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PostPosted: May 13, 2011, 10:55 am 
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I was searching over on the UK Locost site for something else, when I ran across this interesting homemade tool to balance corner weights; http://www.locostbuilders.co.uk./viewth ... ssage=none
It basically uses a brake cylinder and pressure gauge on a lever. The lever was used to lift a corner just slightly from the inside top of the wheel. One would measure the pressure on the gauge as a relative pressure from corner to corner. That got me thinking about an other way to skin the cat.

Probably, this has been thought of before, so I make no claim to originality (unless someone is going to market it :wink:) I came up with this design using the torque wrench instead of the hydraulics. Most of us have a torque wrench. It should be either a beam, dial or digital style wrench. Preset click types would not lend themselves to this application.

Ideally the bumper would be at the same level as the bearing, but should be very close for government work. The error would be equal for all 4 corners so if you were just considering balance, then the actual weight numbers are not important.

The dimensions in the design are based on the length measurements of my torque wrench. Using these measurements, the actual weight would be 4x the measured torque. The calculations are:

Actual weight = (Tapp * Lo/Lw ) * (12”/6”)

Where Tapp = the measured vale on the wrench
Lw = Effective length of the wrench
Lo = Length from bearing to pivot in the wrench handle

So using the design as shown, for a value measure on the wrench of say 100 ft lbs would yield:

(100 * 35/17.5)*(12/6) =400#

You should adjust the lengths of your design a bit so that the needle on your beam wrench would read around 2/3 to ¾ full-scale at the heaviest expected corner measurement. If you want actual weights, you can then re-calculate measured values using your dimensions.

The lateral beam should be of 1-1/4 16ga tubing minimum to prevent bending; heavier if you intend to weigh heavier vehicles or increase the length of the arm. The vertical support beam could be made from telescoping tube and drilled for various wheel heights. The disclaimer is that I have not built one of these. I throw it out as an exercise and discussion.


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PostPosted: May 14, 2011, 4:39 pm 
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Interesting idea. An idea comes to mind from your drawing that eliminates -any- readout yet should give good results.

First know how much you weigh. The base of the vertical tube is as you have drawn it (with triangulation for stability). The horizontal beam is going to be used as an off center school yard see-saw.

Use a wide lever on your side of the see-saw and SIT various distances from the pivot point until you lift the tire and the see-saw is level. Measure the ratio of the distances from the pivot point (knowing your weight etc) and solve for the weight at the tire end.

A few things that have to be taken into consideration;

1. The extra torque applied from the longer end of the see-saw when you aren't sitting on it will influence the final reading and needs to be accounted for. But it will be a constant downward weight at the longer end over the no weight condition at the tire end. That could be measured once with a bathroom scale and used as a constant to be added to your weight/distance.

2. Use a real bearing at the pivot point to reduce friction.

3. I want a small royalty please. :lol:

The link you posted doesn't go directly to the article. :cry:

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PostPosted: October 16, 2012, 4:15 pm 
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I made this exact thing to measure corner weight on our Super Vees in 1975. I plan to make another for the Locost.
It worked well.
Paul

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PostPosted: October 16, 2012, 5:48 pm 
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The flaw I see is that the wheel is lifted such that the tire just clears the ground. Since tires distort about 0.3 - 0.5" with weight on them, the measured corner weight will be off by that fraction of an inch. As an example, say the corner weight is 300 lbs, the wheel rate is 150 lbs per inch, and you now raise the tire an additional 0.5" in an effort to measure that 300 lb value. The "reported" weight will be 300 lbs + 1/2 * 150 = 375 lbs. Also, because a car is like a four-legged table sitting on a mattress, raising one corner will increase the measured weight on the opposite corner.

I don't see any elegant way to get round using proper scales.

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PostPosted: October 16, 2012, 11:51 pm 
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Maybe I'm over simplifying this, but, if you remove that 1/2" of tire flex by adding more air to the tire. I dont think the additional air will add that much weight.

Walt


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PostPosted: October 17, 2012, 6:58 am 
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My solution was two cheap bath scales($18). I made a cradle that I placed between the two scales that has a offset that equals the height of a 2x4 to set the tire in. I then set the other 3 wheels on a 2x10 boards after leveling and shiming the garage floor. It worked will and was repeatable within +/_ 1.5 lbs. I can take a photo if anyone is interesrted. Dave W


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PostPosted: October 17, 2012, 7:04 am 
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davew wrote:
My solution was two cheap bath scales($18). I made a cradle that I placed between the two scales that has a offset that equals the height of a 2x4 to set the tire in. I then set the other 3 wheels on a 2x10 boards after leveling and shiming the garage floor. It worked will and was repeatable within +/_ 1.5 lbs. I can take a photo if anyone is interesrted. Dave W

Please do. A pic would be great. I take it you do one wheel at a time.

Evo

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PostPosted: October 18, 2012, 6:44 am 
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Evo
I'll take a photo tonite. Dave W


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PostPosted: October 18, 2012, 9:28 am 
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Interesting that this post sat for about a year, then became active again.

KB58, you are right that as you lift the measured wheel that ~1/2", you will see increasing weight. As Walt mentioned, overinflating the tires to reduce the tire compression will certainly minimize the effect. However, I'm not sure that the math you used is entirely accurate. As you point out, once you begin to lift the wheel you will begin to make some weight transfer. So I don't think that a simple wheel rate formula applies. I'm not disagreeing with your premise in principle. Maybe we could simply counteract this ~1/2" tire compression effect by placing the other 3 wheels on 1/2" plywood? Determining the correct thickness of plywood necessary to compensate for tire compression should be easy enough to determine. :cheers:

If you are using this torque wrench method as a relative balance tool and don't care about absolute numbers, it should work better than using nothing at all.

I did not build the device I originally posted about but played with the idea as an exercise to replace the wheel brake cylinder and pressure gauge. I did use a bathroom scale. I used a single scale that measures up to 396lbs. (not many bathroom scales read that high) The problem with using most digital bathroom scales is that you have to "prepare" the scale to read and then place weight on it, then look at the read-out. Difficult to do all this by yourself before the scale times out, but it can be done. My scale happened to be exactly 1-1/2" thick and was large enough to place a tire directly on it and still see the readout. So the non-reading tires were supported by three 2x12's 1-1/2" thick. The process was: Place the 3 other tires on the wood. Lift the corner to be measured. Initialize the scale to start the calibration process. then slowly drop the wheel on the scale and quickly note the reading. Lift the tire, and replace the scale with a 4th piece of 2x12 wood. Move on to the next corner and repeat as required.

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PostPosted: October 18, 2012, 11:02 am 
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You can blame me for kicking the topic back to life. I was looking for a "locost" solution to corner weighting and noticed the design above and said to myself...."that looks familiar". That design works well on a formula car where everything is pretty symmetrical. For a car that carries unbalanced loads on its wheels, I dont think you have the required resolution.

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PostPosted: October 18, 2012, 12:02 pm 
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Quote:
You can blame me for kicking the topic back to life.


No blame necessary Paul. Just strange to see it come back from the dead and get more discussion.

Glad to hear that the design works. I was pretty certain it would. As has been rumored, "Everything that can be invented has been invented." :cheers:

In my little world, I have a near 50/50 weight balance. Most traditionally built sevenesques are close to that. It should work relatively well to corner balance for those builders. I think that using the 1/2" (or so) plywood under the un-measured wheels should remove the error introduced by tire compression. this should help "other" build styles or to get more exacting weights.

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PostPosted: October 18, 2012, 12:08 pm 
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You can replace the tires with something that is more solid. Maybe angle iron that you bolt onto the wheel studs or perhaps plywood or metal circles.

It's not required but it's a good idea to be able to check this so you get your coilover adjustements right. If you bump something hard or have an offroad excursion it's a good idea to check after that too. Plus it helps you with tolerances on your suspension mounting points.

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PostPosted: October 19, 2012, 7:09 am 
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Here a shot of my el cheapo corner Wt set-up, which uses two bath scales and a tire cradle. This arrangement is a lot more accurate than using a single lever arm scale set-up when it comes to repeatability. But it does take time to move to each corner. I just set the three wheels on 2x10 spacer boards so the vehicle is level. Note that some of the boards have to be shimmed. My garage floor is sloped for drainage, like most, and required up to about ¼” in shims to get everything level. I would mark your garage floor “permanently” for the location of the leveling area and also the boards so they go in the right locations each time, as you move the scale from corner to corner. The steel pan is set so the elevation in the static position is roughly the same as the 2x4 boards. The cradle that the wheel/tire sets in has a rib on the underside to reinforce that flat pan area. You may also want to make it slightly larger than I did, if you see a need to corner Wt other lite vehicles with larger tires. Last thing is when adding the Wt of the driver, and possibly the passenger, if that is how it is mostly driven; is you notice that it is difficult to get the Wt placement in the same spot, if you have to remove it. I used water softening salt bags as ballast. So try to get the final vehicle corner weight set without removing the ballast. If you do re-stall the ballast it can easily affect your readings by 7 or 8 lbs. Last I would make a note in your build book as to what increase/decrease change you see with a full turn on the front/rear shock collars, case of a quick track side adjustment is needed. Dave W


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PostPosted: October 7, 2013, 9:05 am 
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Made one of the torque wrench scales yesterday. Did not adjust anything yet, but did pick up a front wheel and it read 75 foot pounds. Times 4 and that sounds about right.
I still dont think that this will have great resolution, but should be good enough to get a road car in the ballpark.

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PostPosted: October 7, 2013, 10:23 am 
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This would join the poor man's front end alignment tools? IE, fishing string, rulers and a pumb-bob or two?

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