Corner Weight Scales?

[MK1_Oz]

x4 = cheap corner weight scales?????????

http://www.ebay.com.au/itm/300kg-Electr ... Swll1WuT3M

[jpayne]

could work, but cheaper options
https://www.google.com.au/search?q=leve ... i2LJJaM%3A
or to prove they are a thing
http://www.ebay.com.au/itm/Corner-weigh ... SwGjpXTH~m

https://www.merlinmotorsport.co.uk/p/ad ... lbs-ada400

JP

[MK1_Oz]

Yeah I have already been down the hydraulic path. I concluded that ensuring the 4 scales are level and the cost of buying 4 gauges with sufficiently large dials to get an accurate reading meant it was not worth it. Not enough accuracy. Same with pieces of wood and bathroom scales me thinks. I have also looked at load cells but the electronics to make them work is out of my league!

[jpayne]

Only need one gauge!

JP

[MK1_Oz]

yes if you dont mind mucking around with multiple repositioning of the scale. Still thinking over options.....

[wayovermyhead]

After Corner weighing a number of different cars now with the proper gear, here are my thoughts.

To corner weight a car properly all four contact points must be perfectly level and true to each other, I generally set them up using a laser level. Even small differences can make quite a big difference in the corner values. I find it hard to believe that many of the online cheap methods such as using scales and planks etc could ever be accurate enough after seeing how much small differences can influence a reading. And if the whole process is not very accurate, really what's the point in doing it beyond just making educated guesses as to weight distribution in your car. If your car is built and all the movable masses (very few practically) are pretty well positioned within the car all your really doing is adjusting springs to create a better dynamic balance (mostly just for braking). it takes very little adjustment or level discrepancy to make a 20kg difference.... which is a big difference.

There are many other small setup things too like the fact that while setting up the car you end up raising it off and on the scales quite a few times, the suspension movement at the wheels creates quite a side load on the scales as it settles and the car wants to move around a bit too after repeated movements, I would question if a cheap set of scales is designed to take this sort of side loading and if the accuracy suffers.

I would only ever use a properly designed load cell plate like the commercially available corner scales. If I couldn't afford them, I'd just pay someone to do it for me. Anything less, and I wouldn't be confident I wasn't just wasting my time for what in practise could just be false gains.

Llew

[MK1_Oz]

Good comments Llew. I think some grease plates would take care of the side load and a cheap laser level to get everything lines up properly. Hear what you are saying though.

I assume the commercial corner weight scales come with adjustable feet to level things up? Given the cost of load cells I think the commercial manufacturers are having a laugh at our expense charging $2000+!!

[MK1_Oz]

Well after thinking and pondering I took the plunge and made a set of scales. I calibrated them with 15 20kg calibration masses (each correct to within 20g so total possible variance of 300g!!!).

They are based on 500kg load cells, an Arduino board, load cell amplifiers and a Bluetooth module that talks to an Andriod App that I wrote so that I could see the weights and percentage calculations easily. Accurate in 20kg increments all the way to 300kg (max masses I had available). Adjustable feet to ensure 100% level and even across the 4 plates. Well happy.

Tape square is where my new HAPP35 2 post hoist is going in this week!!! Great kit, go take a look www.happ.com.au

Scales.jpg (107.28 KiB) Viewed 10471 times

I finally got the lad to help me with weighing the car today. I wanted to calculate the centre of gravity height in order to put some accurate info into the brake calculation model that I have developed but I could not find a way of raising the rear of the car the minimum 26cm that I required given the car was sat up pn scales as it was. Will find some suitable wood and create a stable method another day!

These are the results I have. I am extremely disappointed that the car weighs 1,041kg with full fuel but no passengers. I was hoping this would be well under this figure. The pleasing thing is that the car appears to be very well balanced out of the box once the organic ballast is added;

Balance.jpg (24.06 KiB) Viewed 10471 times

If I could move 22kg from the front right to the front left then I would end up with an almost 50/50 weight split around the car :) Alas, there are not enough components to get anywhere near 22kg so I am stuck with it as is.

I need somebody knowledgeable in corner weighting to help me out here. By playing with the s'pension I can alter the corner weights. If I raise the ride height of the front left I will increase the weight on this wheel by X kg. Will that increase the weight on the rear right by X Kg also (or an amount proportional to the front/rear static split)? As corner weighting cannot influence the overall front/rear or left/right balance does this also mean that X Kg will come off the front right (and rear left)? By playing with the corner weights I will ruin the perfect L/R balance at the rear but I assume it is better to have the front axle balanced evenly than the rear??

Almost seems to me that it is not worth bothering with corner weighting.

Interested in your thoughts...

[wayovermyhead]

You have coil overs up back don't you? If so you should be able to get it pretty close all round. I personally wouldn't get too wrapped up in cross weights and trying to get everything perfect on paper, cause it'll do your head in. And on a tarmac rally car, will have no where near the useful effect as a really stiffly sprung track car on a nice flat race track. There is so much dynamic imbalance on a rally car in use that pretty close is really all is worth aiming for.
Having said that, I'd just try and get the fronts as even as possible first priority. Makes the biggest difference during braking on the limit, this is the biggest advantage by my opinion and would be of the most benefit on this type of car. Just work back from there making small adjustments as you get closer to where you want to be. The only other tip I'd give you is that while your logic seems right enough. Sometimes, logic doesn't come into it, and making an adjustment opposite to what you think will have the desired effect. Like I said..... you just gotta play around, you'll figure it out after a few hours... or more.

Good work by the way.

[MK1_Oz]

CheeRS