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Seaglider with ballast tank


Nice to meet this forum.

Hope that “general discussion” is the right place to write about this topic since so far is just an idea :slight_smile:

I am on a project regarding the building of a seaglider. I am thinking in purchasing most of the parts from Blue Robotics but I have some doubts if they can actually be used for this.

First and just to clarify it, the seaglider I want to build is as those used for marine research: hydrodynamic hull, two kinds of wings to glide up and down and a ballast tank in their inside.

To simplify the concept I’ve thought in add a pressure sensor (the bar 30 in instace) and program the full system that to a certain depth the glider release the water from the hull and when getting another certain depth at shallow waters, drag the water outside the hull.

The ballast tank I’ve thought to, would be as follows: a T-200 motor (with cable and penetrator included) with some 3d printed centrifugal blades and cage attached to it for using it as a water pump. The water would get into a balloon that, at the same time, would be inside the hull.

So here arrive my doubts:

  • Since all the electronics and power system would be in the same place that the balloon: wouldn’t the stmospheric pressure created when the baloon inflates, damage the electronics or battery?

  • How could I seal the tube for transporting the water inside the baloon around one of the hole’s cap?

  • Can actually be the T-200 motor be used as a water pump with the blade’s modification I’m planning to do?

Thanks in advance.

Welcome to the the community Tega,

You can use the electronics in the acrylic housing up to 100m, with some programming the 30 Bar sensor would be able to tell the glider to take on water/release by switching an onboard pump.

As for the T200 be used for the water pump, this is a tricky one! I doubt very much that it could act as a pump as its not really designed for this role.

90 % of the other electronic will certainly do the job you want it to do.

Will the glider be tethered?
What depths would you like to go?
Duration of mission?
Online recording or data recovery?

Happy to help you through this little problem you have.

Kind regards

Deep Supplies

Hello again and thank you very much for the welcome and answer :slight_smile:

Regarding what you asked me:

  • No, the glider will not be tethered so far I’ve thought
  • Probably from 30 to 40 meters depth
  • Few days working, testing basic technology
  • Data recovery

Regarding that 90% that would works. Which would be the other 10% that may won’t work? I’m pretty worry that I mess it up a bit with the battery, seems such a senstive device.

The electronics will be inside the acrilic so if they stands until 100m… No problem. But still, the balloon would be sharing the same space that the electronics, that’s why I’m afraid that the battery (in instance) get damaged when the balloon inflates of water, increasing the air pressure inside the hull.

Again thanks for the help.

I would investigate fitting a small pump into a pressure vessel and connecting the fluid lines through the enclosure cap with NPT or NPTF tube fittings. You might want to try using soft tubing that gets pressed onto “hose barbs”. You would have to see if that type of connection will be suitable for your pressure. Re-engineering the T-200 into a pump would take some considerable knowledge of prop/pump design, which might not be worth your time.

I wouldn’t worry about the other things getting crushed from the atmospheric pressure. However, you will need a limit switch for the balloon to press against once it is full. The switch will prevent the balloon from overinflating. You could always house your electronics inside another small enclosure inside that enclosure as well.

You should easily be able to fit a suitable pump into one of the BlueRobotics enclosures. At 40 meters, you’re only going to be working with about 60 psi of pressure, so it shouldn’t be too difficult to source a 12 or 24 VDC pump. In the setup that you described, if you use anything other than a peristaltic pump, you will also need to run some electronic valve between the flexible ballast and the pump so that water doesn’t get immediately pushed back out once you shut off the pump. You should try to have the pump below surface level so it doesn’t suck in air, which will decrease efficiency.

It would be best if you considered implementing small zinc screens into the fluid path before the inlet to serve as a sacrificial anode to help mitigate corrosion if it’s going to be in seawater. Furthermore, you will need a filter to prevent aggregate from getting sucked into your ballast and damaging it.

You could consider using a hard-plastic ballast tank (like a plastic bottle) housed inside a larger pressure vessel. If you do this, then you will need a higher-pressure pump. Air will get compressed inside the ballast as it fills and has nowhere to escape and little space to compress, which means you can only flood the tank to about 3/4 full. You can circumvent this if you implement a vent valve at the top, but that’s another valve (another failure point + incurred cost). I think your setup is the best value for your operating depth.

So, to reiterate, try to find a peristaltic pump that will fit inside an enclosure, and make sure to implement a shut-off switch, so the pump knows when to stop. Best of luck!

Tyler Sims,

Thank you so much for your answer. I like the idea about the think anode!!

Yes, I also think, now that I’ve been gone through possible designs for the water pump, don’t use the T-200. As you say, it would take too much time.

Just to clarify, with hard-plastic ballast tank, it would require to add a kind of piston to the system, right?

Again, thank you for your answer.

Glad to help TeGa,

The hard ballast tank described above would not require a piston. I was saying that with a hard ballast tank, people sometimes include a vent tube at the top to allow air to escape while flooding it so the ballast will fill completely. Optimally there would be a valve on this tube. If you don’t use a vent tube, that’s fine; it just means you that the ballast won’t be able to fill completely since there’s going to be a compressed air pocked stuck in there, which also means you need a bit stronger pump to force water in.

RC-Submarine.com has lots of useful free information about systems used for small ballast systems. I’ve gone ahead and photocopied the pages, which I think you will find most useful, but you can also visit this page (https://www.rc-submarine.com/rc-submarine-technology) to see a full list of ballast systems. Just note that their current diagram for a compressed air ballast is missing a vent at the bottom of the tank, they recently redid the diagrams, and they must have missed it by mistake.

Here is the info that will help you visualize the systems I described before (https://imgur.com/a/SfW6xxs). The first one is a vented hard ballast, the second is a non-vented hard ballast, and the third is the flexible ballast like you initially talked about.

Please let me know if I can clear anything up!

Hi TeGa,

I was reading about the Seaglide Project earlier and thought that their ballast system may be of interest to you. It is a piston style ballast.

Here’s the project as a whole: http://seaglide.org/build-instructions
Here are detailed instructions on their ballast: https://static1.squarespace.com/static/52f69916e4b0393d858e6f9f/t/5b76d9270e2e723dde1cacfd/1534515520526/2BE.pdf

Tyler Sims

Hello again Tyler,

Awesome!! Thank you so much for you help. Definetly very usefull information. I will go deeply through all the components and try to choose the best that fits for me.

Regarding the vent tube, yes, I guess I won’t need it. Now I understood :slight_smile: I think will fitt perfect whichever of the other suggestions you have sent to me.

Again, thank you very much. Impressed for the help received :slight_smile: !!

1 Like

TeGa -

How is your project coming along? Have you put any hardware together yet? I am interested in building a glider, too.

Hello Bill,

Working still in some designs ( just some rough draws :slight_smile: ). I am doing a deep research in the parts I’ll purchase to keep the price as low as possible. Guess I will get to put all together but still without knowing if I will be able to carry out fully this idea.

Is going your glider going for greater depths than 40m? So far, I am just planning to keep it there to just test the basis of my design.

We’re planning on going to 400m in the open ocean.



Cool! Yes, think you are going bit more professional than my project haha. I am in a much earlier phase.

Best of luck.