R/C Naval Combat

Posted By RichelieuBB on 16 Jun 2010 01:15 PM
It might be a good idea to raise the pump off the waterchannel floor a little. Although the screws on the pump do lift it a little, I've found the pump seems to pump more when it is at least a 1/4" up.

Thanks for the suggestion.  The mounting rails do hold the pump a little bit off the bottom, but it's only about 3/16", so I'll add a spacer to increase the distance a little.
 

I've started to work on my superstructure since the hull is mostly done.  I started by cutting the major pieces out of EPP foam, which is a rubbery foam instead of being brittle.  The model airplane guys use it to make very crash resistant planes - after covering it with packing tape, they do full contact combat.  While I had high hopes that it would be BB resistant, when we shot tested it the BB wasn't even slowed by a 3/4" piece.  So I'll have to figure out what I'm going to skin it with. At least it's starting to look more like a ship.

Posted By Kotori87 on 17 Jun 2010 02:05 PM
Looking good so far. How do you plan to arm it?

Right now I have a 75 round cannon for the rear, and a 50 round cannon for the front.  I figure that to start with I will mount the 75 in the rear and take it out for it's first combat.  Then after comparing my speed and maneuverability with the other ships, I'll determine if the 50 goes in the front or back.  But the guns are on hold right now waiting for my Clippard order.  I ordered my valves and solenoids two weeks ago and have nothing yet.  I could drive to the Clippard factory in about an hour, so it's rather frustrating.

 

After working on it all week, I finally got my pump control circuit working.  I threw away at least 4 designs and one circuit board trying to make it work.  This electrical stuff is tough for mechanical engineers like me. The circuit allows for the use of an ESC to control the pump, without taking a radio channel, and it includes a sensor circuit to run the pump only when there is water in the ship.

Basically, I took a 555 timer IC and used it to generate the radio pulses that an ESC would normally see from a receiver.  When there is no water, the chip generates a 1 millisecond pulse, equivalent to throttle off.  When water bridges the contacts, the resistance in the circuit changes, so the pulse jumps up to 2 milliseconds, equivalent to full throttle.  On the board I have two potentiometers, one sets the low pulse and the other the high pulse.  This way I can make sure that the ESC will see the proper throttle down pulse and arm, but if I do not need full throttle to meet my pumping volume, I can dial it down to exactly what I need.

I know this may seem like overkill, since there are a variety of pump controls out there and you really only need one basic switch to make a pump work.  However, I plan to build a 1:144 Gearing destroyer in the future and I'll need everything light, small, and with low amperage draw. To get this, I'll need to use a brushless motor and you have to use an ESC with a brushless motor.  So that's why I developed the control circuit.

Posted By djranier on 19 Jun 2010 04:27 AM
What kind of water did you use to test the bridge circuit? Tap or pond? Since water itself is a great insulator, the resistance will be different between the different types of water.

I used water out of the reverse osmosis filter in my house. I figured that it has the least amount of dissolved electrolytes, so it should have a higher resistance than pond water.  Of course, the final test will have to be at the pond.

 

Posted By Tugboat on 19 Jun 2010 07:38 AM
Cool idea! Is it resistance that changes, or capacitance between the probe tips? You are bringing some really useful skills to the hobby

The circuit is measuring resistance between the tips.  The probe circuit is not my design, but from a post on this site.  It consists of a darlington transistor and a resistor to generate a signal.  All I did was incorporate that into my timer circuit.

 

I have started work on my turrets and guns now.  The plugs for the turrets are partially finished, they have been sealed and a second coat of epoxy put on.  Now I just have to sand them down and wax them up so I can create the mold.  Here are the plugs as the mill is just about finished.

Between epoxy coats on the plugs, I'm working on the barbettes and gun mounts.   Originally, after looking at some other guy's mounts, I was going to mount the barrels and let the rest of the guns hang down.  However, when I sized up my barbette (1 1/2" pipe), it was too small to mount the guns by the barrels, so it was on to plan B, using the 90 degree fitting to mount the gun.  I put the 90 degree fitting in the lathe and turned down the bottom thread to 3/8" and then threaded it 3/8 - 24 so that I had a straight thread to work with.  Next I needed a base to mount the guns to, so I cut a plate to glue into the barbette, which you can see below.

The guns are mounted on a 1/8" aluminum plate which is cut to fit into the barbette.  While I did not really need to mount two guns per turret, I decided to see if I could do it, giving me the option of dual rear (or front) guns.  I was able to just barely fit two guns into the 1 1/2" pipe and keep the scale spacing for the barrels.  Here are the guns mounted on the aluminum plate.  The thin nuts came from my local electronics surplus store - they have gobs of them at $0.04 each.  The nuts did protrude a little from the mounting plate, so I had to grind off a little of the nut to make them fit.  But at 4 cents each, I can use a new nut every time I work on the guns.

The gun mounting plate is attached to the base within the barbette with two screws.  An additional screw - the nylon one - gives me elevation adjustment.  After setting the elevation, I just tighten down the two metal screws to lock everything in place.  Here you can see everything put together - clearance over the next turret is going to be tight.