1:72 Los Angeles

[spankey]

So, I went back to the drawing board with the battery...I dug up an old 12V, 2.5 AH battery I had lying around. It weights 2.5#, so more reasonable than 6 #.

I would prefer to get everything dry in a forward compartment, BUT I've been doing this boat for over 2 years now, and Its the only obstacle in my way of getting another boat.... the 1:72 Skipjack, so I'm going to wait on fixing up a dry compartment until I get that Skipjack.

I did some trimming yesterday in the kiddie pool, and discovered some leaks...

One of them, probably the most concerning was a slow leak from the pushrod seal on the Ballast tank bulkhead. I put some silicone on that pushrod, and we'll see how that works.

The other two leaks were embarrassing...there are four (4) pushrod exits on the 3.5" WTC, and I'm only using two of them. Last time I checked, 4 minus 2 equals 2, which leaves two pushrod exits still open. Yup, there was water in the enginerooom.

I'll deservedly get my pee pee schwacked by the boss for doing that, but I guess live and learn. No real damage done.

Below are pics of the battery location, and the pushrod exits, NOW PLUGGED!

[He Who Shall Not Be Named]

And I'm most grateful John finally convinced me to provide a forward dry space in the re-designed 3.5" SD's, in which are now housed the battery -- a much more user friendly and rational design than my initial one which put the battery in the wet.

John Slater is my most reliable and informative Beta-tester! Much of the current crop of SD's feature elements suggested or re-designed by guys like John. The products I produce are very much a collaborative activity between me, Mike, and our experienced customers. The soon to be released line of 3" SD's is an example of such cross pollination.

M

[Slats]

I concur with advice above - big problem I have learnt to avoid from the masters in this game is keeping weight down.

Too much weight =Too much mass momentum

Mass momentum is basically the ability of an object to continue under its own momentum on a straight track. The higher the weight - the greater the mass momentum that needs to be overcome to turn the boat. In short - heavier boats don't turn as well as lighter ones.

My first subs used heavy wet area SLAs - yes your sub will work this way, but a better method in my experience is adopting a dry space for a Nimh or Lipo. You could see if you could buy a simple cylinder section from Caswell's to achieve this to work with that old Subdriver you have there.

A conversion I did is found here: http://forum.sub-driver.com/showthre...=Collins+class


Apart from the higher weight issue that a SLA means, you are also fighting with the COG.
COG should be achieved dead centre under the ballast tank. Here the SLA weight forward of that location makes it a hard task to achieve.

Finally I have had numerous sealing methods of external wires over the years. All work fine but longevity of these connections becomes a problematic issue.

For all these reasons I successfully convinced David to manufacture the 3.5" SD with a conduit through the ballast tank connecting a forward and aft dry space. This keeps battery weight down through use of LIpo / Nimh battery, connections are always dry. As for battery capacity I only use a 3AH nimh 7.2v I find the run time is excellent (about an hour).

Hope that helps

John

[He Who Shall Not Be Named]

4Ahr's is plenty, and like Mark said, too much battery!

M

[greenman407]

Im thinking that if you put that much weight in there that you would have to put a heck of a lot of foam in there as well to help your ballast tank float that much weight.

[greenman407]

Spankey, 6.1 lbs seems like a lot. Looking at what youve got there, youve got plenty of room for a battery WTC up front. Inside you could put a LIPO or a stick NIMH. Im sure that you could make the 6 pounder work.............
As far as center of gravity in relation to center of ballast tank Id start with 1" forward of that and just see how she handles. On my Albacore I had to play around with that, but thats only because I wanted to go fast.

[spankey]

Next Update,

Just soldered up a prop linkage from the shaft on the hull to our Most Esteemed Leader's WTC. As you can see, the WTC is presently positioned aft so that the Center of the Ballast tank is ~1 inch forward of the center of the boat (lengthwise). Thanks Admiral Greenman.

With no battery installed, the CG is somewhere near the aft 1/3 of the boat.

I'm planning on a 6 Volt, 14 AH Werker Gel cell, unless someone wishes to correct the abhorrent error of my ways. This cell weighs ~6.1 lbs, which should drive the dry CG into the forward 1/3 of the boat.

Is there a rule of thumb for where the CG should be in relation to the Center of the Ballast tank, which is positioned as stated above?

[spankey]

So I did what you suggested, and I've mounted bulkheads (tacked them down) for the WTC. See photos. The center of the ballast tank will be 1" fwd of the geometric center of the boat.
Next thing to work on is getting that CG slightly forward of the center as well, then trimming.

[greenman407]

I have always had good results with finding the center of the submarine and putting the center of the ballast tank 1" further toward the bow.

[spankey]

Question, does anyone with a little more experience than me have a good way to locate the WTC in the hull, and have the ballast tank properly positioned for a good trim?

Thanks, Daniel

[spankey]

Thread not dead, I'm on active duty, so its been hard to have time to work on the boat. Finishing truck clutches, etc on the weekends... you guys know the drill.


I should be back on this in a couple weeks, so Standby. Next up will be loading everything into Mr. Merriman's WTC and crossing my fingers that I've put it all in there correctly...!

[Tugfan]

Thread dead?

[spankey]

After a LONG hiatus, I've gotten back on this project. I'm Active duty at Flight School, so for those of you aviators out there, you know this takes most/all of your time.

Just putting together the Subdriver that Mr Caswell and Merriman sent, it was the last of their old 3.5" units, and I'm very grateful to have it.

Question....As you can see in the picture below, I'm starting to put stuff onto the rear motor tray, and wondered if anyone had any advice about preferable locations to put stuff.



I just bought a new 50MHz Lepton Receiver, so when that gets here, I am going to put that on the most forward tray shown in the photo. Any issues I should be concerned with about where those servo's and the speed control is with respect to the motor?

I'm planning on putting the level keeper (just bought this from Caswell) on the bottom of the tray, right below the two servo's. Any problems with this location?

Dan-

[spankey]

I just received my 3.5" Subdriver from Caswell this afternoon! Excellent! Actually it was the last of the 3.5" units (I think), because I think they're changing the product line-up, BUT as expected, Caswell and Mr Merriman delivered! Since it was the last unit, and they didn't have any more units in kit form, they sent me one they had that was already assembled! Thanks alot, I really appreciate it!

These guys are awesome. This next week is going to be busy, but I am hoping to get this thing into the boat soon! More to follow....

[spankey]

Yup, that worked. That Oilite responds pretty well to the file....doesnt get too scarred up.

I didnt wallow too much out of the bearings, but enough. Also, loosened the retaining nut on the prop, and re-positioned it. The prop was pressed up too tightly to the extreme stern of the hull....that was part of the problem also.