4BDN Jetboat hull

Last crawled date: 4 years, 2 months ago

This is my latest stepped hull, a work in progress. Lots of advantages come with the steps and specific tile orientations to affect boat handling behavior.
I'll be CNC routing a model and creating a mould from the model.
Stay tuned for updates.
14/1/2020 Printability!
I hate models that require use of support structures to print. However, after my updates I posted below I realised that the saved split finalised model wasn't from the latest render. Retracing my steps, I found that the render failed at a particular point, I suspect after I'd saved an stl in a different format program than openscad. doesn't seem to be any way around it. So I've printed a stern piece with some manual assistance near the holes above the jet unit. It's not great in that region but it's quite usable. Next time I'll add supports.
The Bow: I had planned to print it stern end up, bow pointing towards the heated bed. This looks great with support added up to 250 layers, I'm using 0.3mm per layer. So the whole thing appears quit printable, although a bit heavy in filament. I still have about 2.5 days of printing to complete it. I'll be sealing each section before assembly, still not sute if I'm going to use bitumen tape from my resin infusion supplies or glue or blue-tac
The 6 mini servo holes have a cable duct underneath and are general purpose except the two centre ones are reserved for steering and the option of a vertically trimmable steering nozzle mod. Plan is to fit the servos in with bluetack or power tack sealing all around the servo and cables in the servo mounting hole. Shouldn't be any need for screws, the steering load on my nozzle design is very minimal. Bottom two holes above the stator attaching point are for control rod boots. If you only use one then fill the other. Top two holes are for cooling water in from the stator and warmed water out from the ESC and motor. Don't lengthen the battery side motors or you will be wearing a sad face when the ESC caps blow.
12/1/2020. Been printing the stern. Found a region that didn't show in the 3D renders that prints so thin as to effectively be holes, either side of intake. Patched. Didn't like the chances of a nice print inside the transom where the coolant tubes and control rod boots attach so I went back in my openscad programs and thickened, added a mid bridging support flange and just covered the holes on the inside of the transom so the bridging won't be interrupted. Did a quick check of a 5mm shaft in the intake bearing housing, found my 5.4mm oversized hole slightly touches, be sure to add a bit of grease so the PLA doesn't turn into a hot-mess.
Added bottom support for the motor flange as this is the region that will take the most stress. Corrected the motor fixing hole spacing from 15mm between centres to 25mm between centres. Thinned the shroud that acts as a spray reducer.
re-rendered each step and made a fresh 3-segment model which can be split in a slicer.
Note that the bow section is printed stern end down, may need to watch layer height as it builds outward quite fast but should be achievable.
Also note that many popular slicers falsify the popup notes for computed nozzle width vs actual, the % setting bases not on actual nozzle width, but on layer height. Causing a lot of people to get non waterproof prints!
Later on 11/1/2019. Fitted the motor flange, the bearing holder and a trial water deflector.
Subtracted 2 x 0.01mm thick planes to section it into 3 pieces. Now it should be printable.
There is a cone between the jet unit shaft stub and the motor flange that is to make the printing nice, it should be cut off after so a universal joint can be fitted. No kiteboarding today :( was too wrapped up I finishing this!
Created 0.01mm shear planes, divided boat into 3 sections. Loaded to slicer, separated the 3 sections, oriented each for printing and saved them. Added here, also with one of my stators(what restarted all this designing) and 4 steering nozzles. Bearings need to be 13mm OD, 5mm shaft, ceramic. There is a 10mm tube stub front of the intake bearing collar for a grease seal.
11/1/2019: Tried fitting a free stator design(FJD) but neither freecad or opencad were allowing the union operation. So I knocked up an intake tube of my own and fitted it, no dramas.
Now I've got to create and fit the shaft tube with bearing holes and the motor mount.
8/1/2020: Created voids for up to 5 x hobbyking Rhino 5 amp hour 50C 3S LiPo batteries, a 150 amp water cooled ESC, up to 4 mini servos, an FJD intake and a grunty 1700kv motor.
Also created internal holes and nut fitment pockets for SS Threaded rod fitting to tension 3D printed parts for additional support, now looking seriously at 3D printing this in parts. I've also constrained the outer dimensions of the hull: "resize([280,650,100])" which will let me print it in segments diagonally in my FLSUN cube printer.
17/12/2019: Switched out original hull with "fluidity 4BDN Hull.scad" with slightly changed stator cavity and with an intake pad to simplify jet unit mounting. There is a 3 degree downward tilt for both intake and stator.
I'll also be updating here:https://www.rcgroups.com/forums/showthread.php?3483031-4BDN-hull
And there are some stators I've designed here:https://www.rcgroups.com/forums/showthread.php?3441451-4BDN-FJD-35mm-stator-alternative
(These fit to the FJD inlet and impellors on the same forum.)