I'm building a small ship (10" tug) to get accustomed to shipbuilding techniques before I build a Big Gun ship -- I want to make my mistakes more quickly on a smaller scale. (I realise that smaller sizes are in some respects more difficult than larger ones!) I've successfully built a hull (http://www.rcgroups.com/forums/showthread.php?t=1616651), now it's time to mount the machinery. I'm using a converted servo as power, which is obviously not the same technology as a larger ship would use (I may use a small brushless instead), but I'd like to build the stuffing tube to the same design as a larger warship, if possible. I'm planning on using 3mm brass rod, running inside a 5.64mm inner diameter brass tube, with plastic bushes of 3.175mm inner diameter at each end (http://www.hobbyparts.com.au/store/...beflanged/) I'm expecting to need to use some glue or crimping to secure the bushes. I probably won't bother attaching a grease injection port to the tube. I'll let the propeller/bush surface be the thrust bearing. Is this a viable design? Would it suit a large warship? Thanks for any comments/suggestions. Tom
Build suggestions? I'd avoid the brass rod, in a short tube there's a tendancy for it to wear quickly and leak. I use 3.2mm stainless rod for my shafts, with a brass bush on the motor end and oil-impregnated nylon (Oilon) for the prop end. Bushes are drilled to suit the shaft and then polished for a tiny clearance. A small copper washer used as a spacer acts as a flinger to help keep water out of the tube. The shaft is actually a cut down stainless welding rod. I'm a boilermaker so it's easy for me to obtain them. Motor was removed from a cheapo animated xmas toy that blew it's circuitry, type unknown, but it's pretty efficient. ESC is a LRP runner reverse, power comes from a 3600 mah transmitter pack. Pump was built from a constant speed brushless motor from an old 3.5" disk drive, a short section of 1/2" conduit and some bits and bobs. One mini servo for the rudder, set to use it's whole throw to minimse load on it and presto! I have probably the most manueverable and annoying ship in the AusBG!
Ahoy there Tom, In my tiny transport (about 14" long, 2" beam), I used a short length of brass tube for stuffing tube and a 1/8" brass rod for propshaft. It was crudely assembled because the person before me buggered it up, but the setup worked just fine. As long as you have enough sealing surface there and some grease, you shouldn't have any issues. What you described would also work, if you use glue. Just be sure your bushes are properly aligned before you glue them down. If they're slightly crooked, or the tube is slightly bent, you'll get a lot of resistance and that hurts the performance of small high-speed motors like servo motors. I found that a servo motor and 4.8v receiver pack was not sufficient to get my ship up to the 25 knots it's allowed under WWCC rules. I had to use a slightly larger motor from a surplus store, and a 6v receiver pack. Once I made that hardware change, the ship was almost untouchable; it could turn circles in a toilet-bowl, and out-accelerated every other ship on the pond. For ESC, I used the micro Mtroniks 10-amp ESC sold by Strike Models. Good luck with your build!
As it happens, smallparts.com.au were out of stock of the bushes, so I ordered some Graupner propshafts from Corwall Model Boats instead -- that will work out cheaper, but won't allow me to adjust the length, and won't leave anything over for future builds. (At least, they don't recommend moving the bushes within the tubes -- I'm not sure if it's possible). @Darren is your copper washer attached to the shaft? @Kotori87 we'll see how the servo goes -- I'll be running it at 6.6V (2S LiFe -- when hobby king actually gets stock and delivers my order) so that should give a bit more power, and this is a smaller boat, so maybe it will be OK.
