Understanding Stability and Buoyancy in ROVs

Fred DonelsonBob Richards

Jim Fannin

When you think about getting into a water craft, there are at least two major factors that you consider …

Most folks would like to ride in a craft that

• Doesn’t tip over (is stable)• Doesn’t sink (is buoyant)

When designing and building an ROV, we want the same thing:

• A craft that is stable and doesn’t tip over

• A craft that is buoyant enough so that it can be maneuvered easily up or down without using too much energy

So a very simple but important question is:

How do we make things float?

to find out …

So at least two factors are important to consider for

buoyancy:

• Weight (mass x gravity)• Volume

So, based on these two factors …

Would a kayak float?

Click on the picture at right to

find out!

Yes … provided the conditions were

right!

Now when things are sinking, rotating or floating, that most likely means some physical forces are

involved!

So click the link below to find out the mathematical calculations

relating the forces of buoyancy and the forces of gravity

http://www.youtube.com/watch?v=woIct8d6j_8&feature=relmfu

Of course, watching someone else do these

calculations isn’t as good as actually playing with

them yourself!

Now go to this link Read the instructions, watch the demo, and then play with the simulation until you have a good understanding of how changing volume or changing mass affects the interaction of the forces of buoyancy and gravity!

Think you have it now?How much weight can your ROV

hold without sinking?

Watch this video demonstration using a plastic cup as a simulated ROV!

http://www.youtube.com/watch?v=HTMwM81J48M

Stability of an ROV is affected by the distance between the center of

gravity (Cg) and the center of buoyancy (Cb)

Could you build a simple craft and illustrate this principle like in

this clip?

Can you come up with a general “rule” that would ensure that your ROV would always remain stable

and not tip over?

(Hint: think relationship between Cb and Cg)

Think you have this buoyancy/stability thing down?

Take a few minutes and click on this guy to see!