Does using post length affect stability?

[Ken Nguyen]

Hi Eric,

Thanks for the math. A very good mathematical illustration for understanding the weight distribution of the sled.

 

Back to my previous post about the shortest sled.

Using the XCS sled as an example (it's a shortest sled available I've been known and used):

30lbs; 2" gimbal to the camera plate (can not be shorter dues to the clearance of the docking) = 240in-lbs

Replacing the TB-6 by a LCD monitor shaves you off about 3lbs.

Now, the sled has to be extended 2" (240/12=20")

This is what I meant, "short sled is heavier than long sled"; and I didn't mean to compare from one manufacture to another.

Thus for clarity, I want to restate that: for the same made of sled, the shorter sled the heavier with the same distance of the gimbal to the top stage.

 

I did not mention about the use of the weight distribution of accessories in this because I believe most or all of us KNEW this. It's a basic thing for balancing while keeping the sled as light as possible.

The weight distribution and the gimbal placement can done the same in short sled and long sled.

Ken.

[Eric Fletcher S.O.C.]

30lbs; 2" gimbal to the camera plate (can not be shorter dues to the clearance of the docking) = 240in-lbs

Replacing the TB-6 by a LCD monitor shaves you off about 3lbs.

Now, the sled has to be extended 2" (240/12=20")

This is what I meant, "short sled is heavier than long sled"; and I didn't mean to compare from one manufacture to another.

Thus for clarity, I want to restate that: for the same made of sled, the shorter sled the heavier with the same distance of the gimbal to the top stage.

 

well, first off your math is incorrect. 30lbs * 2" gimbal height = 60 in/lbs which you will never achieve, since you are not taking the cameras CG height into account.

 

The more important point for this conversation is Why would you keep the same gimbal to camera CG offset?

 

The if you had three inches above the gimbal that you could use you could lighten the sled by a few lbs and then raise the gimbal keeping the sled the length and not add weight

[Ken Nguyen]

30lbs; 2" gimbal to the camera plate (can not be shorter dues to the clearance of the docking) = 240in-lbs

Replacing the TB-6 by a LCD monitor shaves you off about 3lbs.

Now, the sled has to be extended 2" (240/12=20")

This is what I meant, "short sled is heavier than long sled"; and I didn't mean to compare from one manufacture to another.

Thus for clarity, I want to restate that: for the same made of sled, the shorter sled the heavier with the same distance of the gimbal to the top stage.

 

well, first off your math is incorrect. 30lbs * 2" gimbal height = 60 in/lbs which you will never achieve, since you are not taking the cameras CG height into account.

 

The more important point for this conversation is Why would you keep the same gimbal to camera CG offset?

 

The if you had three inches above the gimbal that you could use you could lighten the sled by a few lbs and then raise the gimbal keeping the sled the length and not add weight

Eric,

I wrote 30lbs; 2" gimbal to camera plate which following your equation model from your previous post.

I suggest you should read the post patiently and digest all the information as well as all of the previous related points.

That was from your example with the camera CG 5" from the base of the camera plate.

I assumed you know it; that's why I didn't type it down.

So, 2" down to the center of the gimbal axis gives a total of 7".

And, that why it is 240in-lbs. (hope it's clear now)

 

Why I want to keep my gimbal 2" from the camera plate? That's the space for the thickness of the docking ring and the docking clearance. And, this give me the most lightest weight of the whole sled+camera+battery(s)+accessories. We all need this for long hour operation, long duration oner shot, and heavy camera.

(I know you understand the point but you just don't want give up a fight without a few punches left)

Love that attitude, any way!

Ken.

[Eric Fletcher S.O.C.]

I wrote 30lbs; 2" gimbal to camera plate which following your equation model from your previous post.

I suggest you should read the post patiently and digest all the information as well as all of the previous related points.

That was from your example with the camera CG 5" from the base of the camera plate.

I assumed you know it; that's why I didn't type it down.

So, 2" down to the center of the gimbal axis gives a total of 7".

And, that why it is 240in-lbs. (hope it's clear now)

 

Why I want to keep my gimbal 2" from the camera plate? That's the space for the thickness of the docking ring and the docking clearance. And, this give me the most lightest weight of the whole sled+camera+battery(s)+accessories. We all need this for long hour operation, long duration oner shot, and heavy camera.

(I know you understand the point but you just don't want give up a fight without a few punches left)

Love that attitude, any way!

Ken.

 

 

Yet agin you get your math wrong 7"*30lbs=210in-lbs.....

 

For your math to work out you would need a camera 34.2857 lbs.

 

i have been reading the post's patiently, including all the errors.

[Ken Nguyen]

I wrote 30lbs; 2" gimbal to camera plate which following your equation model from your previous post.

I suggest you should read the post patiently and digest all the information as well as all of the previous related points.

That was from your example with the camera CG 5" from the base of the camera plate.

I assumed you know it; that's why I didn't type it down.

So, 2" down to the center of the gimbal axis gives a total of 7".

And, that why it is 240in-lbs. (hope it's clear now)

 

Why I want to keep my gimbal 2" from the camera plate? That's the space for the thickness of the docking ring and the docking clearance. And, this give me the most lightest weight of the whole sled+camera+battery(s)+accessories. We all need this for long hour operation, long duration oner shot, and heavy camera.

(I know you understand the point but you just don't want give up a fight without a few punches left)

Love that attitude, any way!

Ken.

 

 

Yet agin you get your math wrong 7"*30lbs=210in-lbs.....

 

For your math to work out you would need a camera 34.2857 lbs.

 

i have been reading the post's patiently, including all the errors.

Ahhh!, Eric,

This is a good punch, almost a KO.

I was wrong this time. My head wasn't clear while I was typing. was in a hurry, I didn't proof read my post.

Ok, the distance of camera CG to the bottom base of the top stage is 6" (as in your example)

Gimbal center axis to the bottom base top stage is 2".

30lbs camera x 8" = 240in-lbs, this is what I meant.

Any more punch? (refer the liquid one with ice!)

Ken.

[Colin Donahue]

Now you're asking me to go all math on you...

 

THIS IS A HYPOTHETICAL RIG

 

30lbs camera

6" high CG from camera baseplate (Film Camera)

5" to the gimbal centeroid

330 in-lbs of moment

 

For the rig to have neutral balance you need to have 330 in-lbs of Moment on the bottom of the rig

15 lbs base

330/15= 22" under the gimbal centeroid to the base CG

 

Now try that with the

 

30lbs camera

6" high CG from camera baseplate (Film Camera)

3" to the gimbal centeroid

270 in-lbs of moment

 

270/15=18" under the the gimbal centeroid to the base CG

 

Where you're getting confused is you're looking at the physical size of the base without taking mass and CG into account. Build the ultra's base out of Depleted Uranium or Tungsten and it will have a shorter post even though the base is "Smaller". Tabling the Monitor and running it at the base of the rig helps to get the CG lower, as does running the batteries under the base.

 

Did I answer your question?

 

Eric,

yes, you answered my question! Thank you for the example.

 

Colin