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Old March 4th, 2003, 06:59 AM   #16
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Hi John,

I'm sure I've got some web space with my service provider, but if not then I'll sort out a couple of small files and send them to you. I'll also send you a picture of the washer modification.

Thanks.

John.
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Old March 4th, 2003, 01:06 PM   #17
 
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Charles wrote: "The shots that I am most proud of are the ones that so completely mimic a slow-moving dolly that no-one can tell the difference."

I think you hit the nail on the head! The same can be said about all camera work, in my humble opinion. If it calls attention to itself, then is wasn't successful.
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Old March 4th, 2003, 03:00 PM   #18
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Regarding this unbalanced gimbal issue: Casey, if you are checking in, please consider bringing this thread to the next staff meeting at Glidecam.

Considering that the V8 is a mature product and has been out for a while, it is disheartening to hear that there are manufacturing tolerance issues with this gimbal (which likely means other units are going out there with the same problem and the users are not as sharp as John S. to identify it). Placing a dummy weight on the sled, dropping the handle onto a pin mounted on the bench and giving it a spin is a quick procedure and perhaps should be part of the QC process if this issue is coming up on a regular basis.
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Old March 4th, 2003, 03:04 PM   #19
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Wow, I had no idea DVinfo was home to guys who've done hollywood movies! *giggles like a schoolgirl* Maybe we can work together one day.
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Old March 4th, 2003, 06:22 PM   #20
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Charles,

I believe Casey is now studying film in Boston...no longer at GlideCam...but I guess he's still got his contacts there and can pass on info from John. Casey...if you have a chance, why don't you chime in and tell us what you're up to now...maybe in the "These are the people in your neighborhood" forum would be better. Gotta keep up with family.
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Old March 5th, 2003, 06:02 PM   #21
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John, John, and Charles....I am in fact now studying film and sound in Boston. But it's only 45 mins from my hometown of Plymouth and Glidecam's offices. I never left Glidecam officially, im just on hiatus while persuing my studies...I'm still in touch with them and will likely be back with them for a while over the summer, as well as stopping by for a visit in a week or two. So i'll check in to the gimbal issue and pass along the key parts of this thread.

PS: Locke: i'll let them know if they get a call looking for a skoshi-washero, that you just want a small washer. ;)
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Old March 5th, 2003, 07:21 PM   #22
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Hi Casey, nice to hear from you and thanks for passing on the details of this thread. David Stevens at Glidecam has been really nice and very helpful so I certainly have no complaints, but Charles makes a good point with regards to the V8 being a mature product so really should balance OK out of the box.

I just wanted to get some more advice from you guys, I've been playing and practising and been messing around with the balance of the V8. So with the added washer I balance, then rotate 180 degrees and it's still OK, if I spin the post round that 180 degrees quickly as it's going round the sled rolls a bit, is this a dynamic balance issue? If I move it really slowly it appears to keep balance all the way around, with maybe a very slight roll but not as bad as when I spin the post quickly. I don't really understand dynamic balance too well, I tried to follow the threads on the steadicam forum but woooosh straight over my head :) A nice easy expanation of dynamic balance would be cool :)

Thanks guys.

John.
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Old March 5th, 2003, 08:22 PM   #23
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i would think Charles would be able to provide the best definition of Dynamic Balance!
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Old March 5th, 2003, 10:14 PM   #24
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Gee thanks Casey!

Nah, John, don't be discouraged that you heard that "woosh" sound. Dynamic balance is a hot button amongst the Steadi community, there are a bunch of different and painfully elaborate theories about what it is and how it works and what it ultimately means in practice. Suffice to say that my approach works for me but not for everyone.

When you have trimmed out the rig in the three axes (fore and aft, side to side and top to bottom) as you described, you have placed the rig into STATIC BALANCE. This means that the camera platform hangs level, the center post is vertical, and that you have properly adjusted the camera into balance with the rig.

However, the rig itself may not have been in a neutral state of balance to begin with. Imagine, if you will, a line that travels vertically up through the center post. This represents the fore and aft balance of the system. If the bottom section of the rig (where the batteries or counterweights live) is back-heavy, this straight line will now become diagonal, intersecting the sled at its true center of gravity fore and aft. (still with me? This is ugly without diagrams...!)

That line will now be exiting the camera platform somewhat forward of the center post (right? because it exited the bottom of the sled BEHIND the center post). This will ultimately be the center point of the camera when mounted, where you will find static balance. The problem is that when you spin or pan the rig, that diagonal line will attempt to turn itself back into a vertical line as the two masses (camera and sled) gravitate to their true balance. This is why you are finding the tendency for the rig to tip forward while spin balancing (a phenomenon known as "precession").

The remedy is to adjust the balance of the sled, then rebalance the camera. If while spinning, you find a tendency for the rig to tip forward (lens pointing down), this means that the sled itself is front heavy. Use whatever means necessary to adjust the sled, by changing the angle of the batteries or sliding the components (try to do anything that doesn't require ADDING weight!) to back-weight the sled, then rebalance the system by sliding the camera forward. Then try spinning again. It will take a while to get the hang of how much to adjust these things. The other thing that takes practice is getting a clean spin, especially at high speeds; in other words your hand shouldn't be influencing an odd rotation into the system. It's actually more beneficial to use a slow-moving spin to judge your dynamic balance, although it will be affected by the deficiencies in the design of the gimbal.

OK, there's a quickie lecture in dynamic balance! I'd be happy to clarify as necessary, obviously this is heavy stuff. Once you've found the sweet spot, you'll see a definite difference when making pans, especially whip pans. Good luck!
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Old March 5th, 2003, 10:50 PM   #25
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Sorry for volunteering you, Charles, but you're much better at explaining things technically than I am! That was actually an excellent definition. And the trouble with the V-8 is that it wasn't designed to let you "slide" things around that easy! This is where retooling your sled to add more options for adjustment is often a great idea! It might be a good idea to punch slots running down the center of the sled base (from front toward the back), one to the fore of the post and one behind it and mount monitor and batteries on these, allowing you to move each seperately to get the right balance. Ideally would be the same as the slots you'll see on the head assembly for adjusting the camera positioning.
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Old March 6th, 2003, 04:19 AM   #26
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Hey Charles, so far thats the best explanation I've read on dynamic balance :-) I'll have a play around tonight and see how I go. Also thanks to Casey for the advice but adding the washer to the V8 was cause for alarm enough without doing any major modifications :-) I'll try messing around more with the balance and see how it goes.

The way it is at the moment actually is a 5" LCD at the front with about 3 weight disks located near the monitor still on the front of the base plate then on the back of the baseplate there are about 10 weight disks, so there's a good chance that the weight isn't equally distributed across the base plate(I think I explained that right) so does this sound like it could be the problem?

Thanks.

John.
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Old March 6th, 2003, 04:22 AM   #27
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Geez, John...this is sounding like it's going to be trickier than I thought. I'm getting worried...
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Old March 6th, 2003, 04:46 AM   #28
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Don't worry about it John, we'll all be here to help when you get it :-) and besides, it's all part of the fun learning this stuff :-)

I've got my web space sorted, so I'll get some footage organised and posted, and if it helps John, I'll do a quick 5 minute training video for you to help you get started, the manual doesn't have any pictures so I'm sure it'll help.

John.
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Old March 6th, 2003, 05:00 AM   #29
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THAT would be greatly appreciated. Thanks, John!
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Old March 6th, 2003, 10:17 AM   #30
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John S: the weight may be in fact not distributed properly, so without further modification to the sled, it'll just take trial and error when placing the disks...which will take longer obviously than simply sliding the components forward and backward, but in the end will achieve the result.

Also, if you're doing whip pans or even continually spinning the sled for dynamic balance you want to be really careful of any monitor cables! if you have cable running from head to base of the sled on the OUTSIDE of the center post then you may run into hang ups on the gimbal. To prevent this, another simple and safe mod that will not void any warranties is one we even do on our demo V-8's down at the shop. Drill a hole in the back of the center post about an inch or so underneath the head...and another directly out the bottom of the sled base, right in the center of the post where it connects to the base plate. File the holes a little bit so they are nice and smooth and run an RG59 video cable in there (without any connectors)...leave some slack to allow for height adjustments in the post and terminate the cable in whatever connectors you may need for your camera and monitor (bnc on the monitor side, rca on the camera side is popular).

Once you've "internally wired" this way, you'll never have problems hooking a stray cable on the gimbal.

And yes, the manual for the V-8 could certainly be improved...i think that's another thing i'll bring up when i take a visit down there!
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