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Old May 6th, 2003, 07:58 PM   #1
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Physics of Steadicam question

I realise that the full version of the Steadicam with the articulated arm and vest is a superb device for isolating body motion from being transmitted to the cam.

My question concerns the simple version - without the arm and vest.

In a walking shot scenario, the vertical motion of the centre of mass (the gimble) would have a cycloidal motion inherited from the operators body and slightly dampened by the operators arm (I see this motion in the background of steadicam footage ive seen)

To counteract this, has anybody placed a shock absorber (spring or fluid type properly calibrated) in the area of the sled pole between the gimble and the sleigh, in either a modification or a home made design?

If so what where the pitfalls if any?
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Old May 6th, 2003, 09:04 PM   #2
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Interesting question John.

The human arm does in fact have a tremendous ability to absorb the shock of walking or running when used with a handheld stabilizer, hence the proliferation of such devices. In fact, the original prototypes of the Steadicam (early 70's) were all handheld, some being horizontal poles and parallelograms and such. The primary reason for the arm and vest suspension was not to improve on the shock absorption capabilities but to transfer the weight of the system to reduce operator fatigue.

The "pogo" effect of the operator's vertical travel translating to the footage is largely variable by the operator's own skill. A handheld gimbal-type stabilizer should be accompanied by a solid handheld walking style, with slight knees bent and gliding movement to reduce the vertical travel as much as possible. The arm should then be able to take up the rest of the movement.

Generally, if "pogo-ing" is still present, it will be most noticeable if there are objects in the foreground (parallax). The background is usually the least affected by slight vertical movement.

As far as a shock absorber, having such a mechanism within the sled would present a myriad of problems, I believe. Chief of which is that the sled must be rigid to prevent vibration and unwanted motion, plus remain in a fixed state of balance. A more likely site for such a mechanism would be within the handle that attaches to the gimbal. This would mean added weight, bulk and cost to such a stabilizer, and I'm not really sure of the results.

Then again, it's always worth questioning these things, there may just be a better mousetrap out there!
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Old May 7th, 2003, 12:41 PM   #3
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Charles,

Your suggestion to incorporate damping in the handle or indeed replace the handle with a damper of suitable spring constant could be useful for the DV Steadicam type design (<)

Your comments on operator's skill, I feel, really hit the nail on the head.

I came across this years ago when several operators where called in to see if they could track the mortar line in a 30ft long wall, (a reasonable test) , the results were mixed and all exhibited the vertical pogo effect as you described.
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Old May 7th, 2003, 01:05 PM   #4
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That would have been a fun challenge--a "shoot-off" as it were.

At the Steadicam workshops, we routinely set up a length of twine stretched across the room and have the students track along it to get a feel for how to avoid that darn pogo effect.

Again, I would posit that given the right approach, it is possible to virtually eliminate this even with the current handheld versions (sans damper). It would seem that all of the shooters who traversed the dreaded mortar wall were likely unaware that they were allowing their vertical travel into the frame to such an extent.

For all those who are practicing and getting serious about shooting with their stabilizers, give this test a try!
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