Building a pair of Deutschlands

Do you plan on posting the cannons as an 3d printing file?

 

I guess I should. I'm about to go on leave, but I'll put the files up when I get back.

 

I love the work that you did on the Deutschlands

 

The bow guns are Greg's design. The stern guns (twin low-profile BICs) are my own. While I cannot post Greg's design without permission, I will certainly post all the parts for my own design, along with comments and printing tips. For now, though, back to packing.

 

I woud' mind the stern ones they look GREAT☺

 

The stern cannons interest me

 

OK folks, big update time. Just got back from the battle this weekend, and I've got a lot to report. Both Schleisen and Schleswig-Holstein saw heavy action, getting sunk a total of five times. In every case, the ships came roaring back afterwards, with no problems due to extended water immersion. I treated this battle as an extra-vigorous sea trials, so there was far more risk-taking and experimentation than sensible combat tactics. I chased the cruisers, swapped sidemounts with the big boys, ran around with heavy damage, and generally found out the hard way why most folks don't do those things. I got a solid feel for the ship's handling, and I can say that the Deutschland class is a very nimble boat. Quick, snappy acceleration and a tight turning radius in a very small package makes for great fun. The single shaft/single rudder combination makes it impossible to back up straight, and gives it markedly different turning in each direction. The single sidemount can be very effective when set up right, and the twin sterns and fantastic turning are a joy to use. Its overall handling characteristics seem very similar to the famous/infamous Sopwith Camel, nicknamed the "cross maker". Tons of personality to take advantage of, and very unforgiving of mistakes. Like the pilots who flew the old wooden kites, anyone who sails a Deutschland into combat will either get an Iron Cross or a wooden cross.

One undesired characteristic was a tendency to rock heavily while turning, with a fast period and a large travel. The ship's righting moment is quite nice, but the large thrust low on the ship, suddenly being redirected sideways, made it seem rather tippy while turning. I hope that installing bilge keels will reduce that undesired characteristic, and I recommend that modification to anyone else building this ship. Other issues included the poor seal around the superstructure and the long time to remove the superstructure. Despite using four screws and an electric drill, the time required to close up the ship for combat was excessive, especially when the screws didn't quite line up. These will be replaced with magnets. Also despite using four screws to tighten down the superstructure, an excessive amount of water was able to wash in through the gaps. This will be dealt with by adding a railing around the inside of the deck, both to keep out water and to align the superstructure and magnets. Expect further reports and pictures after I try these.

An unexpected benefit of the Deutschland class's excellent acceleration was that I could often catch larger, heavier ships in a short sprint. While the saying "don't chase the cruiser" is well-proven, I was on several occasions able to catch a cruiser from a dead stop with my sidemount and unload a significant portion of my ammo into it. I also failed several times, and got shot up because of it.

As an experimental platform, these two boats are demonstrating top-of-the-line technology such as laser-cut snap-together hulls, 3d-printed superstructures, BC's fantastic new fire control boards and high-flow solenoids, and two very different high-performance 3d-printed cannons. Despite the abundance of new technology, both ships entered every single sortie in nearly perfect condition. The only significant pre-battle failure was Schlesien's starboard stern cannon on Sunday, which jammed and was unplugged before the sortie. Further troubleshooting is required.

Once in combat, several other major failures showed up. First, the small restrictors of the 1/2-unit pumps proved extremely vulnerable to debris. Schleswig-Holstein sank in the very first sortie due to grit partially blocking the restrictor. Later on, Schlesien sank due to a sliver of balsa getting stuck in the restrictor. A more effective filtration system is required, and will be installed prior to the next battle.

The next major failure was the armor. Despite using ultra-soft competition grade balsa, something went wrong during the preparation process, making the finished product dangerously brittle. When hit close to perpendicular, shots left very nice round holes. When hit closer to parallel however, shots tended to tear very nasty chunks out. This nasty habit of chunking directly caused two of our five sinks this weekend, and forced us to call "on five" early in the fight several times. This bad habit got worse the closer we were to parallel, so the normal defensive response against triple and quadruple sterns actually made the damage worse. As soon as possible, both ships will be resheeted in balsa using 3M Super 77 contact adhesive to attach the silkspan. The good news is that I made patterns of each section of sheeting last time, so this time it should be a simple matter of tracing and cutting.

Perhaps the biggest success of the battle was the 3D printing. The 3D printed cannons hit hard most of the time, and the 3D printed/laser cut superstructure got shot in every imaginable location and came away with negligible damage. Take a look:

The worst of the damage from the whole weekend: two funnel caps lost, a cracked splinter shield, and a broken armored mast. The mast stayed in place due to the mast tube running through it, and was not lost overboard.

The bow turret took a hit, I think. it's hard to tell. There's barely even a dent. Also note the shattered balsa that sank me during the last sortie.

Note many hits on the casemate. If you look closely you can also see a hit on the upper superstructure which knocked a gun shield loose, but failed to knock off any parts.

The bow took quite a few hits. Note one solid hit on the shield, and another one on the starboard side gilding.

 

It was very nice to meet you two. You guys built awesome little predreads. I and many of the northern guys have never seen a 3d printed cannon actually function, and yours worked well enough that it was a hot topic of conversation for the road trip home.

With some tweaking, those boats will be nasty little sluggers. Get some screen on those pumps to keep them clear of debris and you'll have a much easier time surviving damage.

 

Very nice! What material are you using on the superstructure, and how thick?
(I know, it's probably earlier in the thread, but I haven't read that yet)

 

wow, look a how much damage has been done

 

It's to be expected. Both of those boats took that much damage probably 3-4 times over the weekend. It gets patched up, right back out into the water.

 

I'll throw my "WOW" in here as well. Very nice job building the ships. you did a fantastic job documenting your builds along the way for the rest of us to follow along. looks like we have another wonderful class of boats available to the hobby. Thank you for sharing! (thank you also to Nick and Greg for all your work making these kits, When is the next kit run?)

Craig

 

I've been doing some experimentation with propulsion. My current motor, one of the 6V BC motors, requires significant reduction to get the ships down to speed. Currently over a 2:1 gear ratio and about 45% throttle to hit the 28-second mark. I'm not happy with that, so it's time to experiment. I got a phototachometer, so I could measure the speed of the prop. With my original setup of dual drag disks, 1.5" 6-bladed prop at 20* pitch, I measured approximately 6200 RPM out of water. No idea about in water since the phototach isn't waterproof, but I'll use that as my target RPM. I bought a new set of 550 can motors, this time for a higher voltage. The new motor with the same reduction ratio at 100% throttle measured about 5100 RPM out of water. That's a little slower so I'll have to change my gear ratio before the battle but that won't be hard. I currently have over a 2:1 reduction. The real reason I'm doing this is that eventually I want to swap over to a brushless drive. Kinda hard to call this project a marvel of modern technology if I'm still puttering around with brushed motors, right? Actually I just want a shorter, more compact motor to make the pump fit better. I think I'll do further research at the next few battles to see what kind of props, RPMs, and pitches various boats need to reach their target speed.

In other news, I think I solved an issue with my stern cannons. Their 3d-printed pistons had a bad habit of getting stuck in the up position, and refusing to feed in the middle of combat. Despite acetone smoothing and polishing each with a file, they still got stuck about once every 5-10 shots and required mechanical agitation to reset. Sometimes I would end a battle with 30 rounds left in a magazine, thinking I'd been out for minutes. Those of you at the last battle in Statesboro might have noticed this bad habit, and my tendency to fire only a few shots at a time. Today I took a Strike Models injection-molded piston and cut it down to fit, then cleaned up the tip with a file. After that I ran three magazines through it without a single misfire. I tried single shots, I tried short bursts, and lastly I ran one full magazine as fast as I could pull the trigger, laughing like a madman all the while.

 

So if my math is right, and man I'm bad at math, and assuming your throttle is perfectly linear from 0 to 100%, you should be seeing almost 28k RPM (27,555) at the motor shaft at 100% throttle. You're operating at 45% throttle, so say 12,400 RPM motor shaft. A 2000kv brushless would be about comparable to what you currently have in there (before you stepped to a slower motor). I'd suggest something lower in the KV band to get your throttle endpoint closer to 80%. A 1000~KV motor would probably be ideal, if my math is close. Always best to aim high, you can always endpoint the top speed down but its hard to make more speed from less.

This is all assuming the boat is running 6v. If 12v, half the KV recommendations.

 

I'm actually at 7.4v, not 6v, but yeah something around 800-1000KV is what I'm thinking. Still not sure if it's worth it, since most brushless motors use ball bearings that are susceptible to rust. One more maintenance item on a ship that's supposed to be as low-maintenance as possible.