formula for center of gravity

[professor]

Hey people does anyone know the correct way(formula) to work out center of gravity. the race car people do it all the time to minimise roll overs on the track

I think it has something to do with weighing the rig then weighing the rig with rear wheels raised a set distance to see how much weight has been transfered.

Chad

[bigpat]

Racers do it to calculate load transfer rates when cornering, and to help tune the suspension, not to prevent the car rolling over....

Anyway, to do it, you need accurate scales under all 4 wheels($$$$$), and have to be able to raise the front and rear at least 2 feet of the ground to get the weight transfer.

"Mechanical way:"
If you were to pretend to "roll" your truck (attached to 2 straps or winch cables , one to pull it over, and one to stop it going over), at the point where it tries to actually tip, stabilise it, and measure the angle of lean from the outside edge of the tyres relative to the ground. Make a scaled drawing, and draw this angle line inwards from each side, and where they intersect, is the line of the longitudinal centre of gravity. Just scale it back up, and you'll have your C of G height.

Tech way:

To calculate longitudinal CG location, divide the rear axle weight by total vehicle weight, then multiply by the wheelbase measurement. The answer is the cg location back from the centreline of the front axle. Give this number, the term 'A'.

Raise the rear a certain height onto blocks(eg 600-800 mm)., and resit on scales.

Divide rear axle weight by total weight( as now shown on all 4 scales), then multiply by the wheelbase, as measured down from the hubs vertically to the ground ( this number should be shorter than the actual w/base length). The answer from this is now called 'B'.

Now calculate the angle between the vehicle and the ground.

Height of blocks divided by 'B', multplied by tan ( scientific calculator)
(eg 15.5 degrees). Call this angle $

Final step is to calculate the CG height.

Height = ('A' divided by tan $) minus ( 'B' divide by sin $ ) + hub height above the ground.

Just keep all your units consistent and you'll be fine.

As a comparision, our Formula Holdens ( Formula 4000) open wheelers had a C of G height of approx 100mm above the floor! with a 40/60 front to rear distribution.

I suspect a stock Patrol or Cruiser to be anywhere from 600-1000mm......

Hope this helps mate.

Cheers,

Pat

[DamTriton]

Something I was told a while ago was that for most vehicles it's at the point of the gearstick. Apparently uncannily accurate across vehicle sizes/types with 2 ppl on board.

[Bush65]

Chad,

You might find the calculator here useful www.jeepaholics.com/tech/cog/

[professor]

wow Thanks people there is alot to it!
This should keep me busy

[just cruizin']

At work we have a tilt table where we can chain down vechiles then lift on side until the wheels lift off the table.

I can get pretty scary watching a $1 million fire truck at huge angles, the last one went to over 24 degrees.

[droopypete]

At work we have a tilt table where we can chain down vechiles then lift on side until the wheels lift off the table.

I can get pretty scary watching a $1 million fire truck at huge angles, the last one went to over 24 degrees.

road trip
Peter.

[Wooders]

And if the spring rates/heights are adjustable? I'd guess it's a little more complicated

[just cruizin']

I'm just waiting to get setup to post pics and then I'll put some up

[Cossie]

how does wheelbase affect centre of gravity?

for example a LWB GQ vs SWB GQ? the height of the cente of gravity wouldnt change would it? just the exact position along the car?

does that make sense? what I'm getting at is a LWB would flop at the same angle as a SWB wouldnt it?

[Suspension Stuff]

I'd reckon they would flop on the same side angle or close but there are more variables. Shorties usually run softer coils and are a bit lighter so objects sitting higher in the vehicle have a slightly greater effect eg(you and passengers.)
Also if you put a wheel up a 3 foot mound on a LWB and a SWB the SWB will be on a more severe angle (more scarey). I hope this begins to answer your question.
Shane

[ljxtreem]

Formula for Low centre of gravity = Grinder


Cut Cut

Mock

[MQ080]

[quote="Geeky Jeepy man"]ROA Alarm System

I am in the process of developing a two-axis (X and Y) Roll Over Angle Alarm System for my Jeep. This system will monitor the dynamic angles on my Jeep and provide a warning when I am approaching predefined Roll Over Angles.

This effort is currently incomplete.

This ROA Alarm System will incorporate the following design functions and attributes.

* Provide the ability to monitor my Jeep’s dynamic angles.

* Enable the setting of individual roll over angle “trigger pointsâ€

[professor]

[quote="MQ080"][quote="Geeky Jeepy man"]ROA Alarm System

I am in the process of developing a two-axis (X and Y) Roll Over Angle Alarm System for my Jeep. This system will monitor the dynamic angles on my Jeep and provide a warning when I am approaching predefined Roll Over Angles.

This effort is currently incomplete.

This ROA Alarm System will incorporate the following design functions and attributes.

* Provide the ability to monitor my Jeep’s dynamic angles.

* Enable the setting of individual roll over angle “trigger pointsâ€

[just cruizin']

Hey Geeky Jeep,

How are you going to calculate your Dymanic angle, given that there are a lot of external forces that can effect roll over such as velocity, radius of curvature etc. Your 3 degrees of safety margin may not be enough, by the time you get to that angle you may not be able to do anything but hold on. I know our application is generally slow speed but it only takes one rock you didn't see or is bigger then it looked and then that audiable alarm is just another annoying thing while your stungling to undo the seat belt and not land on your head.

A great idea and I'm sure if you have enough brains ( unlike myself) you'll be able to incorporate these into your device. Under $100 would be great but I'm sure people will pay heaps more if they regularly push their vehicles to the edge.

[bigpat]

To answer Cozzes question whether LWB & SWB cars have the same centre of gravity height, it would be no.....

The LWB being longer, has more metal in the sides and roof, more glass, heavier rear seats etc. Not only would the centre of gravity be slightly higher, but would also be slightly further back, again, due to more metal of the longer wheelbase.

Being a LWB, it would suffer from less pitching from braking, and could climb a steeper hill as a SWB before toppling front over back.

[Suspension Stuff]

To answer Cozzes question whether LWB & SWB cars have the same centre of gravity height, it would be no.....

The LWB being longer, has more metal in the sides and roof, more glass, heavier rear seats etc. Not only would the centre of gravity be slightly higher, but would also be slightly further back, again, due to more metal of the longer wheelbase.

Being a LWB, it would suffer from less pitching from braking, and could climb a steeper hill as a SWB before toppling front over back.

prove it

[Zute]

MQ080, someone has thought of it. The Jap's. Pajeros, 4Runners and Rockys have tilt metres.

[twinnie]

MQ080, someone has thought of it. The Jap's. Pajeros, 4Runners and Rockys have tilt metres.

my pajero's tilt gauge goes to 45 degrees errr i think it'd be over by then

Matt

[ljxtreem]

Roll it a few times,
you soon learn the point at wich it goes


Mock

[bigpat]

Prove it...... I don't want to volunteer for that one, mate, unless I;m usin your truck!

If you drive both a LWB & SWB the same distance up an obstacle, the SWB chassis will be at a steeper angle than the LWB, purely because the LWB has a LONGER WHEELBASE! SO... a LWB can drive up steeper terrain than a shorty before goin' A over T...

Dynamically, a LWB is more stable than a SWB, as in has a lower Polar Moment of Inertia. Doin' engineering has it's advantages......

[Suspension Stuff]

The SWB itself might have a slightly lower centre of gravity. The extra seats and stuff in LWB also has extra chassis. I know that the extra chassis won't account for the seats/Roof but if you have softer coils which shorties do and if you have a driver and passenger which makes a bigger difference to the way the shorty leans compared to a LWB because of the heavier LWB in ratio to the weight of occupants. (Unless the centre of gravity is higher in the car then the person's centre of gravity sitting in the car)

Also usually people roll when the nose is up or down; again in the LWB's favour.
Also because a LWB is more capable offroad except when turning, the drivers in the SWB have to try harder.

Professor make sure someone sits in the car and you have your gear you usually carry in the car when you figure it all out.

Shane