CoG calculation

[ianc]

I've been doing a little research to try to find out how I might determine my vehicle's CoG location so I can then work out how far my van can lean without tipping over. I've found this: http://www.jeepaholics.com/tech/cog/ which is pretty comprehensive but also a little scary with a 7.5 tonne truck.

Has anyone else managed to calculate this?

 

[charlieaarons]

There are formulae which calculate the height of your COG and from that the tipover angle by weighing each axle when level, and then weighing each axle when the ruck is tilted forwards or back at a precisely known angle. They are in the Mercedes bodybuilder files, Unimog for sure.
Can you get your truck weighed on a tilt table or with the front end blocked up and angle exactly measured?
https://bb-portal.mercedes-benz.com/portal/ar_mbs.html?&no_cache=1&L=en
Part A, section 4.4

Charlie

 

[ianc]

Charlie - I was hoping for a magic method that didn't require the blocking up I think I can get access to a set of weighing pads.

 

[LukeH]

You will chicken out before it tips, I can assure you. I had a coachbuilt Daily, very overweight and way taller than the Vario with heavy ply roof and topbox; I bottled before even getting close.
If you want to, make up a scale card cutout of the end of the van, stick pins in at the CoG points of your major items (water, gas, clothes, roof, walls, wheels, drivetrain etc. and hang little strings from them. As you tip the model you can see which contributors go beyond the outside wheel. You can then do the maths comparing what's inside with what's outside the pivoting wheel.
You will be greatly reassured.

 

[ianc]

Luke - How tall was that Daily? The Vario is 3.5m

 

[LukeH]

Your Vario is 3.5? Oh, I was basing that on Speed's Vario build (got a signed copy ) which says 3m. The Daily has a 2.2m x 5m heavy (you could have a party up there - we did) alu skinned marine ply roof 3.3 metres off the ground, with a huge top box full of truck tyres, bikes and window security grills bringing it up to 3.7m; so not that much taller than yours in fact, but much wider up top.

 

[graynomad]

Because you cannot accurately model the weight distribution of your rig AFAIK there is no way to know for sure without taking two readings as was mentioned above, or just tipping it over They used to use L-shaped tilt tables that tilted the vehicle until the weight came off one side and the vehicle rested on the "vertical" part of the L.

IIRC Doug Hackney did something in this regard...found it

http://www.hackneys.com/mitsu/index-CG.htm

I must read that again, I can't remember if he got a valid result.

All that said, unless you have cajones of steel you will never get close to the tipping point on purpose, I've seen double-decker buses at about 45 degrees and they still haven't fallen over. Still as a confidence thing it would be nice to know.

EDIT: Found it, who would have thought there'd be a youtube vid of a 50-year-old test

http://www.youtube.com/watch?v=C-fZA1NJtPA

Not quite 45 degrees but close.

 

[ianc]

GN - I remember seeing that London bus footage on TV. I'm guessing it much have been sometime in the seventies, because there were still using that bus type in Dublin at the time.

 

[graynomad]

The still use double-deckers in London don't they?

I used to got to school on similar buses in Sydney, they would shoot around negative-cambered corner at great speed, quite scary up on the top floor.