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[Robert F.]

Hello all,

I am thinking of motorizing a small sub kit. Instead of using a ballast tank system, I am considering using a shifting weight (batteries) to change the angle of the boat, thereby submerging or surfacing it.

Does anyone have any experience with this kind of ballast system?

Rob

 

[Shipmate60]

If you search HMS Fearless on this site I believe there are some ideas to allow the stern to submerge.

Bob

[Patrick Henry]

Robert, if you check into the AMS (Association of Model Submariners) forum @ www.theassociationofmodelsubmariners.com and ask your question there, you'll get some responses. I know of at least three members of the AMS who have done just that.


Rich

[Davy1]

Yes. please do that.

(I have done this for 2 of my subs and it is much easier than you might think. My experiences have only been written up in the AMS magazine, though.)

Norbert Bruggens formula in his book is a good start.

David

[unbuiltnautilus]

Oh please tell us, I couldn't cope with having to remember ANOTHER password for ANOTHER forum, just for a simple answer. How big a weight for a six foot shark please?

[Subculture]

The weight of your finished fish could be anything from 5-50kg, so I don't think anyone is going to be able to give you a reliable figure.

But if you want a rough idea, try and aim for a moveable ballast of about 20% of the boats overall weight to enable really good pitch control (e.g. plenty of angle). Batteries or ballast tank are usually the heaviest items in a sub, and they tend to be linked to a servo connected to a sliding tray. This offers proportional control, some people use home made jack-screws, in a bang-bang fashion for one-off trim adjustments, although they can also be proportionally controlled using the appropriate electronics.

The heavier the weight, the less distance it has to be moved, and vice versa.

[unbuiltnautilus]

Cheers mate. I will be shifting water ballast in my Type VII, so will see how effective that is in altering trim. The water ballast is not designed to trim up or down by the bow, but could be useful to see the effects.

[Robert F.]

Thanks for all your replies and info, guys. 

Rich, I will also post the question at AMS. There is room for one more set of passwords and user names.... 

Robert

[gyronuts]

I used to have a 51" x craft built by Nigel Edmonds and it had 2x 6 cell 3300 nimh battery packs that moved by operation of a servo. It made trimming a piece of doddle. Bill

[Robert F.]

I used to have a 51" x craft built by Nigel Edmonds and it had 2x 6 cell 3300 nimh battery packs that moved by operation of a servo. It made trimming a piece of doddle. Bill

Any pictures available?

Robert

[Davy1]

Robert,

Have you posted on the AMS site yet? Because if you do you will probably speak directly with Nigel. (He does not post on here.)

Nigel has used the shifting weight concept on several models including his Holland (Now owned by Andy).

I used a shifting weight on my Holland also. I used a lead weight because  I was using LIPO batteries (so rather light to shift). The method works well with only the short throw from a servo ( as suggested by Norbert Bruggen's formula, mentioned earlier.)

I wrote about my Holland in a recent issue of the AMS magazine.

Good luck with the method.

David

[Subculture]

The Holland shifts the battery (a 7-cell sub-c NiMH pack) fore and aft about 25mm overall. The battery is held to an acrylic tray with velcro straps, and the tray is actuated by a standard Futaba servo- nothing exotic and it does it's work very easily. The proportion of weight being shifted is about 10% of the boats AUW, so you get a fairly good range of tilt.

It's possible to control the pitch of the Holland using weight shifting only, however it is a slow boat and for a faster model that method of control would prove tricky- anyone given it a go?

If you are using lightweight batteries- e.g. lipo- you could add some bulk by sticking some lead onto the battery, or the even the sliding tray, or perhaps consider making the tray from something heavy like brass plate. Another possibility is to shift the position of the ballast tank, although this will be dependent on the system being used, boats with a tank incorporated into the cylinder walls won't permit this option.

[Albion]

This is my ballast shifter, but it is used for trim, not to create a dive angle. Im using single piston tank, which is level at the extremes (full/empty) but can get out of shape in between these points, which is often where i want to be!

Last two photos shows semi submerged, the with ballast at its extremes. Its a dry hull, so yes it does need a big lump of lead. I probably need a little bit more weight in the bow

A123 LiFe batteries
 

[Subculture]

You've gone the other way- moving a smaller weight a longer distance, about 5" of travel by the looks of things.

[Albion]

You've gone the other way- moving a smaller weight a longer distance, about 5" of travel by the looks of things.

I changed from big lead acid batteries to the LiFe, so my starting point was the space previously occupied by the old batteries, and the weight difference between the two batteries. i extended slightly the front space which pushed the whole tech rack slightly rearwards in the hull. hence i probably need to re trim with some more lead up front.

Im using a Engel BTS to control it, which was easy to wire up, with the micro switch end stops. 

Also doubled the Amp Hour capacity on board :)