Thanks for the tip on Hobby Lobby, I was finally able to make it there this weekend and check out what they carry. In addition to the regular Alumilite resin, they also carry the two-part foam so I picked some up. I think I will re-do most of the above deck molds in the foam. I should be able to save 1 - 1 1/2 ounces. That amount of weight would be insignificant on most ships, but it will be important for the Gridley. Below you can see the torpedo tubes, the one on the quarter is regular resin and the other one is made from foam. There will be four of these on the ship.
Just wondering if you ever finished this? I think a smaller prewar destroyer might be the next ship I want to build and was interested to see if you had finished or made any more progress?
I have not really worked on the Gridley lately, too busy with other kits I guess. I only have about 4 weeks before our last battle so I'm not sure if I will get it on the water this year. I did order some 3/4" props and a micro pump from BC this week, so I should at least the equipment I need to get it running.
mike, was looking at the surt gun design you showed earlier. did you delveop this and is it operational? think you said holds 15 BBs. does it require a O ring, looks like it does. also, how do you charge the cylinder/ have a k class cruizer and wont to convert it to two spirt guns. so could use some advice thx joe
RC, You should try one of these little pumps in your Gridley. That is if your running 12v. http://www.ebay.com/itm/25072272277...1423.l2649 Steve
With the other work posted on small destroyers, I have been inspired to get some work done on the Gridley. I've had the pump designed for 6 months but never got around to cutting it out. The pump has a 1/2" diameter aluminum rotor and is powered by a small outrunner. Tests in the sink show that it will pump 3/4 gallon per minute at about 80% throttle. Weight is 0.8 ounces, including the speed control. I've gone through 3 iterations of the drive train. I started with one motor turning a 4 gear system and decided it was too complicated. Then I built a gearbox with just two gears, one driven directly by the motor. It vibrated a lot, so I went looking for individual motors. I settled on the Himax 2208 - 870. The two motors together weighed the same as the gearbox but are much quieter. Each motor drives a 3/4" prop through a 1/16" flex drive. After a lot of experimenting with these flex drives in my PT boat and small convoys I am sold on them. They are lighter and easier to work with than solid 1/8" shafts. I have also installed an HS-55 servo, using a small custom pulley on the servo and rudder post to connect them together. All the parts together right now weigh 22 ounces. That's with the 12gram cartridge adapter and regulator, but without the gun, valve, and internal armor. Overall I'm pleased with the weight and think I can make my goal of 2 pounds. The hull has been waterproofed and is ready to sheet. With the weather predicted to be in the 50s this weekend I might be able to get the sheeting done.
Hey Mark, what Kv motor are you using on the pump? Also, I assume you found a source for the motors cheaper than $40 each...
I got a slight discount on the motors because I'm friends with the owner of the hobby store, but you are correct they are $40 each. The Kv on the pump motor is about 2400 - 2500. It's a hand wound motor and I need find my old test data to get a more accurate number. The pump was making the 3/4 gal/min at 14,000 RPM. So at 6.6 volts I could use a slightly lower Kv, but I probally won't change since I have a little headroom left with this motor.
Awesome build Mark!! I am always impressed with your hulls..... you have to pour a ton of time into those. Your little pump looks great.
This is the prototype of the pump, so it is a long way before it's ready to sell. I would probably not sell them myself, but I would share the design for those with their own CNC machining capability. The pump has three basic parts. The base is machined with a simple volute to collect the water and send it to the outlet. The next piece is the top of the pump, a flat plate with holes for the motor mounting bolts and the exit tube, which is 3/16". The 2-56 motor mounting screws go through the top plate into the base, attaching the motor and also keeping the pump top and bottom together. The impeller is 4 blade design machined from aluminum. It is attached to the motor using retaining compound. I place a piece of paper between pump top and the impeller and then glue the impeller to the motor. When the glue is cured, I rip out the paper and am left with a nice 0.004" gap. The gap between the impeller and the bottom is larger, but still pretty small. Here's the drawing. Note that the impeller is machined from bottom and the base is machined from the top, so when assembled the rotor blades are in the right direction, unlike how it's shown here in the drawing.
I make my own flex drive, it's not that hard. I got most of the information needed to make the flex shafts from the Rumrunner Racing forum for fast electrics. Search on flex drive or music wire drive and you will get a lot of information.
Well, I had a compact magazine printed by Shapeways for the Gridley. The idea was to have a tight coil to hold the 50 BBs. Because the material is basically nylon, it would be light weight and compact. Here's the first version: When the magazine first arrived, I thought that I had been cheated - the magazine was solid, with no coil through the middle. On closer examination, I discovered that the magazine was not fused solid, it was just filled with powder. So with some thin wire I cleaned out the coil. Unfortunately, the BBs still didn't fit in the magazine. I had made the diameter of the coil 3/16, which is usually enough, but it's not enough for the 3d printing process. So I redesigned the magazine, made the diameter of the coil 7/32 and made it bigger and thicker. Here's the updated magazine along with the original and a low pitch prop for my yard oiler. This time, after cleaning out the powder, the BBs went all the way through the magazine. Plus, it held 54 BBs, so it was the right length. Weight of version one was 1/3 ounce, while version 2 is about 2/3 ounce. Still pretty light though.
With the magazine in hand, I was motivated to work on the gun. Two key requirements for the gun are lightweight and low profile (p> I ran a couple of BBs through the gun just to verify its basic function. Tomorrow I'll conduct full pressure checks and see if it holds up.
