RE: 3dp u-boat My CoreXY is, of course, different from all the others. As an engineer I guess I can't accept compromises from others, I have to come up with my own. Anyway, since I'm far enough along I've started a build thread on Reprap forums http://forums.reprap.org/read.php?397,417806 Speaking of Rostocks, I think that you need to build one of these: http://forums.reprap.org/read.php?178,415436 The diameter of my coil magazine is 1 1/4" diameter.
RE: 3dp u-boat That's tempting, but my Pipedream project will produce a bigger print area with a more rigid structure. I'll post some pics of the 6" diameter proof-of-concept shortly. Carl and Eric saw the early prototype of the top plate, which I will find a pic of and post here...
RE: 3dp u-boat I apparently cannot edit my own posts anymore! In Chrome, it gives me a blank gray text window that I cannot alter (and doesn't even show the old post), and in IE it gives me a text window, but none of the buttons for putting in pics and other niceties. It used to work fine, did something change on the forums?
RE: 3dp u-boat After reworking the CAD file I was able to print a 50 round magazine. It is shown below with a magazine that I had printed by Shapeways.
RE: 3dp u-boat Good news!! Slicing it in Slic3r was the trick! It's not as convenient and easy as Cura but gives more control over certain elements that were crucial to success (like print speed during a bridging action)... In shiny brass colored plastic, I got a good printed magazine I will do more tonight after going to my niece's Christening (4-5 hours on the road, argh!) and do testing tomorrow!
RE: 3dp u-boat Very cool! No issues with pressure I assume? Can you also make the rest of the gun out of this material, or is it a combo of brass and plastic?
RE: 3dp u-boat Full-on pressure tests will be coming soon (possibly tomorrow if Brian K brings gas, or if I have some left). At this point, it's a combo of brass and ABS. I have thought about a fully printed cannon, or at least a mostly-printed cannon, but that will require some collaboration with someone smarter than I (like Mark). Obviously, with a printed cannon, we'd be looking at having to weld a cap over the bottom after the interrupter pin goes in. Chemical welding, mind you, with acetone. the breech would be tricky with a printed unit. Doable, but the tricky part would be printing good threads small enough to not be ginormous and thus impeding scale appearance. If we could make the bottom part all-printed (metal or nylon interrupter), I'd be pretty happy, because those brass tees are getting expensive.
RE: 3dp u-boat I remember a discussion a while ago about using a small air pump to blow ballast for a submarine. While interesting, it had the limitation of requiring a source of air to blow into the ballast tank, probably provided via snorkel, with CO2 from the cannon system as an "emergency blow" backup. I continued to research the topic, and dug up some much better alternatives. First, I found a cheapie toy submarine that had a working ballast tank for depth control. The Graupner micro U-16 uses a geared motor and a threaded rod to move a piston in and out of the ballast tank, sucking in water or blowing it out. I ordered one to see how big it is, and whether it can be used or modified for use in the printed U-Boat. Then I discovered a micro water pump specifically designed for ballast tanks. You can see it here: http://www.rc-sub-workshop.com/Details.aspx?id=195 http://youtu.be/ux5lRQt77wU This pump works with both water and air. I don't know if they are bi-directional, but I ordered two of them. Ideally I can run the pump one direction to flood, stop the pump, then reverse direction to blow. Even if they only work one direction, I can do some clever porting with SMAVs to flood or blow tanks. If I get creative, I may even be able to run both a main ballast tank and a trim tank.
RE: 3dp u-boat update: the pump has arrived. It is small enough to fit inside the 3d printed Type VII, and able to fill up my small syringe in just a few seconds. Unfortunately, it is non-reversible. After a brief study of the MAG throttle, I was able to adapt the design to moving water using SMAVs instead of wires and micro-switches. All I need to do is add an electrical switch to start the pump whenever one of the SMAVs is pressed. The pump runs fine on either 7.2v NiMH or 7.4v LiPo. In the interest of comparing with other submarines of the era, I drew up a quick spreadsheet to calculate the amount of ballast a scale model would require to go from scale waterline to fully submerged. Basically I took the difference between surfaced and submerged displacement, converted to volume based on seawater density, then reduced to 1:144 scale. type VII: 2.085cu.in or 1.2oz Type IX: 2.450cu.in or 1.4oz Type XXI: 4.651cu.in or 2.7oz Gato: 18.668cu.in or 10.7oz Surcouf: 21.887cu.in or 12.65oz Argonaut: 23.153cu.in or 13.4oz I-402: 27.763cu.in or 16oz This can be used to estimate the minimum volume needed for a ballast tank to take the ship from scale waterline to submergence. I recommend a little extra volume to compensate for construction errors, size, etc. Better to have an over-sized ballast tank than an under-sized one.
RE: 3dp u-boat Inches? Really, Carl, it's so very droll of you to use antiquated units of measure . Do use drams next time
RE: 3dp u-boat "Based on seawater density??? Given that seawater is more bouyant than fresh, and we battle exclusively in fresh... Betcha your sub sinks like a rock & stays there if you use those numbers. Reminds me of the time I went Scuba diving in a spring & forgot to change my weightbelt from the "diving the Keys" amount. Stepped off boat and 3 seconds later was standing on bottom in 60+ feet of water. I think a better way of calculating would be to float your model in a sink or tub, noting displacement. Then sink model and note difference. Calculate off that empirical data.
RE: 3dp u-boat The nice thing about most R/C ballast tanks (both piston-type and pump-driven) is that you don't have to fill them up all the way. Just take on water until the ship goes under, then trim for neutral. I've even seen specialized depth controllers that read desired depth from a servo signal and actual depth from a pressure sensor, and blows/floods ballast as needed. Besides, I don't actually have a hull for most of these boats that I can test. The spreadsheet is the next-best thing.
RE: 3dp u-boat I'll disagree slightly. It's OK to fill a piston or bladder tank partially, but not an open ballast tank. You don't want to have a free water surface inside the tank which can shift your trim as it sloshes back and forth. Actually, even a bladder tank might have that problem, it depends on how it is constrained.
RE: 3dp u-boat I'm thinking of something more like a syringe. Piston pulls back to draw water into tank (no free water surface). Piston drives forward to expel water. For purposes of trim it would have to be dead center in the boat.
RE: 3dp u-boat Except that as you pull the plunger back, it changes the trim of the boat as the water volume expands...
RE: 3dp u-boat If you look at the professional piston systems, they use a piston at each end and move them at the same time. That way the ballast fills to both sides of the center of buoyancy and keeps you balanced.
RE: 3dp u-boat A few years ago I attended a SubRegatta in San Francisco. I saw a lot of different depth control systems there, ranging from true scale (air-blown ballast tanks for buoyancy, fairwater planes for depth, stern planes for level), to semi-scale (two ballast tanks, one ballast tank and planes, planes only), to non-scale (pull-down motors, rotating motor pods). Even among ballast tanks, there were many variations. While many of the true scale boats used solid ballast tanks and valves to ingest/expel water, most semi-scale and non-historical boats used pistons or bladders. For the piston ballast tanks, the ideal is as RCENGR described: two ballast tanks, moving separately at both ends to control both buoyancy and trim. But what I more commonly saw was a single ballast tank, carefully positioned at or just forward of the CG. As long as the boat's CG was forward of its center of lateral resistance, the forward motion of the boat would tend to provide a levelling force, much like the fletching on an arrow. They also usually had dive planes to control trim, but this method worked quite well, even with piston-type and bladder-type tanks. A few weeks ago I ordered a small toy submarine with ballast tank depth control, to strip for parts and see if it could be used in the U-boat. Unfortunately the darn thing is way too much fun, I can't bring myself to destroy it. So I ordered two more The important thing, though, is that it clearly demonstrates what I described earlier. This boat uses a single ballast tank, barely forward of the CG, for buoyancy control. Trim until you are negatively buoyant, dive to the desired depth, then trim neutral. It points slightly down when fully negative, and slightly up when fully positive. At neutral, it sits about level, and moving forward also makes it level. I usually sail it at night, when the water is calm and I can better see its running lights. A single green LED in the top shines a beam of light upward, with several smaller beams radiating forward, to either side, and aft. At shallow depths, I can quite accurately judge depth based on the upward beam and its reflection off the surface; at greater depths, the upward beam fades and the sideways beams become more prominent. There is a single dim red LED in the bow, which I hope to eventually replace with something much brighter. Alas, photos do not do this majestic creation justice. There is actually enough light to see the hull and some of the surrounding rocks, but my poor phone camera cannot handle the low-light conditions. with flash on, the camera can see the surroundings, but not the lights... and with flash off, it can see the lights but not the rest of it...
