Lo-cost, Lo-tech constant* buoyancy arms

[yyip 0]

A while back on a Wetpixel thread I pondered the feasibility of using plastic soda (or pop as we say up here) bottles to offset the negative buoyancy of my rig: http://wetpixel.com/forums/index.php?act=S...st&p=107218

 

Disclaimer: Its not pretty for those of you who use cameras as chic magnets, and I make no claims on the safety aspect of this application.

 

I have since reduced the concept to practice, added a new twist, and tested it in the field. The new twist is adding schrader tire inflation valves to the bottle caps, and pre-pressurizing the bottle with the BC inflator hose and a tire filler adaptor.

 

Since the soda bottles have ridges on them, they do not lie flat against the strobe arms. To reduce play between the arm and bottle I applied a zip tie around the duct tape to cinch up slack. This turns out to be very effective, and the combination is rigid enough to adjust strobe position via the bottles. The quality of duct tape matters, some stretch more and rip easier than others (I was employed by 3M, and still own stock). I would occasionally re-cinch the zip ties to take up slack from stretch.

 

The tire valves are from an auto part store and cost about US$0.39 each. The bottle caps are right off the Pepsi bottle (I do not own stock). A 0.5" (12.7mm) hole drilled into the cap accommodates the self sealing valves just fine. Total cost per arm: US$1.39, including beverage of your choice.

 

Excessive buoyancy can be compensated by adding water to the bottles.

 

Results:

 

With my Aquatica D200 and pair of Inon Z220S strobes, I can achieve neutral buoyancy with wide angle setups (sometimes having to add water to the soda bottles). With the 105VR and Fisheye focus light, the rig can still be handled with fingertips.

 

I made 38 dives without having to replace the duct tape assembly. I could have easily made 38 more dives with the setup.

 

The lift created by the dome port can be offset by twisting strobe arms to position the bottles further back. Macro set up with the arms forward compensates for the negative port/lens. The separation of positive and negative centers of buoyancy creates a torque (twisting force) when the rig is not near horizontal. Vertical shots require some muscling. In the future, I want to try two smaller bottles placed closer to the Z220s, and a 20 oz (0.6l) directly under the housing.

 

Notes about safety:

Soda bottles must withstand at least 60 psi, since that is the pressure of a hot soda in the trunk of a car. There is whole "sport" of using plastic soda bottle to make water rockets, there is a lot of info online wrt to this safety, altho this is a boy scout type activity, so its very conservative. At first I was quite sheepish about how much pressure to apply, using a tire gauge, progressively went up to about 80 psi. Then I attached it to my bicycle pump, and maxed it out at 130 psi. Then I dumped what ever my 2nd stage is set at into it. I then filed it to 100 psi, taped on a broom handle and beat it against the garage floor, finally I whacked it with a a sledge hammer. No failures were encountered. It did fail when I stabbed it with a knife and shot it with a bb gun. The failures were benign, hissing, not exploding. Now I regularly fill them up to 80 psi which will keep them fully inflated to 150 fsw.

 

 

[MikeVeitch 0]

hehe.... def not pretty!

 

but if it works! go for it

[kriptap 0]

How negative can your rig be?

[yyip 0]

The two bottles provide ~1.2kg (2.5 lbs) of lift. So that is about the net weight uw with WA setup. I estimate the macro setup to be ~5 lbs.

 

However, what is more important especially when shooting single handed is the leverage created by the unsupported weight x distance of the lever arm. Which in my case with the an Inon strobe & 20" of arms & 12" of housing is significant and hurts after multi-days of diving. (ie: its more work to hold a stick from one end than balancing it in the middle) Placing the bottle in between the housing and the strobe acts like a balance. Which is why I am interested in trying a small bottle as close to the strobe as possible, which would effectively eliminate the weight at the end of the stick, without creating a dumbbell balance.

[Don in Colorado 2]

I like the concept. I like the price. Good thinking. Thanks for sharing.

[markdhanlon 0]

How did you connect your 2nd stage to the inflator valve? I would like to replicate this. Thanks.

[yyip 0]

Most dive shops sell a tire inflation valve which can be attached to the quick disconnect on your BC inflator hose.

 

http://www.leisurepro.com/Prod/CategoryID_...QUTI.html?Hit=1

[JackConnick 76]

Fun idea. But what happens when the inflators pop out? Does the whole rig go round in the water like one of those rocket wheels?

 

You really could have something here. Put big enough bottles and have a rocket powered camera!

 

Ok, ok. Good idea, I'd hate to have to swim it in a current.

 

Jack

[davidrodkeller 0]

A while back on a Wetpixel thread I pondered the feasibility of using plastic soda (or pop as we say up here) bottles to offset the negative buoyancy of my rig

I've never done anything like this, and and I don't want to disregard or disrespect anyone's desire to alter their rig's bouyancy, but I'd like to ask if the effort to push it thru the water isn't at least equal to the effort to handle it without counteracting the negative bouyancy. And given that in current and surge a streamlined negative rig is helpful, doesn't adding lift and surface area to the rig become something of an issue in and of itself?

[cor 0]

I've never done anything like this, and and I don't want to disregard or disrespect anyone's desire to alter their rig's bouyancy, but I'd like to ask if the effort to push it thru the water isn't at least equal to the effort to handle it without counteracting the negative bouyancy. And given that in current and surge a streamlined negative rig is helpful, doesn't adding lift and surface area to the rig become something of an issue in and of itself?

I dont know what other people's reasons are to try to make their rigs more bouyant, but for me making it easier to push isnt the main reason. My D2x housing is so negative, it actually hurts me after a while if I do longterm macro imaging. I dont care about the (imho slight) negative impact of it being more neutral, i do care a lot about my arms not feeling like dead weights after a few dives

 

Cor

[davidrodkeller 0]

I dont know what other people's reasons are to try to make their rigs more bouyant, but for me making it easier to push isnt the main reason. My D2x housing is so negative, it actually hurts me after a while if I do longterm macro imaging. I dont care about the (imho slight) negative impact of it being more neutral, i do care a lot about my arms not feeling like dead weights after a few dives

My point was that the added appendages make the rig more difficult to move thru the water (given the resistance increase due to the surface area increase)....kind of like a big dome does....so i wonder what is gained. It seems like a trade: effort to handle the rig vs. effort to move it through water.

[cor 0]

My point was that the added appendages make the rig more difficult to move thru the water (given the resistance increase due to the surface area increase)....kind of like a big dome does....so i wonder what is gained. It seems like a trade: effort to handle the rig vs. effort to move it through water.

I think the main issue is not how buoyant your rig is, but how bulky because of added buoyancy devices. I have been diving with a basically neutral Subal/D2x housing for 100+ dives, and I noticed a very slight additional drag. It's so slight, that it barely registers. But I think this is because the bulk of my housing did not really change by adding buoyancy. I wouldnt be surprised that it could be annoying if you added some very large buoyancy devices. For me the benefits of a neutral housing far outweigh the almost nonexistant negatives..

 

Cor

[ZebraMussel 0]

I think the main issue is not how buoyant your rig is, but how bulky because of added buoyancy devices. I have been diving with a basically neutral Subal/D2x housing for 100+ dives, and I noticed a very slight additional drag. It's so slight, that it barely registers. But I think this is because the bulk of my housing did not really change by adding buoyancy. I wouldnt be surprised that it could be annoying if you added some very large buoyancy devices. For me the benefits of a neutral housing far outweigh the almost nonexistant negatives..

 

Cor

I am Using a Sea and Sea dx 200 with Sea and Sea strobes and find it very uncomfortable because of the negative bouyancy. The first thought that I had was to attach some closed cell foam on the bottom of the housing. My thought would be to use velcro attached to the housing and to the foam so different thicknesses of foam could be used depending on which port was attached at the time. It seems to me that the big dome port is more bouyant than a smaller flat port. Has anybody tried this? What would the foam do to the handling of the housing?. It would seem to me that this would be more streamlined and would give more options. I understand it would take a lot of trial and error to get the bouyancy just right....but it may be worth it in the long run. Any opinions one way or another on if this will work or not?

[buddy 7]

I think the main issue is not how buoyant your rig is, but how bulky because of added buoyancy devices. I have been diving with a basically neutral Subal/D2x housing for 100+ dives, and I noticed a very slight additional drag. It's so slight, that it barely registers. But I think this is because the bulk of my housing did not really change by adding buoyancy. I wouldnt be surprised that it could be annoying if you added some very large buoyancy devices. For me the benefits of a neutral housing far outweigh the almost nonexistant negatives..

 

......

dont know what other people's reasons are to try to make their rigs more bouyant, but for me making it easier to push isnt the main reason. My D2x housing is so negative, it actually hurts me after a while if I do longterm macro imaging. I dont care about the (imho slight) negative impact of it being more neutral, i do care a lot about my arms not feeling like dead weights after a few dives smile.gif

 

Cor

 

what is it now your D2X housing: negativ or not??? my subal / D2X is rather neutral (very slightly negative) !

 

hehe.... def not pretty!

 

but if it works! go for it

 

 

slightly under exagerated. I would rather say fu...ing ugly!!!!

ha ha ha

[cor 0]

what is it now your D2X housing: negativ or not??? my subal / D2X is rather neutral (very slightly negative) !

My subal/d2x with normal ULCS arms and 2 x YS90DX and focus light was too negative for me. Thats what i meant with '..my d2x housing is so negative...', which should have been '..my d2x housing was so negative...'.

 

I recently added some buoyancy arms, which made it neutral (although these can be adjusted however you want them to be)..

 

Cor

[cor 0]

I just posted a review of the buoyancy arms im currently using in the Techniques & Tips forum (someone feel free to move it if thats the wrong place...)

 

Cor