Weighing the van at home

[booster]

A while ago, I started a thread on the topic of benefits, or not, of using corner weights for our vans instead of axle weights. Lots of great comments.

http://www.classbforum.com/forums/f5...ghts-5994.html

The subject expanded into how a person could actually get the corner weights without paying a hefty price to a third party scale place, and Markopolo came up with a really clever way to do the weighing at home.

I had some time to play with stuff, so I decided to try to make the weighing easier and quicker, so it could be done just before leaving on a trip when fully loaded, for instance. I thought if it could be done in 30 minutes that would be quick enough.

I decided to use some home built weighing platforms that could either be driven onto by using lego blocks, or the van set on them with a floor jack. The discount steel place had some nice channel iron pieces that were two sizes bigger thicker than I wanted but they were 1/10th the price so I got them 12" by 20# structural channel. Picked up some drops of 2" black pipe at the same time.



One end has a full width piece of pipe for pivoting on when the other end is lifted.



The other end has two pieces of pipe with an opening in the middle for the lifting ram, that locates against the small angle between the pipe sections.



The center of the lifting ram is located exactly 20" from the pivot end center, and there is a mark made at exactly 10" from the pivot end. I put a stick on scale with the 10" on the 10" point of the support. With the scale in place, I will know exactly what my lift force ratio will be based on where along the scale the wheel center winds up. This makes it unnecessary to extremely accurately position the wheel on the support as within a 3-4" is no problem.



I am out of pics so continued on next post.

[booster]

I got a hydraulic pump for a porta-power type application from Northern, 10 to with a built in gauge, with the intent of changing the gauge range to what I needed at 1000 psi. As it turned out the gauge port was some totally off the wall thread that I couldn't get gauges for, so I had to tee in for a second gauge. I wish I had known this before, as I could have gotten the much cheaper 4 ton pump without gauge port instead.

Here is the pump and ram.



This is the ram with a piece of steel bar in the middle of the ram so it won't change lift location as it goes up and changes the angle slightly.



With the really unnecessary two gauges.



The ram slides in once the platform is in place and the van on it. Push in until it stops.

[booster]

Here is the van on the support. I did this off a jack in the garage just as a demo and the floor isn't level so not completely accurate, but shows how it works.



At this point you just pump up the ram to read and read the pressure on the gauge. I found to be accurate, you need to do it like taking blood pressure, by going past and then bleeding down until the pressure stops dropping. I just go up until the ram hits it's end of travel, which is indicated by the pressure rising quickly and pumping harder (careful not to overpressure gauge). This puts the support about 1/4" off the floor on the lift end. I open the valve a bit to bleed off oil at a moderately slow rate, and the pressure will drop for a while and then stop dropping with no change to the valve position. This is the pressure I use for the weight calculation. If I just leave it alone, the platform will continue to drop with the pressure staying the same until the pipe hits the floor, and then the pressure drops off toward zero. This makes getting the right pressure quite easy.

In this demo, the guage quit dropping at about 630psi.



With the platform back on the floor and the pressure noted, I then need to find the actual center of the wheel for the weight calculation. I built a pretty Rube Goldberg fixture that does all the stuff I need in one unit.

First I use it to locate the wheel center. The plastic pointer slides in and out for different hub styles.



I then use a homemade (from a big washer) plumb bob down through a hole in the center of the plastic pointer and move the sliding pointer until be washer lays right on the ruler attached to the platform. The measurement is taken at the center notch in the washer.

[booster]

Almost done, as now all that is needed is to plug the pressure and measurement into a simple formula to get the actual corner weight.

I have the formula on the center finder plumb bob doohicky so it is easy to remember.



So in this case, it is (45.2 times 630) then subtract 500, and then divide the result by 10.437 which comes out to 2680# on that corner.

I have two of the platforms made, so I can do one axle at a time. If I want better accuracy (by a very small amount) I can put the other end on legos.

Here is a picture of the wheel center finder, plumb bob contraption. The bullseye level makes it easier to keep all in line.



Repeat 4 times and we get all the information needed to know all the tire load. Side to side weight ratio, cross wedge weight, etc., all useful for handling issues. Good information to know if you are close on weight or tire loading, as one side could be overweight, but the average tire load could be OK.

[booster]

Here is a sample of weights that I got early on in the testing, before the plumb bob contraption. They did line up very well with our previous trips to the scales.

[booster]

As a sidebar. I think it would be very interesting to get some history on what is typical for corner weights on the various vans.

If anyone is interested and coming through the frozen (sometimes) northland, we will be happy to weigh your van if you would like. Just let me know and we will see how the timing works out, but we are retired and around most of the time except for trips. We are in the northern suburbs of Minneapolis, and have plenty of room and power to the driveway areas if you need to stay overnight.

[markopolo]

Wow, that takes it to the next level! It's so well thought out and built. It looks very safe to use. Also, very easy to use

I'm having trouble understanding the formula............

[booster]

The formula is hard to follow because I combined all the constants are ratios into combined constant numbers.

The 45.2 comes from the distances from the pivot, which would be 20" for the ram primarily for constants, and also puts in the conversion for area of the ram vs actual lift weight at the pressure. The minus 500 is an allowance for the fixture itself which gets weighed with the van. It weighs about 50# and is at 10" from the pivot.

I think this is where it would start

(20)times (P)times(2.26) = (10)times(50) + (W)times(D)

[markopolo]

Thanks, that helped a lot. I understand it now.

If I'm ever nearby I'll stop by & get the van weighed.

[scootertramp]

Hello Booster
I am intrigued by your ingenuity.
I live in Saint Paul, so I may take you up on the offer when I am done with my immediate modifications.

[booster]

That would be good, and a chance to see how a Dodge has the weight sitting. Just lit me know when you are ready to give it a try.