R/C Naval Combat

My next project is building a Gridley destroyer. I've been looking at building a destroyer since I started looking at ships, but initially I thought I would build a Gearing, since it was larger. Then, after I had completed my Roanoke, I was looking at destroyers and noticed that there was a whole bunch with dimensions exactly 1/2 of the Roanoke. So the light bulb went on - if I built one of these smaller destroyers, I could just scale the Roanoke drawing by 1/2 and use wood 1/2 the size, so no drawing work needed. Eventually I decided to go ahead and make a new drawing for the destroyer, mostly because the Roanoke didn't have the two deck levels I needed. So the idea of doing a 1500 tonner destroyer stuck and I started working on it. It will of course be very challenging to build - not only is it small with little room for equipment, but it also needs to weigh less than 2.25 lbs. But if I can make it work, it will also be very hard to hit. So, since weight is paramount, I started with an estimate for each component:

I started by cutting out my ribs, keel and subdeck. I planned on using a 1/16" deck, so I also cut out a reinforcement to glue to the bottom of the deck. The first attempt was too heavy since I used 1/4 ply for the keel and subdeck:

My second attempt on the hull came out much better.  I used 1/8" wood for the keel and subdeck this time.

There is no such thing as 1" below waterline on this ship, the hard area stops at the 45 degree point on the hull, which is right above the bottom of the ship. I sheeted the bottom with 1/32" ply. 

Once the sheeting was done, I cut out the center of the ribs and most of the keel to give myself more room inside the ship.  At this point I'm ready to glass the bottom and it weighs in at 3.7oz.

I am slightly worried about the motor mount rib. I cut relief holes on the bottom so water can flow past the rib, but if the holes are not big enough I could end up capsizing. The rib is mostly solid because it will be one side of my gearbox.

The ship is 28.5" long

I have some of my components picked out, others I will have to develop.  Power will be an Axi 2208/54 brushless motor geared 2:1 to the props.  Power will be a 2 cell 2000 mAh Lipo to start, but I think that I may go to a smaller battery if the amp draw is low.  The motor will be controlled by a Castle Creations Sidewinder Micro car speed control.

I'm going to have to develop a modified gun to meet my needs.  My gun will need to be about 2/3 the weight of the normal gun, and needs to get ~60 shots out of a 12 g CO2 cartridge.  I have the 12g adapter and a Strike Models lightweight fixed regulator.

I know I may not be able to make the gun I need, so I have a backup plan.  This is a 15 round spurt gun.  The brass cylinder is a 2.0 cuin accumulator good for one shot. I just fill it up to 150psi - no liquid CO2 or regulator needed.  The whole setup weighs in at 4 oz.

I'm also working on the superstructure and accessories.  Here are the forward turrets with single 5"/38 guns.  The picture shows the plug (white), a raw turret right out of the mold (yellow) and a finished turret.  I used a two-part silicone to create the mold, which turned out to be very easy compared to creating a rigid fiberglass mold like I have done in the past.

Because the mold is flexible, and doesn't stick to anything, you don't need to worry about draft angle or release agents.

Posted By Gascan on 17 Feb 2011 02:48 AM
Thanks for posting your back-up cannon plan. Seeing the MEV Miniature Exhaust Valve jogged my thinking. It may be a little while before I can get my hands on the particular exhaust valve I need, but this may help make big gun destroyers a bit easier.

I wish Clippard had an exhaust valve that was between the MEV and J-series exhaust valve.  You can see the relative sizes below: From left to right is a MAV-3, MEV,and  JEV which flow 6 SCFM, 9 SCFM, and 58 SCFM respectively at 100 PSI. By adding a coupler and plug to the JEV as shown in the picture, you can create a volume chamber of about 0.15 cuin.  That volume is enough to propel a BB to 200 ft/sec with a straight 4.5" barrel and no o-ring.  However, when I added a 90 degree bend it dropped the speed considerably and I also had no magazine connected.  It has potential, but at 2 oz for the JEV I don't think it will work for destroyers.  Oh well, more development work needed.

The Gridley is only 3.0" wide, compared to 5.75" for your Indiana. The full load on the Indiana is 11,688 tons, so your full load weight is 11.7 * 0.75 or 8.75 lbs, plus as a class 3 you can add up to 10% for a max weight of 9.65 lbs. I'm allowed 2.66 lbs on the Gridley, but the ship doesn't have enough volume be that weight and still have a 1/2" of freeboard.

I draw up my parts in CAD and then cut them on my CNC mill.  It's cheating I know, but I find cutting ribs very tedious, and I have paid my dues over the many years before I got my CNC machine.

I wasn't really sure how well the water putty would hold up to BB hits, so I did some test shots today. As you can see from the piece on the left, the BB definitely puts a mark on the casting.  As long as the shots are not in the same place the damage was similar, but once two or three hit close together the casting shattered.  The turret on the right is made from the water putty that was mixed with 50% microballoons. The BB penetrated deeper as you might expect, and since it was near the edge there was spalling.  So overall not as resistant as solid epoxy would be, but since it costs so little I'm going to keep using it and see what happens on the pond. If next year is anything like last year, all my stuff will get shot off and end up at the bottom of the pond, so I'm not going to know if it survived the hit anyway.

I think that's a good idea.  I already have a can of tool dip for my servos, so I'll cast up a couple of targets and see how it affects durability.

Mikey had a build session today and I made further progress on the Gridley.  I had already finished the bottom of the hull and glassed everything, which only added 1/2 an ounce.  Today I made the decks out of 1/32 ply and also cut the gaskets out of craft foam for each of the hatches.  I'm not sure how waterproof they will be, but hopefully they will at least keep the water from from flooding in when the deck goes underwater.  I cut a groove in the subdeck for the gasket to sit in, leaving about 0.01" sticking up to allow for some compression.

I also got the shafts installed, 3/16" aluminum tube, and the rudder made.