In The Tank

While certainly speaking to my lack of posting over the last few months, what I'm talking about is a quick snapshot of the new ballast tank actuating mechanism I've worked on over the last few months. Really, not worked on is more like it; a few several day spurts of concentration followed by prolonged inactivity.

Below is the general layout of the new system. The Lexan tube is new, purchased from Small Parts, Inc. They carry short lengths of 3" OD. The stock D&E Propel tank was modified with a new barbed fitting for the gas hose and cleaned and painted. The ballast tank is elongated by 3/4" to add reserve bouyancy, which has always been marginal in my LA. The pass-through tube is of slightly larger diameter to allow more room for the wires. It is glued in place to eliminate leaks and o-rings. The servo is now mounted over the battery in the forward compartment and drives the linkage via a rotary seal.

The brass control shaft passes to a bearing in the back bulkhead for stability. The servo, with metal gears, turns the shaft which rotates the control arms to either vent the tank or hit the Propel blow valve. The vent valve for the tank is not shown but was machined down from a stock Schrader valve. It is screwed in upside down so the arm pushes the pin up and opens the vent -- just like letting the air out of a tire.

As you can probably tell, the mounting tab for the aft bulkhed interfered with the rotation of the arms. After much deliberation it was decided to remove the tab and go with three screws to hold the aft bulkhead. They are basically just to hold everything in place and it shouldn't cause any problems.

Installing the blow valve and arm are the last steps before final assembly. Then it's off to the pond to test things out. Once again, little of this would be possible if not for the kind assistance and expert advice of Gail Phillips. The basic design is modified from his original work.

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Ballast Tank Blow Up

Since the Sun N Fun run I've been working on a major redesign of the ballast tank mechanism which goes in my 1/96 scale boats. I could not get it to blow in College Station and the servo seal has leaked repeatedly. So the time has come to replace the head and handle on my trusty D&E Miniatures axe.

After some disassembly, I found the tank would not blow because the Propel tank's internal discharge tube was plugged. The external fitting was removed and silver soldered closed. A new brass barbed fitting was installed on the end and silver soldered.

Cracks in the Lexan were also discovered around several screw holes so I purchased a new 3" Lexan tube from Small Parts, Inc. They sell Lexan tubes up to 3" od in 24" lengths. This is great because most other places you have to purchase an 8' minimum. Unfortunately, 3" is the largest diameter they carry.

Borrowing heavily from Gail Phillip's modification of his original D&E WTC-3.5, I sketched out the modifications I wanted. With Gail's assistance we turned a new 3" bulkhead master from which I created a mold. Four new bulkheads were cast and I headed back to Gail's where we turned the o-ring grooves on his lathe. I spent the better part of last Saturday marking and drilling holes in the cylinder to mount the bulkheads and tank. I also took the opportunity to lengthen the ballast tank by 3/4" in order to increase the reserve bouyancy for my LA model.

The blow/vent servo has long been a source of leaks so I decided to mount a mini servo on its side in the forward compartment over the battery and employ a radial shaft to activate the vent and blow mechanisms mounted on the after ballast tank bulkhead. The radial motion through the seal should greatly increase the watertight integrity. The diameter of the pass-through tube between the bulkheads was also enlarged slightly to allow the passage of the additional servo lead to the aft compartment along with the battery and speed control leads.

The result should be a much more efficient system, leak free, and maintainable in the field. Pictures will follow as things come together.

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