1. Any support that is out of balance (the CG is not over the centroid of the feet positions) will load the legs differently. Yet many supports are stable and don't wobble even though loaded unequally. Clearly, then, equal loading is not necessary to prevent wobble. (I'm not saying that you are saying this--I'm just laying out some thinking.)
2. All structural systems deflect. That means that they are all compliant--the bits all deform (without damage, we hope) in response to a load. There is no material I know of that shows zero strain when under stress.
3. Natural ground does not form a plane at the scale relevant to this discussion.
4. If all the feet are in contact with the ground and carrying a load, the support will not wobble freely, though it may deform as load and balance varies.
5. But if the load does not shift, the stress on each component will not change, and therefore neither will the strain.
6. There are some transient loads on a camera, such as wind. Their effect will always be movement in the system. The requirement is to keep that movement below the circles of confusion at the image plane, just as we apply when considering, say, depth of field.
7. Thus, on a calm day, if all legs are in contact with the ground, there will be no movement, no matter how variously those legs are loaded.
8. On a windy day, the system will move, but this is as true with tripods and with supports of any number of legs above two.
9. The tricky bit is making sure all legs are in contact with the ground. And I think this is where you have hung your hat.
10. But (and this is the hook my hat is hanging on), since there is compliance in the system, all that is required to make sure all legs are in contact with the ground is sufficient adjustability so that the fourth leg can be made to touch the ground and carry a load within the range of the system compliance. I don't think this is all that hard to do, conceptually. I have nothing to say about execution, not having seen the product.
If you will note, I have stated only what I find in the ethics laws, and left it for you and others to examine your own statements. I have made no accusations, nor have I attempted to call into question any particular statement. I consider it defining a boundary, as I see it, and leaving it for each person using his engineering credentials to analyze the product to decide for themselves where they are in relation to that boundary. In a court, statements made by someone claiming to be an engineer that could be shown to have caused financial harm to a product maker without making a proper analysis, could be subject to a complaint. Highly unlikely, of course, but it does happen--just read the engineering board newsletters.
(Obviously, I am not accusing you of ethics violations. To do so, I would have to connect your specific behavior with a specific ethics clause, which I have not done. Think of it as, "Be careful, in some states that could construed as..." which is not in any way an accusation, nor do I mean you any animosity at all. As to what others think, or whether it strengthens or weakens an argument--that is not my concern. Most others who are still reading this should decide to evaluate the product for themselves, which is exactly my recommendation)
Rick "very careful about language when signing as an engineer" Denney
Bookmarks