90 Centre of Mass

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mmajor2

mmajor2

Member
Posts
86
Location
Surrey
Hi all, im not too sure where to post this as im a fairly new member of this forum.

I have recently been set an assignmet at uni which involves looking at all the forces involved with the suspension set up of a car. Obviously as an avid land rover enthusiast i have chosen to conduct the project on my 90.

Part of the project requires me to identify the centre of mass both from the floor and lengthways along the car. I really dont have a clue where to find or how to calculate this infomation and was hopeing somebody could help.

I know its a bit of an odd one but perhaps somebody knows someone that might be able to help.

I look forward to hearing any suggestions!
Cheers
 
i am not going to sit and do the maths but vertically top of chassis ,lengthways under floor plates between seatbox and bulkhead
 
Would it not be worth ringing/e-mailing Land Rover, surely they will already have this information, I'm sure some bloke with a big calculator has already worked it out:rolleyes:. If you ask them nicely they may just give you all the information you need and save you some work. ;);););););)
 
An obvious way of finding the front to back point is to drive it onto a seesaw and balance it (provided the seesaw is balanced beforehand that is). Obviously the drivers weight will offset it slightly from where it would be without a driver though.

Another way is to weigh it under each wheel using the kind of scales they use at race tracks. You can probably work it out from the readings of the weight on each wheel.

For side to side you could jack it up to the tipping point. When it tips over you know the centre of gravity point has crossed the pivot point of the tyre on the ground. Obviously this is quite dangerous though and your landy will end up on its side or roof, so I wouldn't recommend doing that, especially to your landy. Do it to a crap car instead :D
 
Hi there, I know this is an old post but I was wondering if you may spare me 5 minutes of your time. I'm doing a final year project at University on the design of a roll cage for an all terrain vehicle....naturally a Land Rover :) I was wondering if you found anything conclusive on the center of mass? If so do you still have the relevant dimensions? Any response would be gratefully received :D
 
Louis_nutter said:
Hi there, I know this is an old post but I was wondering if you may spare me 5 minutes of your time. I'm doing a final year project at University on the design of a roll cage for an all terrain vehicle....naturally a Land Rover :) I was wondering if you found anything conclusive on the center of mass? If so do you still have the relevant dimensions? Any response would be gratefully received :D
Click to expand...
depends which engine is fitted ,some sit at rear of engine bay some at front
 
Haha, not sure if my Uni would accept my thesis of 'jus drivin em' :D It's not actually for a Defender but I thought it may point me in the right direction. I have a series II SWB, to further complicate it I have done a V8 conversion, but I am not including this within my analysis. If I could just find an approximate value for center of gravity height from the ground I'll be well away with calculation. I've been reading up on methods of finding the center of gravity, balancing, lifting each end to measure the weight on each wheel etc but I'm over 100 miles away from my Land Rover and not entirely sure my Mum would approve of a lifting experiment in her front garden! Anyone know any approximate values or points on the vehicle i could get measured...?
 
I've got 1 Ton shackles and 7.50 tyres, so I guess it's also a little different for mine. Again....not including in my report! I've just had a brainwave, it nearly killed me :p couldn't the center of gravity be calculated from roll over angles? Does anyone know where I could go about finding this for a SWB Series II?
 
If Your at uni shouldn't you work these thing out for your self and not crib of someone else.

Any way this is how you do it . Put scales under each wheel from the recorded weights you can work out the longitudinal and lateral position of the CG. Then elevate one end about 2 feet still on the scales what ever the height call this "B", then drop a plum line down from the previously worked out longitudinal CG and mark the floor. Now measure from this mark too the front wheel contact patch and call this distance "F" Now measure the wheel base along the floor not the vehicle and call this "L" Next add the 2 rear scales readings together and divide by the total of all four scales to give you the value of "F" which we will call "G"
Now it gets interesting calculate the angle that the car is tilted "O" divide "L" by "B" and using Trig find the sine of "O" Lastly measure the diameter of a wheel "R" and you have all the info to work out the CG height "H".

H = F / tan O - G / sin O + R

now go figure and stop being lazy or you won't learn anything.
 
Not knowing how to work out the c of g and the roll centres(just as critical) and being at uni isnt a good sign, thats basic btec first stuff:confused:
 
You sould be able to work out how to do it yourself by now, as said, it's basic enginering principles.

I assume you can do bending moment calculations involving point load and udl?

Things like the engine and axles could be considered as point loads, chassis and body work as udl, the whole thing is 'just' a beam.

Not 100% acccurate, but it will give you a reasonable idea of where the centre off mass is assuming you can't weigh the thing, if you can then Owl's method will be much more acccurate :)
 
Ok, thank you for the replies, I did however state that I had researched/understood this method of obtaining CG height. What I was looking for was a ball park figure from somebody that had already obtained experimental data from a method such as this, not being 'lazy', being constructive with the time I have to perform a stress analysis that has very little bearing on where I sourced an approximate CG height from. I can totally see why people are dissuaded from using forums, being the first actual discussion I have had has resulted in people calling me both lazy and incompetent. Why do you people feel it appropriate to talk down to somebody who was simply seeking friendly advice?! Rant over, thanks for trying to help, I guess....
 
Louis_nutter said:
Ok, thank you for the replies, I did however state that I had researched/understood this method of obtaining CG height. What I was looking for was a ball park figure from somebody that had already obtained experimental data from a method such as this, not being 'lazy', being constructive with the time I have to perform a stress analysis that has very little bearing on where I sourced an approximate CG height from. I can totally see why people are dissuaded from using forums, being the first actual discussion I have had has resulted in people calling me both lazy and incompetent. Why do you people feel it appropriate to talk down to somebody who was simply seeking friendly advice?! Rant over, thanks for trying to help, I guess....
Click to expand...
cheerio!
 
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