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Old April 17th, 2006, 10:28 AM   #1
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Question for Charles/Mikko/Terry and the gang

Hi all

I would like to clarify something with regards to rig stabilization.

On any sled system, is it more advantageous to have a longer post and balanced accordingly or a shorter post (also balanced) - what would each give you with regards to handling?

Not being an expert, my logical (I think) brain tells me that a longer post would bring about the bottom of the sled shooting out when you come to a stop - I think??

Sorry, for the basic question but I'm new to steadycam type rigs and want to get the basic correct.

Any help would be appreciated

Many thanks
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Old April 17th, 2006, 10:43 AM   #2
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The basic premise is one of weight and balance and how it relates to center of gravity. Borrowing from my pilot training, the further away from the center of gravity, the less weight is needed to bring about balance. Or, stated another way, the further away from CG you are, the less weight you need to affect the balance. In determining weight and balance for light aircraft, there is a reference datum that is the CG with all non removable equipment installed. Passengers, baggage, fuel, and engine oil are all calculated using the arm X moment from the reference datum. So, the longer posts on a stabilizer rig are essentially a tradeoff between usability and overall weight.

If you used a short post under the camera, more weight would be needed to balance the rig and would make it that much more difficult to hold up. So, a longer post is used with less weight. However, the post can't be so long that it drags the ground or becomes unwieldy to use, even though less weight would be required to balance the rig. Of course, the stabilizer rig isn't perfectly balanced or it wouldn't return to the vertical position when deflected. The idea is to bias the weight at the bottom to make the rig slowly (usually around 2 seconds) return from horizontal to vertical. The center of gravity should be the exact center of the yoke.

Hope this helps,

-gb-
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Old April 17th, 2006, 11:37 AM   #3
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Hi Greg

Thanks for the reply.

I have been able to balance the rig in both scenarios - both short post and long post without adding weight. This was achieved by moving the placement of the gimbal - hence my question.

I just want to hear from the experiences of steadycam type devices as to which option is the optimum - or is there any?
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Old April 17th, 2006, 12:27 PM   #4
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Jeremy:

Generally it is better to fly with a shorter post than an extended one. The reason for this is that the amount of intertia amongst the three axes is not distributed equally; the amount of mass that is displaced during a rotation in tilt versus pan indicates that there is much more intertia in the former. Thus it is good to limit the amount of this inertia by keeping the post shorter. This will result in a "faster" rig, i.e. more responsive, in that a diagonal move (pan/tilt combo) will be easier to achieve.

As far as the rig penduluming more with a long post, yes and no--the increased inertia will make it seem like it is doing this more because it is exerting more force and moving through a longer arc, but not in the same way as if you had added more weight at the bottom of the sled.

On a side note, it's best to avoid having too light a camera up top that requires one to slide the gimbal way down the post, the rig doesn't perform as well this way. Best to add weight to the camera to bring the gimbal back up, close to the camera.
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Old April 17th, 2006, 01:30 PM   #5
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Quote:
Originally Posted by Charles Papert
Jeremy:

Generally it is better to fly with a shorter post than an extended one. The reason for this is that the amount of intertia amongst the three axes is not distributed equally; the amount of mass that is displaced during a rotation in tilt versus pan indicates that there is much more intertia in the former. Thus it is good to limit the amount of this inertia by keeping the post shorter. This will result in a "faster" rig, i.e. more responsive, in that a diagonal move (pan/tilt combo) will be easier to achieve.
Aha - now that answers my question. What you say makes extreme sense.

Quote:
As far as the rig penduluming more with a long post, yes and no--the increased inertia will make it seem like it is doing this more because it is exerting more force and moving through a longer arc, but not in the same way as if you had added more weight at the bottom of the sled.

On a side note, it's best to avoid having too light a camera up top that requires one to slide the gimbal way down the post--the rig never performs as well as when the camera is close to the gimbal. Best to add weight to the camera to bring it back down.
I have had to add weight to the sled (my cam only being 2lbs) since the rig has been designed for for 5lbs and up. The reaon I bought it was so I CAN fly heavier cams in the future - but thats the future. At the moment I'm flying a Z1 for my own purposes. The gimbal at the moment is set very close to the sled.

I must also coin a phrase from another poster - I too have PROFOUND respect of you guys. This doesn't come easy but I refuse to give in and say its too diffucult.

I noticed that I had to move my butt forwards because the sled kept wanting to fly away from me. After a few minutes in the rig, I realised my Arny muscles are getting a decent workout for the first time in their lives - and a physio once told me sex was the best excersize for those muscles - but lets not go there!

Much appreciated you taking the time to advise on this one. I will become proficient and hopefully with advice from you fellows, I can become better in the end.

I will have to practise the basic moves to become proficient in that. What would you guys say is a good excersize regime?? Everyday for an hour or so or skip a day in between?

Again, many thanks
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Old April 17th, 2006, 03:53 PM   #6
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Jeremy, what rig are you using? Does it have an adjustment so you can change the angle of the arm, this adjustment will allow to you maintain correct posture without the sled flying away from you.

John.
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Old April 18th, 2006, 07:48 AM   #7
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Wow, I feel oblidged to respond to a thread with my name on it, but alas, all the good stuff has been said.

I will add that there is one other consideration when choosing a post length: As Charles noted, a longer post will no only 'push' the weights down, but also the camera *up* from the gimble. This can be used to your advantage if you want to raise the camera up higher. Somtimes you want a shot lookgin down from high up, teh solution is to add a lot of weight to the base, and then telescope the post up with a really light camera to get it up high.

Normally though it is in deed considered preferable to have a shorter post as noted, provided you can carry the wieght needed to do that - of course a lighter camera will need less wieght to balance it too - which is part of the beauty of the system and why the same idea works from the big Ultra all the way down to the Merlin for any camera!

- Mikko
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Old April 18th, 2006, 08:50 AM   #8
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Quote:
Originally Posted by John Steele
Jeremy, what rig are you using? Does it have an adjustment so you can change the angle of the arm, this adjustment will allow to you maintain correct posture without the sled flying away from you.

John.
Hi John

I am using the Aviator from Varizoom since this was what I could afford at our exchange rate.

Alas no, it does not have an adjustment but I have thought that one out myself and plan to mod accordingly. Just need to find the correct way of doing it without messing it up. An engineering shop will have to help out here but I don't consider myself an idiot with mechanical devices.

If anyone has ideas, a possible diagram on how to achieve this, I would appreciate it
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Old April 18th, 2006, 09:21 AM   #9
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Question for Charles/Mikko and the gang - V2

Quote:
Originally Posted by Mikko Wilson
Wow, I feel oblidged to respond to a thread with my name on it, but alas, all the good stuff has been said.

Normally though it is in deed considered preferable to have a shorter post as noted, provided you can carry the wieght needed to do that - of course a lighter camera will need less wieght to balance it too - which is part of the beauty of the system and why the same idea works from the big Ultra all the way down to the Merlin for any camera!

- Mikko
I feel good that you are obliged :)

Its nice to hear comments and opinions from different users in the field.

If I refer back to one of my previous posts, you did mention that a unit was available from Steadicam at the same price as to what I paid. However, after I called them telephonically, I was told I had to purchase via a dealer and no dealer I spoke to (telephonically) wanted to match the price for the used item! So i was forced to follow the route I did. And any other model in the range just put me over the top after throwing in the exchange rate (1:6 !!!).

So, I have the Aviator and even if it means me having to spend a bit more local dollars to achieve the ultimate. It will be a dang side cheaper than spending dollars - no offence to our US friends! I must add that I'm not sorry I bought it - if there are a few mods I have to do to make it better - I will. By the same token, it will make me one of the few operators in Cape Town (there are no registered SOC's in Cape Town) let alone rig operators that I am aware of. There aren't even any to rent!

I have already thought of a "spacer" cut at a slight angle to match the base of the connecting pin (where the arm connects to the vest) to angle the connecting pin slightly towards me - hence changing the angle of the arm and causing the arms and rig to be more "neutral".

If you have other ideas, they would be appreciated.
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Last edited by Jeremy Rochefort; April 18th, 2006 at 12:27 PM.
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Old April 19th, 2006, 12:14 AM   #10
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Jeremy,

Good questions and discussion. Sorry I couldn't get in earlier but I've been building.

I wish Charles had held off in giving his comments because when he speaks-that's it! What else needs to be said?!

From the pictures I have looked at of the Aviator I can't see where the arm hooks into the vest so exactly how to alter that angle is hard to tell. It sounds like you have a fairly good grasp of stabilizer principles and should be able to make some slight adjustment to bring the rig "in" a bit.

My added take on the longer post-shorter post thing is a longer post seems to get in my way more in that my legs can bump into the bottom plate easier. Everything can be overcome by practise but I like the shorter post best. I like it better as well because I can keep all the weights on the bottom plate which gives the rig more inertia and hence more stability. It makes the sled a bit heavier but the better picture is worth it. After all, that's what we're after right?

Tery
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Old April 20th, 2006, 02:07 PM   #11
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Quote:
Originally Posted by Charles Papert
On a side note, it's best to avoid having too light a camera up top that requires one to slide the gimbal way down the post--the rig never performs as well as when the camera is close to the gimbal. Best to add weight to the camera to bring it back down.
Hi Charles,

I was wondering if it was a typo to say that it is not good for the camera to be close to the gimbal? Because it seems to contradict with the rest of your statement (adding weight to the camera brings the camera closer to the gimbal, no?)

I am not sure if I am misunderstanding or not.

I am new to all this and am trying to learn as much as I can. I am a recent proud new owner of Terry's Ind!cam Pilot :)

I had a similar question as to whether it is better to have a heavier sled with the gimbal lower on the post or a lighter sled with the gimbal higher on the post. Or what is a good balance/ratio? What is a good general placement of the gimbal (i.e. 1/3 of the length of the post)?

Thanks!
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Old April 20th, 2006, 03:43 PM   #12
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Hi Peter,

Good place to ask questions to the best group of stabilizer users on the web. Mikko is a good one for info as well. There are others I could name but the list would be too long!

I'll be seeing Mikko next week.

Tery
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Old April 20th, 2006, 09:19 PM   #13
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Peter,

Thank you for drawing my attention to that--it wasn't clear, so I have reworded it in my original post.

There's no hard and fast ratio, but you shouldn't have more than three or four fingers worth of room above your gimbal, let's say that 3/4 of the post should be showing below the gimbal. If you like a more inert feel, add weight to the top and the bottom of the rig to beef up the load, maintaining the minimal amount of post above the gimbal.

One of the things that I find a little baffling about many DV-sized sleds out there, particularly the single section arm rigs, is that the camera almost always flies below eye level. On the big rigs we are able to slide in different length arm posts (that make the connection between arm and gimbal) to accomodate situations where you need to fly the camera higher, or lower. I admit to being a bit more intensive about this than some, as I have a total of 5 posts that give me a 24" offset in booming range, but I use all of them pretty regularly (my recent show with Jeff Goldblum forced me to regular mount the 18 inch "manmaker" to combat the 9" difference in our respective heights!)

I imagine this will be likely addressed in future generations of rigs, just as the adjustable pitch arm mount has been of late.
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Old April 20th, 2006, 10:13 PM   #14
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Thanks, Charles, for the clarification. Also, thank you for posting your clips on steadishots.org. Are there any clips of you at work (instead of showing the end result of your work)? That would be very educational :)

Also, can you explain the reasoning of why it is better for the weight side of the post to be longer than the camera side of the post?

I understand the reasoning of more weight = more inertia but if the system is balanced and the torques around the gimbal match, why does the length matter?

And does this mean, in your example, that when you utilize your "manmaker" posts, that you lengthen the bottom in proportion to the new height of the camera placement? How do you avoid kicking the post with our knees or getting tangled up in it?

Thanks for your kind replies,
Peter

Last edited by Peter Chung; April 21st, 2006 at 09:34 AM.
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Old April 21st, 2006, 01:07 AM   #15
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I can't think of the physics right now but the tactile sensation is such that it feels better to have the camera closer to your pivot point (gimbal). Also, the lens is that much closer to operating nodally, meaning that the further the camera mass is placed from the gimbal, the greater an arc it must make during tilts.

The extended arm posts simply elevate the position of the rig relative to the end of the arm. This shifts your usable boom range overall. I also use a J bracket that drops the position of the rig a few inches, which is helpful when shooting as low as possible in high mode.

Once one gets used to flying a Steadicam, it is very rare to knock into the sled, you gain a sort of 6th sense about its position and can maneuver it within an inch or two of your body without hitting it.
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