I guess I did the water channeling before floating the ship because I didn't know any better. I think it will turn out OK for two reasons. The first is that I started with an estimate of all the component weights and where they were placed. This gives me an estimate of balance so I should not have a serious out of balance situation when done. The second reason is that the water channeling really didn't use much space (it's less than a 1/4" around the motors) so if I have to put ballast on top of the water channeling I can. I still have plenty of area to work with forward of the main water channel too. I'm using "Fluid Mechanics and Thermodynamics of Turbomachinery" by Dixon as my pump design source. It's at a high enough level that I can understand it. I'm mainly developing the blade vector diagrams with the formulas to get a decent blade and diffuser shape. I'm not even going to attempt to calculate the efficiencies.
Mark The build is looking great. Do you think you will be able to drop in at the WACO event next weekend? Mikey
you may want to drop by the library for the book I listed as well... It has a great deal on standardized volutes that work well in all sizes of pump, as well as design curves based on real pumps (apparently almost all of them fall on the same curves, at least the ones that work well). You will find that your pump looks radically different than standard combat pumps, if you go through the math for water. just keep in mind that if you do optimize for clean water, you will get a more efficient/powerful pump that is less tolerant of stuff getting into the blades. (see the karlsruhe rebuild thread for some impeller pictures, if I recall correctly) Another consideration you will find is that the math will tend to lead you to larger diameter impellers than you really want to do... it is hard to keep the open impeller aligned up properly for the more efficient designs out there, especially if one is just setscrewing to a motor shaft to secure. If you ever want to chat about pumps, I'd be happy to let you know what has and has not worked for me...
I'm making slow progress on the Roanoke. One step forward and two steps back. A week ago I had the prop shafts permanently glued in and I finally finished the drive dogs to mount on the 2.3mm shaft of the 380 motors. I also completed the drag props for the outside shafts. I even hooked up my ESC and had props turning. That's when the problems started. I found out my Tekin car ESC that I've had for 10+ years didn't have reverse. So I went down to Radical RC, which is a local hobby shop for me, and tried to find an ESC with reverse. Since they are primarily airplane parts, they didn't stock ESCs with reverse, but by chance they had a one Castle Creations Sidewinder ESC and at a good price. I was even more excited when I found out that you can control either brushed or brushless motors with the ESC by changing software settings. So I soldered my plugs on tonight and went to test it out. When I hooked it up, the motors immediately started running without going through an arming sequence. I assumed I had a problem with servo controller I was using, so I got another one and hooked it up. With the second controller I could change the speed of the motors, but not turn them off. About the time I discovered that, the magic smoke left the ESC. After much head scratching, I realized that I had put the motor plugs on the battery side of the ESC and vice versa. Rookie mistake, and I'm not a rookie when it comes to ESCs. So the ESC is ready to go out in tomorrow's mail for repair. When I get it and my 2.4GHz transmitter module back from its repair, I'll be able to finish the radio setup.
Have you given any thought to water protection for your ESC? Unless they're factory-waterproofed (epoxy-potted, not o-ring sealed), most ESCs don't mix well with water. As in, few drops of water = fatal. Many electronics, including servos and receivers, can be salvaged after getting wet if you flush them with alcohol, but none of the ESCs I've found can do that.
As a genuine ex-Navy electrician, and therefore a battler who has made lots of smoke come out of things like ESCs and electronic switches... waterproof it or stick it in a WT box Many things that one would THINK are okay with an occasional splash of water, aren't!
Funny how the boxes are called "water tight" not "water proof".....is it that they hold water in better than they keep it out?
Well the plan is to use a waterproof box for the electronics, but I have not selected one yet since I don't have all my wiring done. Does anyone know if there is a good thread on waterproofing servos? I've looked, but have missed it if there is one.
It floats!!! It doesn't have any leaks!!! Yesterday Mikey came over to my shop and helped my set up my guns and gave me a sheeting 101 class. I didn't realize that the MAV2s had an inlet and outlet and that they would leak if you hooked them up backwards. Of course I hooked them up backwards, so when I initially cracked the valve, CO2 was escaping freely. Fortunately, I had not glued the valves into the ship, so after a little re-work of the valve system everything stayed sealed. After a few minor tweeks, the guns were firing with reasonable consistency and velocity I had originally planned to sheet the sides with 2mm depron foam, but when I tested the contact cement on the foam it ate the foam. With my first combat two weeks away, I decided not to mess with figuring out the foam. Fortunately I had enough 1/32 balsa in stock from my airplane supplies to sheet the Roanoke. Attaching the sheeting went fairly quickly. The only problem I had was sanding a little too hard, so the balsa is really thin over a couple of ribs. Hopefully the silkspan will keep it all together. Once the sheeting was done I added a coat of grey for extra sealing and let it dry over night. It has some wrinkles and is a little wavy in places, but overall I'm very happy with my first sheeting job. The Roanoke now weighs in at 9 pounds, 9.8 oz with some of superstructure and a couple ounces of radio equipment missing. That means I'll have about 1 lb of ballast to work with to reach fighting weight. I took the ship out to the hot tub and it floated fine. After all this work, it is great to see it sitting there in the water. I left the ship in the water about 10 minutes and could not find any leaks. Which is actually a little surprising, since I had forgotten to put the grease in the stuffing boxes. I guess the shaft to bearing fit is tight enough to keep the water from coming in very fast. I marked the waterline and declared it a successful launch. Now to complete the fitting out.
I'm getting a few things done on the Roanoke each night. My first battle is a week away and I'm feeling a little pressure. This week I finished up the painting on the hull and put the grease in the stuffing shafts. I've also been working on the radio and controls. I built my radio box out of a bit of 1.5" PVC pipe, with a circuit board at one end to put all the signals through and an aluminum cap sealed with an o-ring on the other. In the radio box I have the receiver and two R/C switches, one for the motor reverse relay and one for the guns. You can also see the AnyVolt which up converts the battery 6V to the 12V I need for the gun solenoids. I tested the system and the guns fired fine. I got my pump hooked up and tested today. At first it didn't pump any water, even though it was running, so I pulled it out of the ship and saw that the impeller wasn't turning. Turns out the set screw had stripped its threads. So I re-tapped the hole 6-32 and put in a longer set screw with a little locktite. Hopefully it will hold. It's 98 degrees outside, so instead of going out to the hot tub for tests I did them in the house. As soon as the pump primed it shot a stream of water about 5 feet in the air (through a 1/4 pipe, no restrictor) and made a mess in the bathroom. But is was a successful test so I'm happy. I'm having trouble with my automatic pump circuit, sometimes it works when it's in the water, sometimes the pump started when I took the probe out of the water. Oh well, I don't have time to trouble shoot it this week, I'll just control the pump through the receiver. I did eventually get it calibrated to pump 3/4 gal per minute.
I finished my end-to-end control checks tonight, including sea trials. The drive motors were hooked up backwards of course, couldn't have a shakedown cruise without any problems. All the rest of the controls worked fine, so I'm declaring the insides of the ship ready for combat. I was also able to get my forward only ESC to work just like an ESC with built in reverse. The ESC is hooked up to a 5V DPDT relay that reverses the motor wires when it's energized. I have a second channel with a Pololu R/C switch that energizes the relay when it sees about 60% of stick throw. But then I used two programmable mixes so that when the throttle stick is in neutral the ESC is off, when I pull down on the stick the relay engages and I get proportional throttle in reverse. When I push up past neutral on the throttle stick I get proportional forward. The first mix mixes the throttle throw with the relay channel, so that below about 45% stick the relay is on. The second mix mixes throttle throw to throttle output, so that neutral stick is 0, full up is +100 and full down is +100. It took some experimentation, but I'm very pleased with the result. Here's what the final internal configuration looks like:
I've also been working on the superstructure. There are three platforms on each side of the superstructure for the secondaries, which are dual 3" guns. I thought it would look stupid to have empty platforms, so I started thinking about a simple 3" gun. Pictures of the full scale gun were not much help, because they just look like a bunch of different parts without any real distinguishing features other than the barrels. So I made up an outline and cut it out of 1/8 ply to see what it looked like. It was a little plain, so I added some random pieces of balsa to give it some depth. You can see the result below - good enough for standoff scale. Now I just need to make 5 more.
The Roanoke is now a combat veteran Yesterday I took the ship out for speed trials and things did not go exactly as planned. After the first run I smoked a motor, which brought an abrupt end to the tests. Fortunately, the second motor worked slightly and I was able to limp back to the dock. I determined that I was just pulling too many amps, so I put a pair of milder motors in. I also took some of the grease out of the stuffing boxes and added some end play to reduce friction. The combination of these changes cut the amps in half. I took it back to the pond today, and this time speed trials went off without a hitch. I loaded it up and went out for my first sortie. I didn't get sunk and even got a couple of hits in on the other guys. After two sorties, I had 28 hits on the ship, but only one resulted in water getting in, so I was in no danger of sinking. I'm very pleased with the performance of the ship, it accelerates quickly and turns great. I'll patch up tonight and be back on the water tomorrow. Thanks to all that have followed this thread, especially those who answered my questions. I need to thank Mikey and Phil for answering my hundreds of questions, without their guidance this build would not have been possible.
Your not done you will change things for at lest the next 2 years. Your on the water its all good Took me 2 years to get were i m happy with my ship. you will always see were you can get better. we call it the magnificent obsession
