Load cell weight distribution on rectangular shape instead of square

Question

I have built a simple scale using 4 so called 50kg load cells.

They are connected in a bridge and mounted on wooden feet of a square shaped box. All as a proof of concept which worked quite ok. The readings are all OK and deviation of +/- 2kg is totally acceptable for my project. I followed this discussion which also explains how the connection should be made properly using 4 cells.

How to get weight data from glass electronic bathroom scale sensors?

Now I want to keep the load cells on the feet but change the shape of the scale and instead of a square use a rectangle with the following sides.

In such a form a weight distribution will not be centered all the time. The object to be weighed can shift to the right or to the left.

• Will this affect the measurements in a negative way or will the HX711 controller still take care of it and show the correct results?
• Will the measurements still be correct using 4 cells? If not what would be the proper way of weighing a rectangular shaped load?
• Would it more appropriate to measure the load with 2 cells on the right and two cells on the left and then sum it up?

Answer 1

Newton's second law says that if a force acts on a mass, that mass will accelerate at a rate proportional to the force and inversely proportional to the mass.

All that means for your scale is that if you are not being accelerated up or down, the net vertical force on your body must be 0. Since your body has weight, and the net vertical force on your body is 0 (you aren't accelerating, are you? :) then the downward force must be balanced by an exactly equal upward force. That upward force is the sum of the upward forces exerted by each load cell. Their contributions may individually change depending on where you stand, but their sum must exactly equal your weight.

Note that we have said nothing about the placement of the cells! If your platform allows it, you could move one of the cells 6 (or 60 or 600) feet away from the the others, for instance. The total upward force must still be the same.

So the bottom line is:

F_lc1 + F_lc2 + F_lc3 + F_lc4 == your weight

no matter where you place the cells.