Folks,
I got bored a few days ago while reading all the posts about tripods, regarding who does what, who has what, and who thinks what is best, so I decided to take a few moments, review a few of my old engineering texts and notes, and I decided to write a small application to illustrate what happens when you have a tripod, a tripod head, a camera, and if you are so inclined, a bag of rocks hanging beneath your tripod's central mounting plate, especially when you put all those pieces together. This base application is identified as a vertical stability application that uses stacked objects within the simple math. This application can be turned into an elaborate three dimensional application, but that avenue happens to be beyond the scope of what I am trying to illustrate for many non technical users, an upcoming workshop tool, and users that simply might not care. Again, I am just trying to illustrate a very simple idea, yet complete with minor complex calculations for the group to play with during the Holiday Season, or whenever you happen to get bored.
This application is an extremely simplistic two-dimensional center of gravity model that uses the object's weight and the object's height above grade level to determine the combined device's current center of gravity (COG), when you attach a tripod head, and a camera to the tripod. Grade level is identified as a flat plane that intersects the tip of each tripod nodal point, such as the tripod's pointed tips on a surveyor's tripod. This model should not be confused with calculating the combined object's center of mass. They are distinctly different ideas, and these two concepts are often confused, where many mistakenly consider the concepts to be one in the same, but strangely enough the combined object's center of mass can correlate to the combined object's center of gravity.
The model assumes the following:
1. the model is working in two dimensional space only;
2. the tripod leg's tipped points are equidistant from each other;
3. the center of gravity's projection is vertical and central throughout all stacked bodies;
4. the original datum point is considered to be the plane that runs through the tripod's tipped points.
The model is designed to do the following:
1. indicate the center of gravity for your tripod at a certain height above grade level;
2. indicate the revised center of gravity when you place your tripod head onto the tripod;
3. indicate the revised center of gravity when you place your camera onto the tripod head;
4. indicate the revised center of gravity when you use a bag of heavy objects suspended from your tripods center post, or not;
5. indicate the revised center of gravity when you move the bag of heavy objects in a vertical motion along the center of gravity's projection.
The model does not account for any of the following:
1. the tilt within the tripod's head;
2. the center of gravity's projection shift as the camera shifts off center;
3. the transfer of any object's weight in a lateral direction;
4. the weight of any lens attached to the camera body;
5. any three dimensional center of gravity aberrations.
So, think of the model this way, while using stacked boxes…
1. I have a flat table, and I place a box onto the flat table, where I measure the box's height and weight, and I calculate the box's natural center of gravity.
2. I find a second smaller box, and I measure the height of this box, fill the box with marbles, and weigh the smaller box.
3. I place, and centrally locate, this smaller box inside the original box.
4. I suspend the smaller box filled with marbles by a string above the floor of the original box.
5. I centrally locate the suspended box.
6. I measure the distance from the bottom of the original box to the bottom of the second smaller box filled with marbles.
7. I calculate the revised center of gravity for this combined entity of boxes and weights.
8. I find a third smaller box, and I measure the height of this box, and I weigh the smaller box.
9. I place, and centrally locate, this third smaller box on top of the original box.
10. I calculate the revised center of gravity for this combined entity of three boxes and weights.
11. I find a fourth smaller box, and I measure the height of this box, and I weigh the smaller box.
12. I calculate the revised center of gravity for this combination of four boxes and weights.
The three external boxes represent the tripod, the tripod head, the camera, and lastly the internal box of marbles represents the bag of rocks, suspended from the center of the tripod.
There are Four Factors that Affect Stability:
1. Center of Gravity: A lower center of gravity generates a more stabile object...
2. Support Base Stance: A wider stance produces a more stabile object...
3. Center of Gravity Projection: When this projection falls outside the support base, balance will be lost...
4. Weight: It is more difficult to move a heavier, more massive object, as per Newton's Second Law.
The model will illustrate what happens to the combined entity's center of gravity, when you modify the weight, and height of each item. So, if you think a heavier tripod will lower your center of gravity, check it out, or if you think that adding rocks to a bag will do the job just as effectively, check it out, or if you think that adding a heavier tripod head to your tripod will help, check it out.
As a side note, and if the Engineers within the group would like to take this model further and, or they find a basic error in my logic, please feel free to correct the application as you see fit, since it is not locked. I tried to break the model, where it seemed to work properly, but then again who knows until it happens. Have fun, and take a look at whether your assumptions are correct, or not…
jim k
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Originally Posted by jim kitchen
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