Homebuilt ROVs Forum

I've been working on a new concept idea to make an ROV subrmege and surface by replacing it with changing the volume of the ROV. After a semester of working on the project. I've built a prototype. But my research tells me that this concept needs a very complex design, because when we change the volume of an object, the centroid change and therefore the centre of gravity is not below the centroid. The ROV will go out of balance.

As i know the industrial ROV uses the ballast tank technology to submerge. And i only saw thrusters for the mini ROVs for an external force to push the ROV up and down. Won't the buoyancy force force it up again? how do u sustain at certain depth?

I think that if you adjust the buoyancy for neutral just under the surface, as you dive you will lose buoyancy due to the pressure on your vessel, pressing it inward and reducing the volume of air? Any divers on the board interested in confirming this?

I think that this is a complex idea, it might depend on several things. First, if the bouyancy chamber is sealed and water is mecahnically pumped in , the bouyancy shouldnt be affected, as the water pressure couldn't compress the air in a closed chamber. Much like a scuba tank with a little water inside. secondly, if your design leaves the bouyancy chamber open to barometric pressure as the ROV descends, the increase in water pressure would compress the trapped air so much that it would change the bouyancy fairly quickly, potentially upending your ROV. I think a sealed bouyancy chamber would have the best results, but the need to have a dynamic water pump that could pump water in and out of the chamber for ballast to maintain desired depth would be the toughest part. However, if the ballast chamber remains at the top of ROV, I wouldnt think it would go out of balance. Best of luck. Cheers.

I think that this is a complex idea, it might depend on several things. First, if the bouyancy chamber is sealed and water is mecahnically pumped in , the bouyancy shouldnt be affected, as the water pressure couldn't compress the air in a closed chamber. Much like a scuba tank with a little water inside. secondly, if your design leaves the bouyancy chamber open to barometric pressure as the ROV descends, the increase in water pressure would compress the trapped air so much that it would change the bouyancy fairly quickly, potentially upending your ROV. I think a sealed bouyancy chamber would have the best results, but the need to have a dynamic water pump that could pump water in and out of the chamber for ballast to maintain desired depth would be the toughest part. However, if the ballast chamber remains at the top of ROV, I wouldnt think it would go out of balance. Best of luck. Cheers.

I'm going to presume that all parts of your sub are solid, (PVC, Metal, etc), and that non of it will change shape significantly under high pressure. Because of this, the sub's volume is constant at any depth. Water's compressibility at depth is very very small, so much so that it is considered an incompressible fluid. So in essence the density of water on the surface and 100m below the surface are both ~1.0g/mL. Thus if you achieve neutral buoyancy at the surface, you will essentially have neutral buoyancy 100m down.

This indeed would be quite a challenge.

I have used systems in the past that have what we call in the industry as soft buoyancy, e.g tanks that can be flooded or blown to alter the buoyancy of the ROV.

However these ROV.'s still need some form of regular buoyancy to prevent the ROV turning over.

However you buid an ROV its pretty much a given that it will be heavy towards the bottom of the ROV using ballast weights or design to keep the orientation correct, and as such you need buoyancy towards the top of the ROV to keep it upright also.

Getting back to the soft buoyancy a proven system is two tanks either side of the rov that are open to the sea by means of a standpipe inside the tank with a flooding solenoid valve and a compressed gas system with valves to blow the tanks.

The purpose of the standpipes is to allow the gas to expand and escape during ascent to prevent bursting the tanks.

In practise the system works very well as you trim the rov to be positive when the tanks are fully blown on surface and neutral when about have full of water.

This then allows you to trim the ROV so it perfectly neutral in the water at whatever depth within reason, which is great for flying around the bottom if there is a lot of sediment.