other browsers.

www.pwdracing.com/pwdrl.html

Enjoy!

[j2ce]

Mr.Slick,

Just an observation but the maximum wheel base that car can have is 5.8" is that not correct. If I'm correct we cannot place the axle holes at the 0" mark nor the 7" mark of the block of wood.

j²ce

[Mr. Slick]

You are to enter your own values . . I didn't put any data entry limits in it.

The values there are just some values that I was playing with when I saved it.

If someone wants to make it fancy I could post that version.

[scottc]

I am new to this level of car building. I have built cars that always have done well but when they get to the district they always seem to have lost that extra edge. So, I decided to look where the "PRO's" go.

Could you please explain these terms a little better for me?
FW2?
HT?

[beakerboysracing]

Scottc,
i wouldn't get hung up on all the calculus or what ever that is at the beginning of this thread unless you have an engineering degree. Most guys here on this board just kinda do common sense trial and error to get the cars to go fast. If you want to give some specs on your car such as com(center of mass- where the car balances), what type of wheels, what mods to wheels you have done, what type of axles and thier mods, raised wheel or 4 on the track, or maybe post a picture of your cars, all the guys on here will be glad to help you without turning your brain to mush trying to understand complicated formulas.
Let us know how we can help.
beakerboysracing

[scottc]

We make simple wedge designs. Nose being 1/4 inch thick back to the tail being 1.5 inches. I have a COG 1 inch infront of rear wheels which are 1 inch from rear of car. Front tires are mounted 1.75 from front of car. Car over all length is 7 inches. Total weight. 5 oz.

Axles are polished down to 5 microns. wheel are trued to 1.180 inches with a devaition of no more than .005 of an inch. wheel bores are .096 axles are. 085 wheels are balanced. wheel tread measures .328 with a deviation of no more than .005 measured from dots to edge on bsa wheels. Wheel bores are polished using plastic polish the with a chenille pipe cleaner with hobby lube. I fill the axles after they are mounted with hobby lube spin them for about 30 seconds with a dremel the repack until hubs are filled with lube. I get about 45 seconds of free spin when "flicked" with my finger. Car tracks straight over 10 feet.

Here is where I think things get messed up. Our pack track is 32 foot wood with 4 foot drop. District is a aluminum track measuring 48 feet. Our car wins at pack by atleast 2 car lengths. It pulls away right from the pin and never lets up. At district the other cars pull away from us at the pin and we just never have a chance. The flat spot we look like we are towing a boat behind us.

Is there diferent method to build the car for wood and metal track??

[Parrot Racing]

When I signed up for this board, they promised there wouldn't be any math.

Enrico