I have some measurements of a real life robot, and a 3d model of that robot (lets say in Unity) and I want to know the scale factor, plus I dont want to find the 3d models measurements and then divide with the real world ones to find the scale factor, in order not to get more confused with more mathematics than I am already. So, is there a methodology or will I have to do it as I mentioned?
You will have to do it as mentioned. However, if the 3D model is accurate, there is only one number you have to find. Choose any dimension you can measure on both the real robot and the 3D model.
Every matching real and 3D dimension will give you the same number for scale.
So once you calculate scale once, you can apply it everywhere.
If you know the Real dimension and want to calculate the 3D dimensions:
If you know the 3D dimension and want to know the real one:
This works for all dimensions. Note that angles don't change with scale. If something is 90 degrees at one scale, it will be 90 degrees at all other scales.
If you are measuring a mesh, then extremes are easier to measure than axis centers. For instance, in the following drawing, the 840mm dimension is probably the easiest to measure in your 3D model.