Wheights for pilot & Xh-A1

[Sam Morgan Moore]

BTW it is probably best with the Pilot to slide the whole lower spar rather than move the battery

 

Interesting - again one is locking down the variables to the minimum of two

 

S

[Eric Fletcher S.O.C.]

In a perfect world the monitor would be at the bottom of the sled as is the battery.

 

Bottom line, all you need to do is start off with the sled balanced. I'm not sure if Baer-Bel still sells the "Micky" but that's exactly what it's for.

 

I always have my sled configured the same and since the sled is in balance it's easy to achieve dynamic balance. Same goes for lowmode, Since I know where things go to keep the sled in balance I can get the rig into dynamic with little to no effort.

 

Here's my method of Dynamic Balance that works very well for me.

 

Balance the rig statically as normal.

Set your drop time.

Now tilt your rig 90 Degrees like when you do for a drop test. Pan the rig 90 degrees so the battery rack and monitor are horizontal. Now do a drop test.

If the rig rolls to Monitor side move the batteries out or the monitor in. If the rig rolls to the Battery rack side move the monitor out or batteries in. Retrim for headroom and do another Panned drop test.

When you get it to drop flat, spin it... It should be dynamic

[Jerry Holway]

Sam-

 

Eric's method (and "the Mickey") only work if the monitor and battery c.g.'s are on the same plane.

 

Raise the monitor up from the battery (as most of us do to see the monitor better) and it does not work. The more the monitor is raised, the less useful the technique is for dynamic balance.

 

It is, however, a very fine way to achieve static balance (monitor raised or not), which is extermely critical for dynamic balance.

 

IF the monitor is low, it will also put your rig in or close to dynamic balance.

 

Otherwise, there is plenty of information here in the archives on dynamic balance....

 

BTW, Ted used this method of static balancing long ago, he wanted it in the EFP tape back in 1990, as a combo drop time and side to side balance all in one... but I said it was too confusing for a beginning tape, i.e., take it one step at a time..

 

So for the Pilot, with monitor up from the battery, the camera's c.g. will be to the rear of the centerline. Probably not very much, and less the longer the central post is telescoped. I'm guessing in the 1/4" to 1/2" range.... Guessing.

 

A potential problem with moving the monitor and battery together is that you are changing two things at once, rather than the classic method of achieving dynamic balance, which is to put the monitor where it belongs, and then discover the battery and camera positions by trial and error.

 

Jerry

[Eric Fletcher S.O.C.]

Eric's method (and "the Mickey") only work if the monitor and battery c.g.'s are on the same plane.

 

Raise the monitor up from the battery (as most of us do to see the monitor better) and it does not work. The more the monitor is raised, the less useful the technique is for dynamic balance.

 

It is, however, a very fine way to achieve static balance (monitor raised or not), which is extermely critical for dynamic balance.

 

IF the monitor is low, it will also put your rig in or close to dynamic balance.

 

 

Jerry, First off I prefaced my post with "In a perfect world the monitor would be as low as possible". Secondly, with my rig and my setup it works perfectly everytime. Thirdly you and I disagree on this everytime, BUT it does work and it will work even with the monitor raised.

[Sam Morgan Moore]

So for the Pilot, with monitor up from the battery, the camera's c.g. will be to the rear of the centerline. Probably not very much, and less the longer the central post is telescoped. I'm guessing in the 1/4" to 1/2" range.... Guessing.

 

Thanks all for the input

 

My 5mm start point is fair then

 

I think considering that the Pilot with three or so wieghts attached to the bottom (wich are in DB alone) the battery/monitors contribution to the overall stability is fairly minimal - the amount may be even less than 5mm

 

Honestly as a newb I am not sure I could even spin a perfectly set up rig flat !

 

In terms of the side drop test method I, as a newb, guess this 'theoretically' does not work but may/does work in practice with many rigs - hence the debate

 

S

[Charles Papert]

As you can see, DB has a certain amount of voodoo involved in that there are various different (sometimes conflicting) ways to achieve the same goal. A flat spin is a flat spin, so however you get there is good.

 

It's also worth mentioning that there are a number of very good operators who never, ever test their rig for dynamic balance, believe it or not.

[Sam Morgan Moore]

It's also worth mentioning that there are a number of very good operators who never, ever test their rig for dynamic balance, believe it or not.

 

It is my guess ,my only experience of heavier rigs being a V25 with a weight cage, and also my pilot with ex1+letus steel rails (bottomed out big time) that the natural inertia of such masses possibbly makes it less critical especially when partnered with years of operating skill

 

My experience of the the ultralight merlin sugests that with such a small rig it is easy to configure in a manner that is wildly out - the pilot less so and, I guess, a large rig even less so -possibly the reason GB managed to invent the system without, AFAIK, full knowlege of the subject

 

S

[Dave Gish]

I think considering that the Pilot with three or so wieghts attached to the bottom (wich are in DB alone) the battery/monitors contribution to the overall stability is fairly minimal - the amount may be even less than 5mm

3 weights on the bottom is going to put the camera too far away from the gimbal. This will make your shots less stable. You want the distance between the stage and the gimbal around 2-3 inches max. You'll need to add weights to the top to do this.

 

To understand this better, grab a pencil. Hold the pencil between the thumb and finger of one hand, and move the pencil with the other hand. Hold it in the middle. When you move the pencil, the eraser moves a lot. Now hold the pencil much closer to the eraser. When you move the pencil with your other hand, the eraser moves much less.

 

So in order to decrease the effect of sled movement on the lens, you want to get the gimbal closer to the lens. In order to keep a reasonable drop time (2-3 seconds), you will need more weight at the stage (top) in order to move the gimbal closer to the stage.

 

Honestly as a newb I am not sure I could even spin a perfectly set up rig flat !

It's not that hard to get DB with the Pilot. Just put the battery all the way back, the monitor all the way forward, and then just move the whole lower crossbar to redistribute bottom weight, and then compensate with the rear thumbscrew on the top.

[Sam Morgan Moore]

I think considering that the Pilot with three or so wieghts attached to the bottom (wich are in DB alone) the battery/monitors contribution to the overall stability is fairly minimal - the amount may be even less than 5mm

3 weights on the bottom is going to put the camera too far away from the gimbal. This will make your shots less stable. You want the distance between the stage and the gimbal around 2-3 inches max. You'll need to add weights to the top to do this.

 

My EX1 (and shotgin mic+fluff) only sits around 3.5 inches with 6 weights at the bottom - the post is short

 

My reasoning for this config is

 

short post = monitor close to me and easy to view and less risk of brushing rig with my legs !

 

Using the extra weights far from the post means more rotational inertia - easy to fly straight

 

Each set up it is a different set of compromises of course

 

One thing I am convinced is that the rig alway performs best when used near the maximum weight for the arm, however configured

 

S

[Dave Gish]

My EX1 (and shotgun mic+fluff) only sits around 3.5 inches with 6 weights at the bottom - the post is short

 

Using the extra weights far from the post means more rotational inertia - easy to fly straight

Yes, moving weights from the top stage to the ends of the lower crossbar will increase inertia in the pan axis, but it does not increase inertia in the tilt and roll axis. This means you need a lot more force on your left hand to control panning, but a much lighter force to control tilt and roll, which is difficult to say the least. The result is often bobbing (unintentional movement in the tilt axis) and/or wobbly horizons (unintentional movement in the roll axis). In addition, moving weight to the bottom moves the lens further away from from the gimbal, which amplifies unintentional movement in the tilt and roll axis. 3.5" from the gimbal to the bottom of the stage is not the best. The pros I've seen keep the gimbal much closer than this, except for when they need to get really high or low shots.

 

Lengthening the post will increase inertia in the tilt and roll axis, but it will also move the lens further away from from the gimbal, which amplifies movement in the tilt and roll axis, so this is generally a wash. I would only consider lengthening the post if you already have the gimbal within an inch or two from the bottom of the stage.

 

Adding more weight in general will increase inertia all around, but for tilt and roll axis, it doesn't really matter if that weight is on the top or bottom, since you end up moving the gimbal to maintain drop time.

 

Try moving a one of those weights from each end of the bottom to the top stage and see what happens...

 

Hope this helps.

Edited April 20, 2009 by Dave Gish

[Sam Morgan Moore]

Yes, moving weights from the top stage to the ends of the lower crossbar will increase inertia in the pan axis, but it does not increase inertia in the tilt and roll axis. This means you need a lot more force on your left hand to control panning, but a much lighter force to control tilt and roll, which is difficult to say the least. The result is often bobbing (unintentional movement in the tilt axis) and/or wobbly horizons (unintentional movement in the roll axis). In addition, moving weight to the bottom moves the lens further away from from the gimbal, which amplifies unintentional movement in the tilt and roll axis. 3.5" from the gimbal to the bottom of the stage is not the best. The pros I've seen keep the gimbal much closer than this, except for when they need to get really high or low shots.

 

Lengthening the post will increase inertia in the tilt and roll axis, but it will also move the lens further away from from the gimbal, which amplifies movement in the tilt and roll axis, so this is generally a wash. I would only consider lengthening the post if you already have the gimbal within an inch or two from the bottom of the stage.

 

Adding more weight in general will increase inertia all around, but for tilt and roll axis, it doesn't really matter if that weight is on the top or bottom, since you end up moving the gimbal to maintain drop time.

 

Try moving a one of those weights from each end of the bottom to the top stage and see what happens...

 

Hope this helps.

 

It was my guess that being further from the gimbal (and requiring therefore more force to displace through an angle) adding weights at the bottom improves (adds) inertia in all axis (axees?) gaining more inertia 'for the added wieght' - like lifting a see-saw is harder if the fat guy is sitting near the end !

 

You are correct that the lens of course deviates more with a higher camera due to the 'pencil effect'

 

Also weights at the bottom are further from the post centreline so give more resistance to pan too

 

I find that a resistance to panning helps isolate the rig from my body - and keep the camera flying straight which is generally my intention

 

I am aware however that there seems to be a difficulty in controlling rigs where the pan force and tilt/roll force are disparate - which maybe your point

 

The photos of GBrown (B+H) video and CPapaert (DVi review) show the camera 3 inches or more above the gimbal

 

CPapert has no weights at the bottom though (in the pics) - showing that probably either of those guys could fly the rig in almost any configuration although we dont see any GB footage - some of his 'shots' are bizzare in the extreme

 

I will try it

 

S

[Dave Gish]

It was my guess that being further from the gimbal (and requiring therefore more force to displace through an angle) adding weights at the bottom improves (adds) inertia in all axis (axees?) gaining more inertia 'for the added wieght' - like lifting a see-saw is harder if the fat guy is sitting near the end !

To be clear, adding more weight helps with everything (except your legs), so what we are talking about here is how a given amount of weight is distributed. In your analogy, it would be like comparing a fat guy on one end vs. a regular guy on one end plus a kid on the other end, and in both cases changing the hinge point of the see-saw until it balances. With a given length see-saw board, and a given amount of total weight at the ends, I believe the inertia at the CG would be the same no matter how you distributed the weight at the ends of the see-saw. That's how I understand it anyway.

 

I will try it

Let me know what you think!

[Afton Grant]

With a given length see-saw board, and a given amount of total weight at the ends, I believe the inertia at the CG would be the same no matter how you distributed the weight at the ends of the see-saw.

 

Not true. Rotational inertia, or moment of inertia of an object will always increase as mass is distributed away from the point of rotation, or axis.

 

Applied to Steadicam, weights moved away from the gimbal will NOT affect pan, UNLESS they're moved away from the post (axis for pan). Tilt and roll, however, have axes perpendicular to the post, so any mass moved away from the gimbal will increase inertia in tilt and roll.

[Dave Gish]

Hi Afton,

 

What is your typical distance between the gimbal and the bottom of the stage?

 

What we're trying to figure out here is if it's better to add screw-on weights low and increase the distance from the stage to the gimbal, or add these weights high and lose some inertia.

 

Applied to Steadicam, weights moved away from the gimbal will NOT affect pan, UNLESS they're moved away from the post (axis for pan).

Not sure how familiar you are with the Pilot, but the screw-on weights at the bottom are out away from the post, which definately increases pan inertia. Here's a picture:

Edited April 20, 2009 by Dave Gish

[Sam Morgan Moore]

My theory is that the weights at the bottom far from the gimbal aid pan and tilt more - because they are away vertically from the gimbal, they also increase rotational inertia more because they are more distant from the post - so provide best 'inertial value per unit mass'

 

My rig is virtually the same as your pic BTW, just 6 at the bottom rather than four and none at the top, my camera/mic must be heavier because it sits about the same height from the gimbal if not less as yours

 

S