A buoyancy device

  • #1

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I want to make a device that can suspend in water via manipulating its density to as close to 1 as possible. I just thought that it will be cool to have a device that can stay in whatever position that I place it in the water.

Any idea of how this could actually be done? I was thinking about an airbag that can be squeezed or released precisely( just like airships), but how can that be done? Or are there other approaches?
 
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  • #2
phinds
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I want to make a device that can suspend in water via manipulating its density to as close to 1 as possible.
Such a device exists. It's called a scuba diver :smile:
 
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  • #3
Such a device exists. It's called a scuba diver :smile:
Yes, I am aware of that. I mean gadget sized devices:smile:
 
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  • #4
phinds
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Yes, I am aware of that. I mean gadget sized devices:smile:
It was actually intended as a hint to check out how they do it and see how that might be adapted to what you want
 
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  • #6
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I was thinking about an airbag that can be squeezed or released precisely( just like airships), but how can that be done?
Difficult: to keep the size of the airbag at different depths you need to increase its pressure. At ~ 12m depth, you need similar volume of gas as that bag originally had. Not impossible, but difficult, especially at 'gadget size'.

What I would try is some cylinder&piston like device with the mechanics inside.
 
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  • #7
Difficult: to keep the size of the airbag at different depths you need to increase its pressure. At ~ 12m depth, you need similar volume of gas as that bag originally had. Not impossible, but difficult, especially at 'gadget size'.

What I would try is some cylinder&piston like device with the mechanics inside.
Got it.
 
  • #8
OK. after a few days of thinking , this is what I came up with:
the weight at the bottom of the device will set it's density to roughly 1 beforehand.
The mechanism at the left end of the cylider will be connected to the piston on the right with a bar of some kind. The mechanism, which contains all the elecronics/sensors will detect it's movement in the water with some sort of acceleration detectors. Then it will precisely pull/push the bar which will move the piston
to change it's volume.

Will this work? (please ignore the part of how should I charge the mechanism, this is just a rough draft)

ps: The connection between the piston and the cylinder is water/air tight
 

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  • #9
B9501B0D-F744-45CF-90B4-0E3294B443BB.jpeg
Can digital accelerometers like adxl335 work on applications like this( I have an arduino nano), or is it not sensitive enough?
 

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  • #11
phinds
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Then it will precisely pull/push the bar which will move the piston
to change it's volume.

Will this work?
Looks to me like it should work just fine providing you can come up with an appropriate sensor/control mechanism to tell it when to move up and down. I have no idea if the accelerator you chose would work.
 
  • #12
Tom.G
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You will find it much more practical to use a pressure sensor for depth measurement.

To track depth with an accelerometer you will have to integrate all the changes of some very small signals over time. This is guaranteed to accumulate large and increasing errors over the time of a run. Realize also that your proposed diver will change orientation (tilt) depending on the relative position of the piston. So you will have to take account of all three accelerometer axis for each depth estimate. That calculation will likely introduce additional small errors, which will accumulate.

And how about using linear stepper motors to move the piston? What about that?
Sure; if you can figure out where there is room for the threaded rod with the piston retracted.
 
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  • #13
You will find it much more practical to use a pressure sensor for depth measurement.

To track depth with an accelerometer you will have to integrate all the changes of some very small signals over time. This is guaranteed to accumulate large and increasing errors over the time of a run. Realize also that your proposed diver will change orientation (tilt) depending on the relative position of the piston. So you will have to take account of all three accelerometer axis for each depth estimate. That calculation will likely introduce additional small errors, which will accumulate.


Sure; if you can figure out where there is room for the threaded rod with the piston retracted.
Thanks for the advice, but, I have a small question:
This project is actually more of a demonstrative device which I can show to my friends and teachers, which means it will not be operated in a pool or anywhere with the water depth greater than 2m, but rather a big tall clear bucket about 1m tall. So will the water pressure difference be significant enough for the sensor to pick up? If so, will this one work? Or do you prefer other models?

https://www.dfrobot.com/wiki/index.php/Gravity:_Water_Pressure_Sensor_SKU:_SEN0257
 
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  • #14
Tom.G
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Alright, time for you to do some research. You need to find:
  • The pressure under 2m of water
  • A pressure sensor:
    • Where that water pressure is a signifcant fraction of the sensor pressure range
    • That will operate with whatever supply voltage you have available
    • That has an output signal that you can interface with whatever control electronics you are using
    • Of a physical size to fit in your gadget
    • Is easy to mount
    • With a cost that is within your budget
    • Is available for delivery soon enough that you can meet your project deadline

Oh, and for the overall project, pay attention to Murphy's law: "Anything that can go wrong, will." :eek:

(and... Welcome to the wonderful(?) world of Engineering.)

Cheers,
Tom
 
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  • #15
Thanks!
Is available for delivery soon enough that you can meet your project deadline
I don’t actually have an deadline, which is great news.
Oh, and for the overall project, pay attention to Murphy's law: "Anything that can go wrong, will." :eek:
Oops!
 
  • #16
Tom.G
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Oops!
Not a big deal, it's called 'getting experience!' (eventually you build a huge personal library of what NOT to do)
 
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  • #17
Not a big deal, it's called 'getting experience!' (eventually you build a huge personal library of what NOT to do)
Ha. Got it.
 
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  • #18
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And how about using linear stepper motors to move the piston?
Ebay is littered with those small linear steppers (guess they are from some massacred ticket printers or similar). Good choice.

Ps.: just one thing. You will have a battery, electronics, and a motor. Why not use them as ballast? Put all those at the bottom of the standing tube, and then it'll not tilt. You can add external weight later on to the bottom outside if it is not enough.
 
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  • #19
Ps.: just one thing. You will have a battery, electronics, and a motor. Why not use them as ballast? Put all those at the bottom of the standing tube, and then it'll not tilt. You can add external weight later on to the bottom outside if it is not enough.
Actually, perhaps just letting it be like this will be fine.
3E0D573C-1EB3-4BF3-82C6-73647F8A8928.jpeg
 

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  • #20
tech99
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I want to make a device that can suspend in water via manipulating its density to as close to 1 as possible. I just thought that it will be cool to have a device that can stay in whatever position that I place it in the water.

Any idea of how this could actually be done? I was thinking about an airbag that can be squeezed or released precisely( just like airships), but how can that be done? Or are there other approaches?
How about the "Cartesian Diver" as a basis. It consists of a sealed plastic drink bottle containing water, and the diver is a test tube containing part air, so it just floats.It can be made to ascend or sink by adjusting the pressure of the water by squeezing the bottle.
 
  • #21
How about the "Cartesian Diver" as a basis. It consists of a sealed plastic drink bottle containing water, and the diver is a test tube containing part air, so it just floats.It can be made to ascend or sink by adjusting the pressure of the water by squeezing the bottle.
Well,about having Cartesian divers as my concept, this is the reason that I am not using it:

Cartesian divers float/sink by squeezing the bottle outside, which means the diver itself is passively changing its density. But since in my case, I can’t manipulate the density around it, I need the device to actively change its density.
 
  • #22
  • The pressure under 2m of water
  • A pressure sensor:
    • Where that water pressure is a signifcant fraction of the sensor pressure range
    • That will operate with whatever supply voltage you have available
    • That has an output signal that you can interface with whatever control electronics you are using
    • Of a physical size to fit in your gadget
    • Is easy to mount
    • With a cost that is within your budget
    • Is available for delivery soon enough that you can meet your project deadline
I just found something:ms5540c
A video using the exact pressure sensor to measure well,water pressure.
Perhaps this will work on my project:smile:
 
  • #23
Tom.G
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Following the link in the video was a dead end. That part number was not listed on their site. If it meets the stated requirements (and any others you can think of), try it and see. (It's called Research and Developement, or R&D, if you have done the research then it is time for the developement. :smile:)
 
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  • #24
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That is cool. If you succeed, don't forget to share the tutorials.
Maybe you should try:
1. actuator: piston. <-- Manipulate the density of whole device.
2. sensor:
------pressure sensor. <-- Sensing the current depth.
------thermometer. <-- Sensing the temprature and calculate the density of water.
3. controller: SoC or other type of controller. <-- Manipulate the density of system according to density of water.
4. other part: metal added to increase the density.
Good luck!
 
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  • #25
------thermometer. <-- Sensing the temprature and calculate the density of water.
I hadn't think about that yet. Good advice!
 

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