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what its the function of the droptime ?


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#1 Nelson Reis

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Posted 29 June 2013 - 03:48 PM

I was wondering what is exactly the function of the droptime so i can better ajust my rig to all my cameras , witch all have different weigths from dslr.5 lb to ENG 14 Lb . I know that the droptime for my setups are suppost to be from 3 to 4 actually 4 secs seems to work better for me ..just wondering whats the droptime function on a rig is ?
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#2 Victor Lazaro

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Posted 29 June 2013 - 05:10 PM

Hi Nelson,
A short drop (2 seconds) time allows the rig to come back to its default position quickly it is great for locked shots and fast pans.
A long drop time (4 seconds) allows you to avoid the pendulum effect when you start and stop walking. It's also useful if you have to do a drastic tilt up or down.
In a few words, finding your drop time is finding the right drop time between a static balance and pendulum. The average is said to be 3s. but each operator has his preference, you can also decide to change the drop time depending in the shot.
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#3 Alan Rencher

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Posted 29 June 2013 - 05:24 PM

That's kind of like asking, "What is the function of gravity." Read this book: http://www.amazon.co...y/dp/024082380X


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#4 Nelson Reis

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Posted 29 June 2013 - 07:00 PM

Thanks Victor, and also thank you Alan for the link, will definally get that book .
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#5 Victor Lazaro

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Posted 29 June 2013 - 07:23 PM

That book, and the EFP DVD http://www.steadicam...am_efp_dvd.html are a must have for any beginner operator. Then a workshop is a great idea in order to not start with bad instincts and ask all your unanswered questions.
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#6 Jerry Holway

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Posted 30 June 2013 - 05:52 PM

Droptime for an "average" compromise between balancing feedback (seeking vertical) and pendulum effects (when accelerating and decelerating) also depends on the length of the rig. For a short, handheld rig like a Merlin, a 1 second drop time might be in the normal range, and for a superpost rig, 4-6 seconds might be in the normal range.

 

When all the rigs were one length (so long ago), it was easier to compare what each operator's drop time actually meant in practice, now it's a bit harder to gauge.

 

Jerry


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#7 Eric Fletcher S.O.C.

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Posted 30 June 2013 - 06:42 PM

When all the rigs were one length (so long ago), it was easier to compare what each operator's drop time actually meant in practice, now it's a bit harder to gauge.

 

Actually no, Drop time is drop time, changing the length of the rig doesn't change the degrees per second the rig is moving. We measure the amount of time that it takes for the sled to travel 90 degrees (Horizontal to vertical) Length of the post doesn't change that.


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#8 Victor Lazaro

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Posted 30 June 2013 - 07:09 PM

I think what Jerry ment is that because you are using a longer post, it is easier to extend your drop time to operate. The measure is still done the same way (90 deg angle drop time), but the nominal, or most confortable drop time varies depending on the length. Not a physics variation, but a user preference variation.


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#9 Jerry Holway

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Posted 01 July 2013 - 08:20 AM

What I meant was what I said. That a 3 second drop time with a Meriin length rig is absurdly long (it's very neutral and tough to balance), and a 3 second drop time with a very long rig is absurdly bottom-heavy (hard to tilt, and very pendular when accelerating or decelerating).

 

To put it another way, get the same "feel" of bottom-heaviness from one radically different length rig to another, one has to change one's "normal" drop time. 

 

Anyone can prove this fact to themselves. Just Physics.


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#10 Alfeo Dixon SOC

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Posted 01 July 2013 - 05:53 PM

 

When all the rigs were one length (so long ago), it was easier to compare what each operator's drop time actually meant in practice, now it's a bit harder to gauge.

 
Actually no, Drop time is drop time, changing the length of the rig doesn't change the degrees per second the rig is moving. We measure the amount of time that it takes for the sled to travel 90 degrees (Horizontal to vertical) Length of the post doesn't change that.

 


Actually Eric, we measure the time and of distance traveled of the 90º segment of the circumference. That in fact does change with the length of a rig.


Edited by Alfeo Dixon, 01 July 2013 - 06:15 PM.

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#11 Eric Fletcher S.O.C.

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Posted 02 July 2013 - 12:33 AM

 

 

When all the rigs were one length (so long ago), it was easier to compare what each operator's drop time actually meant in practice, now it's a bit harder to gauge.

 
Actually no, Drop time is drop time, changing the length of the rig doesn't change the degrees per second the rig is moving. We measure the amount of time that it takes for the sled to travel 90 degrees (Horizontal to vertical) Length of the post doesn't change that.

 


Actually Eric, we measure the time and of distance traveled of the 90º segment of the circumference. That in fact does change with the length of a rig.

 

 

 

You really want to stick with that answer Alfeo?  We are measuring degrees per second which DOES NOT change with length. A 3 second drop is always 30 degrees per second, a 4 second drop is always 22.5 degrees per second no matter how long or short the post


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#12 steve wagner

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Posted 02 July 2013 - 05:26 AM

Imagine you have two rigs: One is 1/2 LB bottom heavy with bottom end of post 4 feet  below the gimbal. Second rig is 1 LB bottom heavy with bottom end of post 2 feet below gimbal. Both have equal 'feel' :  i.e. how much push-back torque you experience for a given angle off level, i.e. equal perceived 'bottom heaviness' But clearly the shorter one will have a faster drop time due to shorter pendulum length since period of a pendulum doesn't depend on mass, only length. Just another way to look at the physics.

Steve Wagner


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#13 Jerry Holway

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Posted 02 July 2013 - 08:02 AM

Eric, no one is arguing that 90 degrees is not 90 degrees, or three seconds is not three seconds. Or that if you divide one by the other you get some other result.

 

What we are all saying is that if a 3 second drop time for a normal rig is what you like (the feel, the compromise between being able to balance the rig and the pendular issues when moving about), then you will need to have a different drop time if the length of the rig changes a lot.

 

All "droptime" is is a rough measure of that feel, which was conveniently similar, and therefore a useful way of describing that feel, when all rigs were the basically the same length.

 

Change the length of the rig a bunch, and your "normal" droptime is no longer useful at predicting the rig's behavior.


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#14 William Demeritt

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Posted 02 July 2013 - 03:45 PM

Droptime was discovered in the 4th century BC in the ancient land of Lisigavia...

 

Sorry, even for a newbie thread, this question is not far from saying you've been a baker for a while, but you're wondering what the different heat settings on the oven do. 

 

In an attempt to reboot this thread, and perhaps salvage it for future generations of Mövi operators, here's an attempt to re-rail this discussion: 

 

Your steadicam sled functions as a rigid pendulum with a cantilever ballast at the opposite end of a rigid rod. The camera platform is ballast A, your steadicam base (planar or coplanar) is ballast B, and the gimbal is the fulcrum. Ballast A is x distance from the gimbal, and ballast B is y distance from the gimbal. 

 

Two objects on a lever are in balance when the forces are equal: Ax = By, that is A times x (mass of A times distance x) is equal to B times y (mass of B times distance y).

 

If your camera platform's distance from the gimbal is such that it is equal to the force of the sled base times distance from the gimbal, the sled is "neutral", much like the lever we just described above. 

 

So, to change this equilibrium we created, we have three options: change the distance of B to the fulcrum; change the distance of A to the fulcrum, or change the position of the fulcrum (thus changing both distances at the same time). 

 

When you extend your sled without moving the gimbal, you changed the distance of B to the fulcrum, or y. This will exceed the force on the other end of the lever. On our steadicam sled, you just went from neutral to "bottom heavy", which is how we generally operate. 

 

Now that the force exerted at B is greater than A, and the sled is bottom heavy, the time to travel 90 degrees from a horizontal, rigid sled to a vertical, rigid sled (or specifically, the time it takes to travel that rotation) is effectively "droptime". 

 

Most of the time, we position the fulcrum closer to A rather than extend the sled, because we like to have the gimbal as close to the lens as possible. This has a rapid effect on the bottom-heaviness of the system. If the gimbal is as high as we can go still allowing us to dock it, then we extend the sled to increase y specifically. 

 

So that's my explanation on "droptime" and how we can control it... now why. I generally operate with 3.5-4 seconds of droptime, and I actually do that in every setup, every sled length, even with low mode. I find that with my operating style, a higher droptime works best for me since I watch the horizon pretty obsessively anyway. If the sled moves, and the base is very bottom heavy (meaning quicker droptime), that means our pendulum base creates more force I have to fight. Instead of fighting potential roll and tilts as the sled moves, a shorter droptime means less force (B times y minus A times x = force during movement assuming sled is perfectly vertical). 

 

tl;dr - droptime is the speed at which a steadicam sled rolls from horizontal to vertical, thus illustrating the "bottom heaviness" of the sled and the likelihood of pendulum effect when operating and moving the sled. 

 

Anyway, that's my explanation. Perhaps it was constructive, or just further delayed me going to grab lunch... but there you go. 

 

...now let's never speak of this again. 


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#15 Ants Martin Vahur

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Posted 03 July 2013 - 03:05 AM

I totally agree with Jerry. I don't understand what's with this Eric's primal urge to pick on some people like this.
You both are right, but talking about slightly different things.
Now imagine a 100 feet long superpost. Yeah, I know it's not possible, but for the sake of argument- imagine! If it's droptime would be 3 seconds, then who on earth would be able to control that? Imagine, or calculate, if you're able cause I'm not, how much mass it produces!


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