"Before you can synthesize, you must analyze.. -- Milton E. Hamilton
an engineer who could not analyze a design on paper would not be an engineer. One need NOT have the thing in ones hands to be able to do an engineering evaluation of the design and the marketing claims. This is especially true of something as simple as a multi-legged camera support.
Do you think that a Civil Engineer has to build and test the bridge before they could make an evaluation of its strength, etc...???
The argument that one need have a hands on with this thing before pointing out that the marketing claims are exaggerated is simply non-sense.
Perhaps, if the marketing hype had been toned down a little bit, if the claims had been a little less ridiculous (the claim that it is much more stable than a tripod is laughably absurd), the product would not have been subjected to such ridicule..
Last edited by BradS; 12-Jun-2009 at 10:48.
Not true! the attitude in play is different.
Every member of the Flat Earth Society has experienced standing on "the earth", and so have tested it is some aspect.
What we are seeing here is more of a belief system or "faith" in the absence of any exposure, beyond imagination.
Regards
Bill
No, but he does have to have more than a verbal description of it from an post on an Internet forum.
I can inspect the design of an item as effectively as inspecting a specimen, but the design must include: A clear description of the application on which the design is based, the requirements of the design to support that application, and the calculations of the design that respond to those requirements. The final validation of the design, which is indeed done after construction, is to confirm that the application is indeed supported. These are validation and verification processes, about when forests are felled to write the books engineers study.
After all, even a bridge has more requirements than just not falling down.
Rick "a civil engineer" Denney
Are you able to analyze the specific claim that the four legged camera support is more stable than the three legged support? Are you able to make some reasonable assumptions and use standard definitions and methods to evaluate this claim? Or must we take this claim as fact because it was uttered?
Or, how about this....design a tripod. Now, add a leg to your design of exactly the same design as the other three...analyze the stability of both designs. What conclusion do you come to?
If you do the stability analysis, please post you analysis here...and let the defense rest.
Last edited by BradS; 12-Jun-2009 at 12:43. Reason: typo.
This is not a court case. There is no defense. You are on the defensive, or trying to put others on the defensive, but that's all.
I can see where a four-legged camera support would be useful in some applications (which is NOT the same thing as claiming the product is well-executed, a good value, or anything else that would require that I evaluate the product directly). On a soft surface, the legs sink into the dirt. As I said in my previous analysis, which I suppose you have forgotten, there will always be one leg loaded more or less than the other three with a four leg system. But that doesn't mean that the support will rock, it just means that leg has to deflect enough (or the dirt on which is sits) to absorb any potential movement.
The stated requirement was not that it prevented rocking, nor did I see a claim that it solved a problem with rocking. The claim was that it would not tip over as easily as three legs. You are basing your statement on the notion that three legs always define a plane, while four legs may not. You have not shown that this is actually demanded by the design conditions, and I submit that it is not. There are two things required of a camera support:
1. It has to keep the camera from falling to the ground, and
2. It must keep the camera still.
To fulfill the first requriement, the support has to prevent the camera from overbalancing the support and tipping over.
Tipping will occur with the sum vector of gravitational forces on the camera and support fall outside the polygon formed by where the legs meet the ground. A two-legged support with sharp feet always tips because it's nearly impossible to keep that vector exactly in line with the two feet. Stated another way, if a plumb bob from the center of gravity of the camera and support points outside the area enclosed by the feet, the tripod will tip over.
So, one way to prevent tipping is to keep the center of gravity inside the polygon formed by the feet. One can't always spread the feet, and in any case doing so puts the legs more in bending and therefore makes them less stiff. A four-legged support will prevent tipping with a narrower stance and more upright legs, because the closest tipping points are further away with a square than with a triangle.
The distance from the center of the polygon to its closest point (or tipping point) is the apothem. If you load a tripod off-balance, you know from experience that it's more likely to tip when the heavy side crosses the middle of a line between the feet, and one way to stabilize it is to rotate the heavy portion to line up with a foot. That narrower dimension is the apothem.
The apothem of a polygon is:
r cos (pi/n)
where r is the radius of the circle containing the points where the feet touch the ground, and n is the number of sides (feet). An equilateral triangle has an apothem one-half of the radius of the circle described by the feet. A square has an apothem 71% of that radius.
If the off-balance can be described by the distance from the center of gravity to the center of the circle, that distance has to go (.71/.5)=1.42 times as far to reach the nearest tipping point. That's the basis for the claim that it is more stable--it is harder to get a support with four legs to tip than a support with three legs, given the same stance. That is why most tables have four legs, even if they rock, because if you lean on the edge of a table with three legs, it's easy to find yourself on the floor with the table on its side beside you. You can also use a narrower stance with the same tipping distance, which will load the legs more in compression and less in bending.
If you put a four-legged table on a sandy beach, it won't rock. The reason is that the more heavily loaded leg (and there will always be one, even with three legs) will sink further into the sand until they all reach equilibrium. A camera support intended for use outdoors that has sharp feet will allow that sort of equilibrium even with four legs. A four-legged support intended for use indoors would need soft enough feet to allow that equilibrium, and fine enough controls of the attitude of the legs to get it close enough so that the rubber feet could do their thing.
I think it would be a lot easier outdoors on natural ground (except rock) using sharp feet. Remember who Bob said wanted this support: Nature photographers. These are the guys that use fairly light cameras with very heavy and long lenses and slender, light tripods.
To sum up, I don't think it's a stupid concept on the face of it as you have characterized. I don't think one can reject the design out of hand knowing no more than the one fact that it has four legs instead of three. Your insistence that four legs will always rock assumes (effectively) infinitely hard feet, an (effectively) infinitely hard surface, and the inability to make fine adjustments on the legs easily. With the compliance that all structures have, all it takes is the ability to adjust the legs finely enough so that the remaining tendency to rock is absorbed by the compliance of the system. With all due respect, you are assuming much more than I am.
By the way, stating on a public forum that an engineered product is poorly engineered, without having conducted a proper analysis of the design of the product, is a violation of engineering ethics in the states in which I'm registered.
Rick "thinking people who claim engineering expertise ought to act like engineers" Denney
It's interesting to note that pretty much everyone who has claimed that the quadrupod won't work has also made the often implicit assumption that it's going to behave exactly like a chair or table -- where the legs angles are fixed.
I agree about the "reinventing the tripod" business; that's clearly false, since it's not a tripod... but that's just marketing mumbo-jumbo. It won't matter much if the quadrupod falls short in the field.
A few people keep harping the idea that Novoflex is a relative newcomer (though they can't even spell Novoflex), and completely ignore the fact that all companies are newcomers at some point. Not having a reputation doesn't make them bad. Or good, for that matter. I'm sure someone will try out the quadrupod and see how well it holds up in the field, and then we'll get to see some actual feedback about things like build quality.
Well said.Rick "thinking people who claim engineering expertise ought to act like engineers" Denney
Rick,
you have twice addressed point #1 and I agree, four legs, properly adjusted on soft ground are less likely to tip over than three. However, you have not addressed point #2 which is precisely the point of contention.
A condition for stability is that the points defined by the leg tips all be in the same plane....and, I guess that the plane be tangent to the ground at those same points. Notice that this does not require the ground to be a plane!
Now, with four points arbitrarily positioned in space, any three will define a plane and the fourth may or may not be in that same plane. Thus, a tripod is ideal in terms of stability. Let us assume that the fourth point is "close" to being in the same plane. In this case, the platform will rock with small perturbations in the load forces applied. A strong wind, inserting a film holder for example. Your prior analysis applies here except we're not considering tipping over just shifting from one equilibrium state to another nearby state (in configuration space). In another case, suppose that all four points are perfectly co-planar and that all for points are tangent to the ground...but that the ground is unstable...in this case, a small perturbation in the support again gives rise to instability.
You have twice publicly accused me of ethics violations and this time followed it up with a back handed insult obviously directed to me. I have not as you say, stated that the product was poorly designed. Nor have I ever said it failed to meet the design requirements. Nor have I disparaged the design engineer nor any other person. The main point of my argument is and has been focused entirely upon the marketing claims. Please re-read my posts carefully and see if you do not agree.
What does the canon of ethics for professional engineers say about making personal attacks and accusations against another in a public forum? The first time you did it, I dismissed it. This is the second. If you wish to so accuse me then, please do it through the proper channels and according to the proper procedure. Even if you do not wish to do so, may I suggest that you refrain from the use of personal attacks as part of your argument. It is dishonorable and makes you look bad to people who can see what is going on.
While insults and personal attacks may strengthen your argument in the eyes of the un-educated, such tactics generally weaken your argument in the minds of more intelligent readers.
Last edited by BradS; 13-Jun-2009 at 12:52. Reason: typos
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