The picture above is the 4 bar linkage solution. the 1 unit length is the center to center spacing on the axes, the 2.4 unit length is the length from each axis to it's linkage's tieoff point. This type of linkage (and the crossed variant of it) both require a hugyly long and unmanagable servo arm/rudder horn arm to get the motion that I want. Both also have the problem that they "cam over" at the top, which is really not a good idea unless you are making a pair of vice grips or similar structure. in this hull's case, that would require a ~7.5 inch radius on the servo horn and rudder horn.
Hmm ... after rereading the rudder movements you are trying to get, now I understand why my idea won't work. The differential movement combined with the 90 degree requirement for the side rudders really makes it tough. The only mechanical way I've come up with involves 6 gears and two linkage rods. The gears are for multiplying the servo travel to each rudder individually, and the rods (and rod end placement) positioned to get a mechanical differential to reduce rudder throw in one direction independently in each side rudder. I'll see if I can sketch it up over lunch, scan it, and upload it here. It might be easier to use three servos and transmitter programming. Heh.
yep. I am thinking I may just give up on it and go +/- 45 on the secondary rudders.... need to do some math on the impact of that. simple with chain drive (little tight at the stern to get full size servo + gears)
That would make it much much easier. You could still get a differential movement using linkages ... it won't be as much as 90 degrees though. Perhaps 55 - 60 with a normal servo and playing with the rod angles and connection points.
Can you handicap a little and toe the outer rudders out about 20 degrees or so for their neutral position? You'd get most of the swing outwards that you want at the cost of the rudder throw towards the hull. Not sure if BigGun rules would prohibit that though or if it would get you close enough to what you want to be worthwhile vs just going +/- 45.
Greg I received my new book called Italian Battleships of World War II author Mark Stille in paperback form. Illustrated by Paul Wright. It's a great book on the Italian Fleet with beautiful art work and photos of the Veneto Class and other battleships in the Italian Navy. The varioius paint schemes and a centerfold of a cutaway of the Veneto. Great little reference book. Curt
Preliminary rib layouts are shown below. I plan to fill the open areas in the hull with balsa for regions of high curvature and with 1/32" ply in lower curvature regions. once filled, I plan to put several layers of fiberglass on the outside of the hull below the penetrable region. I decided to try a little experiment where I recesss the 1/8" balsa into the hull so that the line is not so noticable. I may or may not do that in the end, but so far it looks feasible (although it adds to the carving). the multiple horizontal stringers below the required penetrable area are there to support that design feature. The aft end solid area rises with the 45 degree down angle on the hull the rib layoutis still rough, and things will change/be tweaked. I'd like comments.
The rib layout looks pretty good as is. I think I would put a little more of a radius on the subdeck interior corners to make sure there is good torsional rigidity, but the ribs look good. I'm not sure I understand how you are doing the 45 degree sheeting in the stern. Is what looks like multiple stringers there to support the balsa you plan to sheet with, or do the multiple stringers actually make up the hard area? Or something else? Mark
a bit of both. The balsa is inset for it's thickness, so the multiple horizontal parts rise with the rise in hard area provide both that inset and a hard boundary below the balsa glue joint. and I figured that it isn't that much area, so I would just extend the lowest one all the way to the stern and work up from there. I will probably radius the deck more, there won't really be a sub-deck per say, just a section of not yet drawn wood to form the bottom where the removable deck will sit.
Well, I decided to do away with the rudder requirements I was going for in the previous post. just didn't make sense to put all that effort, money, and time into a system with such a low added benefit (now that I have figured out several ways to achieve said motion, none of them cost/reliability ok, however). So what I went with was a chain drive (never done one of them but with the servocity parts, it makes it easy) and with mcmaster carr selling stainless steel chain, that takes care of the other concern. What is drawn below is a single standard sized traxxas waterproof servo driving all three rudders with the primary getting +/-90 degrees and the secondaries at +/-45 degrees as drawn. increasing the driving sprocket size will symmetrically increase the throw on the secondaries, up to +/- 90. There is enough adjustment to tension both chains properly (although I will probably add more where space allows). All fasteners are bolting into metal inserts intended for wood, so that I can seal that wood assembly well. I am still debating about the removability of that whole assembly. I may go as far as to have a permanently mounted stuffing tube with a smaller, bearing containing tube, inside, such that the whole rudder assembly can be proven out and maintained outside of the hull of the ship. we shal see if that is worth the trouble, as I suspect that it is not. The latter pictures show how other components fit, including some gargantuan arizona style cannons. If I ever get my mill back up and runninng (or find someone who will let me use their's) I will get back to porting my cannons over to 1/4" from 3/16" but anyways, still tons of work left before even a single part can be cut. Prior to rib detailing and layout for cutting, the drive motor/gearbox needs to be designed. The pump needs to be located and mounted, and provisions for main turret rotation need to be added. Superstructure will come last, no matter how nice she looks...
I completly forgot about the Gears and chains from Servo City. If I decide to convert Roma to full operational rudders than that would be the type of system I would use. Looks good Greg.
Well, it has been a while, but hull draing work is progressing (in 15 minute increments) I figured out a better way than before for the bottom of the hull and the stringer using 1/8" square and 1/8" X 1/4" basswood strips. see below. now I just need to tweak the cutouts in the ribs slightly so the basswood is bent about it's centroid for the twist and then only bent in one more direction (slightly) rather than the two shown in the model. that should reduce the trouble (that and installing after steaming as necessary with clamps, letting dry, checking, and reinstalling). There will still be a laser cut "keel" on either side of the ship in the impenetrable region to help with rib spacing uniformity. it is not yet drawn, and will be one of the last major components. The motors, mounts and shafts are basically designed in (see last picture) as are batteries (~10V, 20AH) and the CO2 tanks (a pair of either steel 9oz (my preferred tank as it is only 2"OD) or a pair of 2.25in OD aluminum 9oz or 10oz tanks with strike regulators. the model is the old regulator, but there is ample space for the new one, whenever it is finalized and can be drawn in. large strike model's pump has been designed in as well. As with my last ship, shafts will be removable via the clamping shaft collars. It is interesting to design in wood. there is a lot of flexibility but also a lot of differences than how I would go about certain features if I could add 3d features. I checked into 3d printing some of the superstructure, but it is prohibitively expensive (the 90mm AA turrets would be ~300$ each. now I would only need one to pull a mold off of but still). Anyways, onward and upward. I plan to try to get it to the point of cutting a hull sometime mid may, with the superstructure being a next winter project after cannons are finalized and installed. (unless someone wants to volunteer some rapid prototyping/machining help, then I could be convinced to pull some superstructure parts molds sooner)
Very nice work. I know it can be time consuming to plan the layout and check it with the 3D drawing, but I think it is time well spent. You end up with a much neater layout and don't have to kluge together supports because there is too much room or make cuts because there is less room than you thought. And when you design in things like the servo and motors mounts, it really goes together fast once you have the parts on hand.
I can't wait till your model is operating with the 3 rudders and get feedback on how well the model turns with the 3 rudders.
Well, considering this is a big gun ship, and the props are at their scale locations, I expect it to turn poorly compared to any fast gun variant. If I configure it for fast gun at some time in the future, the inner shafts will be lengthened, the outers will be turned into drag shafts and the bulk of the rudder area will be put on the back rudder (easy to do, as the shafts are all removable with an allen wrench and the rudders can be easily removed as well) Part of the difficulty of the design task has been to design in the flexibility to go from a well setup big gun ship to a well setup fast gun ship with no permanent changes... (when I get to cannon mounts, the cannon subassembly will be readily removable as a unit(s) to enable a quick swap)
Wow. A month gone by and not much to show for it (that is readily visible) the picture shows the underside of the hull... shaft supports are in, the port and starboard gas lines have been located. the pump location is set and the tube geometry for the pump outlet is set. Most of the month was spent on rib detailing and trying to figure out a cannon design I can fabricate with the tools at hand... (mill in storage for another year or so at this rate). It is interesting when one is limited to 2D parts, the challenge is good. as an aside, a combination of precision ground rod and long bushing (yes, they are available) should work well for cannon depression, even if made with a dremel... Now if I can jsut figure out the rest of that, it would make the hull layout easier than the large space claims that have been left for undetermiend cannons.
Wow that is so impressive. I am learning a lot just by the visual layout this way. I look forward to refitting Roma with a 3 rudder system.
Well, after another month of an average of 5 minutes a day to work on the design, the parts below the waterline are almost completely designed. A few details left on the aft section of the keel and the rudders themselves and the waterline down will be completely designed. The parts are self aligning (and perhaps a bit overkill) but we will see. There is a central water channel that also provides a mount point for the batteries I still need to add tieoffs on the side to clamp the batteries firmly in place but that is straight forwards. Next up is to design the horizontal stringer into the ribs and then finalize the deck to rib interfaces. After that, deck tiedowns, and then a final check, and a first hull can be cut, sans superstructure. Current weight rollup estimate is about 30 pounds with the plywood modeled conservatively dense to approximate sealants and other non-modeled wood. Superstructure which is not designed accounts for 6 pounds of that, which is unrealistically heavy, but that will give me the extra weight to cover a pound or two of electronics that are not modeled. Slowly she gets further along... The biggest glaring deficiency is the cannon situation (I.E. they are big gun traditional cannons right now, but we will see what actually goes in there) there is one of my 3/16" twins modeled in as well, overlayed on the aft turret (hence the wierdness protruding from the aft most turret.
