Re: Need a dingus thingamabob....

>>>And just what would such a dingus be called?

thanks
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There are a variety of devices one can use depending on exactly what you are trying to measure...

I am thinking that you are thinking of a device that you hold in your hand and it measures the force you are pushing with. We have one of these in our lab, it's an old thing, nicely made and it even has a name that says what it is called engraved right on the dial.

Unfortunately, I can't remember what it is called...

Jon

Greg Nowell said:

I have several tripods of different makes and want to evaluate their resistance to tippi-ness. I don't want to pull on them as they are not all the same and it would be difficult to arrange to pull at the same height. It would be simpler to push. Jon maybe you can remember to read the name of the gizmo at work and let me know. We also had a link posted, in the thread, I'll take a look at that right now.

regards
Greg N

Greg:

A couple of comments...

- If done properly, pushing and pulling are the same and pulling is easier to do. All you need is a hanging scale.

- This is a simple statics problem and measurement is really not necessary. The force required to lift a leg off the ground and the distance and force required for it to become unstable are both easy to estimate using simple geometry.

For the force required to lift one leg, you need to know the distance from the ground to the point where you are applying the force (ie height), the horizonal projection of the legs on the ground (ie, how far the legs are spread) and the total weight.

Pictures maybe necessary but one can see that the tripod will be tippiest when pushing where a leg attaches, the distance on the opposite side is one half the spread of one leg.

So:

leg lifting force = 1/2 x weight x spread/height

The spread is the distance from the center of the tripod to the point end of the legs in the horizonal direction. The 1/2 comes from geometry. The height is where you push.

From this it is clear that the important factor is, for a given height, how widely spread the tripod is, the wider the better. A widely spread tripod also makes it stiffer.

The point at which the tripod actually becomes unstable is a bit more complicated....

Jon