The Random Thoughts of a Geek heading for Banbury

# ROV – Part 1: Project Overview

One of the things I fancy doing with my free time; and to help me learn to program/built awesome things is to geek out is to try and build an ROV (Remotely Operated underwater Vehicle); I am not sure why the “U” runs away and hides; it could be to do with the pressures that are involved.

Hobby ROVs

With an increased interest in the ocean by many people, both young and old, and the increased availability of once expensive and non-commercially available equipment, ROVs have become a popular hobby amongst many. This hobby involves the construction of small ROVs that generally are made out of PVC piping and often can dive to depths between 50 to 100 feet but some have managed to get to 300 feet. […] Most hobby ROVs are tested in lakes where the water is calm, however some have tested their own personal ROVs in the sea. – From Wikipedia

As with most water craft (boats etc) the part of a ROV that is underwater should be water tight; while boats have a large amount of them above the water that can be full of holes, ROVs and Submarines loose out on that grace, also boats can be almost water tight; and rely a number of methods of either sinking very slowly; kicking ingress water out faster than it comes in (pumps, sponges, etc) and or using prop tubes that are interspaced with grease that stops water at atmospheric pressure sneaking in, However ROVs operate under larger presure (RC Subs tend to not be designed to operate as deeply as miniature ROVs).

## Under Pressure

Pressure increase at depth, as the little diagram acquired from CalcTool shows the greater the depth, the greater the pressure; I used their assumption of the density of sea water to be 1025 kg/m³ (‘Fresh’ water is less dense), which means that pressure increases by approx. 1 atm with each 10 m of depth.

I ran the calc tool a small number of times and came up with the following graph; The Calculator gives the total pressure – not just the pressure due to the water, so it includes the 1 atm ambient air pressure at sea level.

This 1 atm ambient pressure should be the same 1 atm as inside the ROV at the surface, so the net force on the hull at the surface should be 0 atm.

As well as atm I ran the pressures as kgf/cm^2 and all the way to 60 meters below the surface;  I doubt very much if I will need to build that level of pressure resistance into my first attempt; but its worth illustrating.

Also at some point it may be worth re-running this in SI units (1 atm = 1.03 kgf/cm^2 =  101 kPa)

Most hobby ROV builders use PVC pipe from plumbing suppliers, despite it comming with the following warning:

PVC pipe tends to shatter into small splinters or shrapnel when it explodes and not all PVC is pressure rated.

NEVER pressurize PVC pipe with air, hydro-testing (water) is the only way it should be done. If you don’t know what that means DON’T TRY IT, PERIOD.

However since PVC pipe is a known for hobby and home made ROVs I will follow their lead. however I am not happy about using re-purposed bilge motors for thrusters; and am sure I can come up with something more graceful.