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Ballast Systems - Variable Displacement Cylinder

R/C Submarine modelers

Postby Chuck Davenport » Mon Dec 01, 2003 1:00 pm

I teach a manufacturing class in high school and encouraged four of my students to take on the project of designing and building a variable displacement ballast cylinder. Deceptively simple, the device uses a 12volt linear drive, which actuates a piston. Variable displacement causes the cylinder to rise and sink in the water. Current draw during the extension cycle is near 1A (bad news), but (good news) the cycle time is less than three seconds from negatively to positively bouyant. Neutral bouyancy is easy to attain. As I write this, the cylinder is in a water tank, testing the cylinder for water-tightness with the O-ring seals we made in class.

This is a proof of concept design. From there, we will move to the functional design of a system comparable to the WTC...without the need for compressed gas!

Thus far the main limitation is diameter. This system is suitable only for larger diameter hulls. Piston diameter is 4 inches, which is the width of the linear drive. The drive gives us 27 lbs of force. Finding a smaller drive has been an unsuccessful challenge.

Look for a full report as soon as we submit an article to the SCR. The article will also show you how to do the buoyancy calculations...all done by my high school students.

Chuck Davenport

Postby Bob the Builder » Mon Dec 01, 2003 5:34 pm


What form of linear actuator are you using? How is it controlled?

Any info on the system that you could provide would be of particular interest to me for an upcoming project...
Bob Martin,
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Postby JWLaRue » Mon Dec 01, 2003 8:00 pm

Hi Chuck,

I am looking forward to the article. If there is any information you need regarding article submissions, please let me know.


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