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Author: Subject: Height of Centre of gravity
Aled_g

posted on 5/11/09 at 02:12 PM Reply With Quote
Height of Centre of gravity

Does anyone know what the centre of gravity height is for a Locost roughly? very technical i know!
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alistairolsen

posted on 5/11/09 at 02:18 PM Reply With Quote
different for every car, Id guess about 5-6 inches from the base of the lower chassis rails through the crank, box and diff.

Wheels and brakes are blow this, bodywork, top end of engine and more than half the chassis are above it.





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steve m

posted on 5/11/09 at 02:27 PM Reply With Quote
I would of said marginly lower on my car 4-5 inches from the top of the bottom rail as with gearbox and diff diff on that mark, and 1/2 an engine above,
with out the engine there isnt much weight above the lower rails anyway

It would be intresting to actually find out, but how ?

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blakep82

posted on 5/11/09 at 02:31 PM Reply With Quote
i would say (as a complete guess) almost somewhere around the line of the crank/gearbox/prop. perhaps slightly above





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Breaker

posted on 5/11/09 at 02:40 PM Reply With Quote
quote:
Originally posted by steve m
It would be intresting to actually find out, but how ?


You can define the COG yourself by hanging your car up at 1 point. Then you should draw a (virtual) line from your "hanging" point vertically to the ground. This test should be repeated several times (f.e. hang your car by each wheel) and determine the virtual line. These lines should all cross in 1 point and this will be the COG.

Please post some pictures after doing this test

Apparently this is my 100th post !!!

[Edited on 5/11/09 by Breaker]

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dhutch

posted on 5/11/09 at 03:28 PM Reply With Quote
100posts? Get back to work.....

But no, i two would imagine it to be about where most have stated.
- Another way to work it out crudely would be measure the mass and location of the center of mass all key items, Engine/Gearbox, Diff, Chassis, etc and then calc.
- Although without a lot of work and attention to detial you could proberbly imagine simular to simular accruacy.

Another way to measure the hight of the CG if you have a set of scale (ideal four, that are fairly accurate) is to measure the corner weights of the car, then to raise one side (or the front/rear) 2ft or simular (a known amount anyway) and remeasure the corner wieghts. Then calculate your heart out.

Thats what they do at JCB for there diggers.


Daniel

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Breaker

posted on 5/11/09 at 03:34 PM Reply With Quote
quote:
Originally posted by dhutch
100posts? Get back to work.....

But no, i two would imagine it to be about where most have stated.
- Another way to work it out crudely would be measure the mass and location of the center of mass all key items, Engine/Gearbox, Diff, Chassis, etc and then calc.
- Although without a lot of work and attention to detial you could proberbly imagine simular to simular accruacy.

Another way to measure the hight of the CG if you have a set of scale (ideal four, that are fairly accurate) is to measure the corner weights of the car, then to raise one side (or the front/rear) 2ft or simular (a known amount anyway) and remeasure the corner wieghts. Then calculate your heart out.

Thats what they do at JCB for there diggers.


Daniel


Pfff, my empirical test is more accurate... Of course, if someone wants to calculate it; you can find the formula's here: Wikipedia linky

Enjoy !

[Edited on 5/11/09 by Breaker]

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Peteff

posted on 5/11/09 at 04:44 PM Reply With Quote
I don't know where it is, what baffles me is why anyone would want to know





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Macbeast

posted on 5/11/09 at 05:11 PM Reply With Quote
To design suspension for minimum roll ?





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Richard Quinn

posted on 5/11/09 at 05:39 PM Reply With Quote
I think mine's with all my 13mm sockets and 3mm allen keys somewhere in the garage. I'll find it one day!
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Bob C

posted on 5/11/09 at 05:55 PM Reply With Quote
balance the car on the 2 wheels of one side & take a photo from the front.
Do the same on the other side - take another photo.
Measure the angles with a protractor.
Seemples
Actually I've been meaning to do this with mine ever since I built it...... maybe one day ;^)

you need to know height of CG to work out your braking properly & if you want to calculate roll couples & stuff...


[Edited on 5/11/09 by Bob C]

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Cousin Cleotis

posted on 5/11/09 at 06:36 PM Reply With Quote
http://www.longacreracing.com/articles/art.asp?ARTID=22

Paul

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Confused but excited.

posted on 5/11/09 at 08:55 PM Reply With Quote



Pfff, my empirical test is more accurate... Of course, if someone wants to calculate it; you can find the formula's here: Wikipedia linky

Enjoy !

[Edited on 5/11/09 by Breaker]


I think you will find that that only applies to two Locosts orbitting about a fixed point in space and gives the centre of mass, not the C of G of one car.





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Steve Hignett

posted on 5/11/09 at 11:06 PM Reply With Quote
quote:
Originally posted by Aled_g
Does anyone know what the centre of gravity height is for a Locost roughly? very technical i know!


Do you actually want to learn what everyones Locost CofG is, or would you rather learn where the Roll Centre of each axis is of certain Locost' (type race cars for eg)?

[Edited on 5/11/09 by Steve Hignett]






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v8kid

posted on 6/11/09 at 02:42 AM Reply With Quote
300mm measured on my car using corner weight scales. I went to silly extremes to get it low so it might be a little higher on a "standard" locost
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procomp

posted on 6/11/09 at 07:34 AM Reply With Quote
Hi

It is in general quite a bit higher than most are thinking it is. And remeber that you have to include the drivers weight unless building a remote control version. And full roll cages espesialy the 45mm ones make a huge difference to the outcome.

Cheers Matt






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skinned knuckles

posted on 6/11/09 at 02:34 PM Reply With Quote
I'm with procomp on this one, cog is a hard one to call in a cr that weighs so little and the driver can make a massive difference.

are you looking at this from a racing point of view? what type of roll cage will you have? a full 4 leg cage will raise your GOG massively, a 2 leg not so much but still significant, how much do you wiegh? what size fuel tank will you have and how low can you get away with mounting it?

really every home built car, cobbled together from different parts and assembled for different porposes will have significantly different COGs. how long is a piece of string?





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kb58

posted on 6/11/09 at 09:16 PM Reply With Quote
Indeed. My tube frame, composite shell, mid-engine Mini was at 16" for CG.

One thing people need to keep in mind is that CG isn't about what stuff weighs, it's about where it's distributed. A plastic hollow model shell of a car that weighs 1kg has the same CG as one made of lead.





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