Well after several years of battling I've decided to do a refit to my first sanctioned build, HMS Invincible. She has performed admirably but after gaining more battling experience I've become more "aware" of certain areas that could use some improvement. Here is the original thread I had created for her: https://rcwarshipcombat.com/threads/a-tale-of-success.445615/ Things that I want to focus on for this refit: -She turns OK, but could be better given a dual rudder/4 prop ship. I plan to re-do the drive shaft and rudder placement for improved turning. -Pump output has been slightly lacking, especially after moderate damage. Speed has also dwindled later in the sorties now that I stay out there longer and take my time lining up shots. So my plan is to go from the 6v 12ah SLA to 2S lipo. This should give me more consistent drive power and a bump in pump RPM. -Several places on the deck that were sealed with original bondo brand resin are showing what I think is UV damage. Time to do some sanding and apply some West System. Also the aft deck insert could use a deck seal since its the lowest weather deck. -Add a little extra water channeling to the extreme bow and stern I contemplated switching over to solenoids but decided against it as the servo/poppits have been working well enough and I don't really want to spend the extra money. So to improve turning: Initially when I got the kit from Strike the drive shafts that came with it were too short but I made them work anyway. The result being the propellers a little too far away from the rudders and the rudders being a little bit forward of where they probably should be. By moving the rudders aft a little bit I should be able to increase the moment arm of the prop wash from the CG. But of course most importantly I'll get the props nice and close to the rudders. I got the old shafts ripped out. Ordered new shafts from servocity, bushings from Mcmaster and stuffing tube material from the local Hobby Town (pre-Corona). I also removed the old rudder setup and drilled new holes further aft. This also helped because the bottom of the hull is flatter here which allows me to get the rudders snugged up against the hull better. I 3DP new rudders that I thought would work better than the stock cast resin ones. I also 3DP a drive shaft jig to get everything spaced nicely. Hot glued it in place while the epoxy resin dried. And final product: That's it for now. I need to reinstall the rudder servo assembly now that the rudder posts moved aft.
A little progress. The drive train is pretty much re-installed along with the rudder servo mount. Put in new nylon drive gears for the hell of it, old ones looked fine. Otherwise I've repaired any UV damage with a new coat of West Systems and I got the lower step deck seal improved with a layer of silicone. I've also added a little extra water channeling to the bow in the form of Smooth On Free Form Air. At this point I'm waiting to pull the trigger on a set of new batteries and charger. Then it should just be a matter of re-ballasting and then testing everything.
I'm considering a refit on my old Invincible as well. I intend to move my rudders FORWARD though. The rudder is a lever, centered on the rudder posts. The farther forward they are, the more leverage you should have. I originally had 6v direct drive in it, I plan to bump to 11.1 lipos, using a gear drive. I want to get rid of my mickey mouse ear props, and use home-made props instead. The tips of the props are the parts that move the fastest; I want the blades to be as fat as possible. Those changes should improve acceleration, deceleration and turning. I'm also considering trying to reverse my motors so they sit over the dog bones in space that's otherwise not used. I need to check the fitment though to see if that's going to wok for me like I want. For my guns, I presently have a sidemount in X turret, a stern gun in Q turret and a sidemount in A turret. I plan to change the q turret to a sidemount to give me a quasi-death Y, and move the stern gun to P turret which isn't very far forward. I doubt it will lose much effectiveness. I also want to move the CG aft, my bottle is presently in the bow. I want to move that weight aft, so it's closer to the rudder, which should help turning by reducing the work my lever (the rudder) is trying to do. the radio will be re-located to the bow.
I'm not sure I follow your logic on moving the rudders forward. My line of thinking was equivalent to the forces on a see-saw. The CG of the boat was the center of a see-saw and the kid on the end was the rudder. A kid at the very end of his side would over power a kid of the same weight closer to the center. My primary goal of course was to get the props closer to the rudder. I dont know how much of a difference moving the rudders an inch will be.
It moves the pivot point forward so there is less leverage against the rudder. Your analogy is slightly backwards. You're trying to move the kid on the end, not the one in the middle By moving the rudder father to the end, you're making it do more work to move the boat. Try this if you can. Take a baseball bat, hold it at the end of the knob. use your wrist to swing it around some. Now, move your hand to the top of the tape. the bat should be pulling on your wrist less. Swing it around a bit. it should be easier to swing, because your CG is closer to the pilot point....the wrist has to do less work.
You've given me something to think about though, I need to think more on the relation of the rudder to the GC and not so much to the bow of the ship.
The other analogy I would use, and this is a good discussion we're having here, is that of a big wrench vs. a little wrench on a lug nut. We know the bigger wrench will apply more force to the lug nut given the same applied force at the end of the wrench. In the case of a boat, the lug nut is the C.G. (which typically cant move in our models as the internal weight is fixed). When the water is deflected off our rudders that equates to our hand pushing on the end of a wrench. Given the same amount of deflected water from the rudders, if that force is further from the CG a greater turning moment will be applied to the CG and thus I would assume the boat would more quickly rotate along its axis centered on the C.G. Thoughts?
I found a document online that helped me considerably. You are correct. I was thinking of the rudder as the lever and pivot point, and that was incorrect. What I need to do is move the pivot point (which is not the rudder) and that is done by the longest length from the center of gravity. The applicable text from the doc I found was: Firstly, the minus (‐) sign indicates that the pivot point appears on the other side of G from Fc. Secondly, a bigger GFc yields a smaller absolute GP, which means that an external force farther away from G causes the pivot point to be closer to G. These two findings are essential knowledge for the practitioners to proactively control the pivot point. That's what I want to do, is move the pivot point closer to the center of gravity.
Small update, worked on some flags. For those interested in making your own flag this is what I do: -Find the appropriate flag on the interwebs and open the image in paint or similar program. -Print the flag on a regular piece of paper to see how the size came out and to know what side of the page the printer prints on. -Make adjustments to the size of the flag in paint or with your printer properties as appropriate. -Tape some silkspan onto the piece of paper where the flag will print trying to keep the tape nice and flush so it doesn't rip or jam in the printer. -Print the flag, remove from the plain paper and cut off the extra silkspan. I leave a sliver along the edge of the flag to glue onto a piece of string. -I cut a long piece of string and try and make it taught between two objects. -Using a toothpick I apply some CA glue to the point on the string I want to attach the flag. -Once the CA glue has dried keeping it on the string I coat the rest of the flag with CA glue to waterproof it. Once the CA glue dries the silkspan becomes mostly transparent so the image will show on both sides. I've noticed the CA glue sometimes curls part of the flag which actually adds a quality similar to the flag billowing in the wind. I'm adding this small flag (burgee) to all the ships in my fleet. It's the flag that represents my father's actual boat club (full size seen in background).
Another small update. Motivation has been low since every SCRAP battle since April has been cancelled due to Covid-19. Everything drivetrain-related is pretty much re-assembled. At this point I just need to order the new lipo batteries and then 3D printing a battery hold down of some sort. Here is the steering gear re-installed. Also added was some light-weight epoxy putty to help keep water sloshing into the extreme stern. Although hard to see, silicone was added to the step deck seal to help keep enemy prop wash and stern diving water out.
consider using servo city plastic chain and cogs/sprockets for the rudder linkage. very strong and can adjust throw with differential sizing. It will avoid locker that can happen with rods.
It is handy but you don’t get differential steering. Meaning the inside (of the turn) rudder has more deflection than outside rudder. If you size the arms appropriately you should never lock up the rods.
I'd fill in that space between the shafts and make a hard 'step' there to help even more with keeping water in the pump sump when you're driving around.
That is a form of doing it but that’s not actual differential steering it’s more just steering bias in my estimation.
I hadn't thought of that. I believe it is called the Ackerman effect when used in car steering. now that you mention it, that was an important part of tuning a car when I raced RC - a lifetime ago.
Now that I have had a chance to think about this: Ackerman effect is necessary when the wheels are firmly planted . With boats, the rudders glide in the water and have some slip. Also, from an article I read some time ago; the physics/theory is that - in ships, turning is caused by hydrodynamic flow over the rudder AND, partially the jet effect of the water directed off the props by the rudder. In full size ships, this is 80% hydrodynamics and 20% jet effect. At hobby scale, forces change and the importance is reversed. 80 jet, 20 cutting through the water. Conclusion: differential angulation of dual rudders matters not so much.
Toeing your rudders in or out does help with turning but not because of what you’d think. When the rudders are not straight they cause extra drag and slow the ship down. To make speed you add thrust. The added thrust is what makes the ship turn better.
