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Old October 24th, 2005, 09:58 PM   #16
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Hah, now I'm getting a pile of spare aluminum too. I've got 16 great 82mm inline wheels, with about 40 feet on them, and new ABEC3's to boot in case anyone's looking. My wife will be so thrilled with the new wheels.

I don't need luck..I need the fortitude to keep flashing my visa all over town so every sports vendor will acknowledge my insanity.

I tried moving the wheel pod's axles closer as well as increasing the gap between the wheels to no avail. I've concluded that inlines will only work with a more "prepared" track which is not my goal. The 90 degree skater wheels will hopefully be better as will be the improved pod rotation setup. The lazy susan bearings are just not solid enough...as I was surmising originally. Tighter bearings with fancy spring suspension sounds nice though. If nothing else Dan, my little tale here is a testament to all the time you've no doubt put into your dvrig designs.
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Old October 24th, 2005, 11:11 PM   #17
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Several things to consider:

Inline skate wheels may be too narrow. Use skateboard wheels which are usually a couple of inches thick and will ride a little more easily and make less noise. Talc works well. I have used that on my curved steel Matthews track and it works like a charm, but, otherwise I never need it on the straights.

The trucks for the wheel need to pivot and slide as the dolly moves through the curve. Having a slot will help ensure a smooth curve. Also using an ultra hard plastic washer, or block helps make the trucks move with ease. the plastic is hard enough that even when a large tripod, jib, weights and sandbags are on it, it is still smooth.

Consider the width of the dolly. Most doors are about 28 to 35 inches wide, not sure what the industry standard is. My dolly deck is about 26 inches wide, but I have sideboards that I can bolt on to make the dolly18 inches wider for the great outdoors or larger rooms. With the narrow dolly I can still fit through doors. Industry standard track is usually 24.5 inches wide, center to center. There are a couple of other widths, but 24.5 seems to be the norm.

Having curved track in tiny NYC apartments is a help, because it seems like almost all jibs are too big and get in the way of the shot.

I am in the process of rebuilding the dolly, so that it can negotiate the corners easily. I had the wheelbase too long and only two of the four trucks could slide. I had a machine shop cut the other two trucks so the the pivot hole became a long slot. The trucks are chromed "V" track with a flat piece welded on top and two wheels on each side of the "V". The chrome trucks effortlessly turn as the dolly moves.
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Old October 25th, 2005, 09:10 AM   #18
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Thanks Mark. The new wheels are indeed 101a durometer skate board wheels. I agree that inline wheels are inappropriate mounted at 90 degrees do the rather large slip angle on a rounded wheel surface. Fortunately the bearings are the same though. I have some two inch aluminum L bracket with flat stock to weld to the top...just like yours.

Rather than using a slot, I'm articulating two of the arms. This means the dolly has a potential track width from about 24 to 34 inches as the arms rotate from fully inboard to fully outboard. I've found that two flanged bearings (like wheelbarrows use) and a bolt make a very low deflection rotating joint however I also have a selection of impregnated bushings on order to see if they will work OK. The nice thing about using bearings is that properly bushed, they can be torqued down a great deal for a very low deflection, but freely rotating joint.

With four rotating wheel pods, two of them on articulating arms, it's an absolute cluster off the PVC track. I'm therefore setting the pods up to be lockable for use off track. The goal of course is having one unit that:

1. Has next to zero setup time.
2. Has very low track prep time.
3. Is very smooth and stable enough for my jib.

The site that was hosting the pics had a double whammy of hack and database move...so my original pictures are gone. I'll update this thread with my next iteration.
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Old October 25th, 2005, 12:34 PM   #19
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Yeah, I couldn't see the pix. Curious to see it. Almost sounds like a spyder dolly.

My dolly is pretty much set up for track only, but it would be nice to have street wheels on it to use it as an equipment cart, or to dolly on smooth surfaces. But I would have to have some kind of steering system. Maybe on Version 2.
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Old October 25th, 2005, 01:24 PM   #20
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The spyder was my inspiration. I should have gone with their skate wheel setup right off the bat instead of doing the inlines.
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Old October 25th, 2005, 11:16 PM   #21
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Eh. It's an experiment. My dolly isn't exactly how I want it, It'll get a few more upgrades. I'm not too worried. Most people are just thrilled that I have a dolly, they're not too worried as long as it's smooth and quiet.
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Old October 30th, 2005, 10:12 PM   #22
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Ok, the redesign is now complete. This dolly now has rocking, rotating and articulating wheels. Basically you throw your PVC down, straight, curved, whatever, as long as it is 24 to 36 inches apart the dolly will track it. The skater wheel design works much better in this application than the inlines.


There are a few pics and a short video here. The video shows the dolly going over bump created by putting a piece of 3/4" wood under one rail. This would have derailed the non-rocking inline wheels in a second.
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Old October 31st, 2005, 08:40 AM   #23
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Great Job! Congrats!

Dan
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Old October 31st, 2005, 08:50 AM   #24
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Thanks Dan. I now, more than ever, appreciate the work you put into your designs. This project had about $140 in sunk costs, plus a good 10 hours in experimentation.
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Old October 31st, 2005, 09:13 AM   #25
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Well worth the effort! It turned out really nice. It reminds me of the Flex Track "floating" wheel design. You could probably get away with using something like their track. You should see what you can find in some sort of large diameter hose and try it out.

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Old October 31st, 2005, 12:40 PM   #26
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Dennis, nice work. It helps that you can do your own welding. I've thought about learning. I'm going to look around for a machine shop that can do the metal work.

The only things I can thing of are: you may want to add some braces to the tower for stability, or perhaps a beefier tower? The one square tube just seems a bit too twig-like for my safety paranoia. Maybe make the back end of the crane a bit longer so that you won't need so much weight on the rear. As long as the tower is high enough, you won't have to worry about the back end bottoming out during the shot.

Nice job.

Some tips Jim Taylor, a great DP, gave me if you are going to be throwing down PVC: bring a couple of brooms to sweep the track area and also a few sound blankets to go under the track. The blankets eliminate the popping of grit against the PVC as you dolly and smooths out slight imperfections in the terrain. Just be sure that the blankies are not used for anything else as they get pretty nasty, pretty quick.

If you can find deals on steel track, it's worth it, especially with a set up as heavy as yours.
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Old October 31st, 2005, 02:43 PM   #27
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Mark, thanks for the tips on track. I've seen neoprene recommended too...same idea.

Because everything is aluminum, the rig looks a lot heavier than it is (about 60 pounds). In fact, I had no problem carrying the complete rig (minus the weights) from the shop to the yard outside. I considered bracing the tower but it's very stable as is. It's 1/4" wall 2 inch aluminum tubing...and what you can't see is the second collar below the tie in plate. So basically the base drops down about 6 inches into a second collar. It's the two that make it stiff. I did this to allow use of a tripod with the mast removed.
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Old October 31st, 2005, 03:34 PM   #28
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Okay, sounds good. If you've got the jib up high on a windy day how much do you think it would sway? I'm not being difficult, just making sure you don't get sued.
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Old October 31st, 2005, 03:42 PM   #29
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Well, the windy test with the cam fully upright is yet to come...plan B is a triangulated setup using stainless rod and a few turnbuckles. That's a last resort as I'd like to keep the platform clear. The skater wheel assemblies are much stiffer (near zero play) which contributes to a lot less platform wobble over the previous setup using 3" lazy suzan bearings.

One thing I've learned here though is that predictions and basic engineering don't always predict field performance :-)

Edit: Mark, I did some checking tonight. There's a couple millimitres of sway at the tower head when I force a wobble. That in itself is not a big issue...but a few mm at the tower end means a lot more at the jib head. I'll be adding a triangulated support system.

Last edited by Dennis Wood; October 31st, 2005 at 08:46 PM.
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