DRAGONFIRE81M

heres some pics of the molding of the stater nozzle i also molded the sharpend stater in so no glueing . the last two pics are of the cracking impeller housing

grael

If you just want to fix it, then wrap some glass fibre cloth tightly around it, thenthread around that, then squirt CA glue over it, and leave it somewhere ventilated for an hour. Thne, re drill, sand and it should be ready to use again.

damfurst

Just a few more pics of abc hobby jet. Also, a picture of servo, mechanical speed control, battery tray, & receiver battery taken out of ski jet. All that replaced with 50A esc and velcro for battery on bottom.


Wanted to let you all know that this jet ski also has reversing capability with this set up like headhunters latest too. There is no reversing bucket, just reverse on the esc. Pretty sweet. It wouldn't reverse with the mechanical speed control even though it had it.

Quicksilver

I'm so excited, I've decided I'm going to build a boat out of wood, but I'm designing it myself. I just got the latest version of AutoCAD and after 6hrs of practicing, I somehow remember everything(it's been 10yrs).

I'm going for around 20"L x 7-8"W I think I'm going to jam the 28mm in there with the 700sc or twin mini's. Either way it's got to be small, cheap, fast and reliable.

DRAGONFIRE81M

TWIN MINI !!! i have molds made for the inlet cover ,stater and nozzle. from a nock off jet drive .

grael

Hi quicksilver,
I've never used Autocad, but I have within the last week downloaded Art Of Illusion which is free, open source, and has the power to animate, show textures, solid materials and draw in various ways. It's quite a bit to get my head around, but looking very worthwhile. The reprap project are also using it as their software for creating parts to print in 3-D, which was my inspiration.

You can create basic surfaces, donuts, spheres, cylinders or polygons with n sides, taper etc, and then tubify, lathe, warp them with a big variety of tools. If you want to paint your boat with wood, plant textures, or even glowing paint, it's all possible.
http://www.artofillusion.org

graham.

grael

Have a project at the moment to set my woman's son up with a RC jet boat.

We're using a little .12 (2cc) water cooled ASP, and the impellor diameter will only be 21mm.

I've built the intake and hull (hull is a lightweight version of my blue one carying my .40 ASP), but I will be keeping the weight right down on this one. So far, it's about 730 grams, but there is engine mounting, outlet, fuel, top and RC gear to go. I'm hoping to get it running at around 1300 grams or less. With the small engine, run times should be over 30 minutes on full throttle.

I moulded my intake out of electrical conduit and PVC plastic, then moulded around in silicone, then filled the silicone with polyurethane plastic.

Outlet/stator next !

grael

This is the outlet-stator, I've modeled it out of PVC pipe, sheet and polyurethane fill for the inner taper and outer ring. I will pour silicone around it, and then do as many copies as I need in polyurethane plastic. The original has low strength, but each urethane pour will create fibres alligned with the flow as it enters the mould, and the hub will become a part of the outlet via the supporting flow correction vanes. It's fiddly work building something so small, but the materials costs are less.

DRAGONFIRE81M

looks nice man cant wait to see this one running . but im not sure how the .12 will do . i was thanking of a .18 for a 19mm drive

grael

Hi Dragonfire,
it depends on the nozzle restriction and the impellor pitch. I'm going to try with a cut down stock prop for the .12, which has hardly any pitch on it, but I've restricted the nozzle a lot on this one, and so I think the engine will be slightly over powered by the time you factor in amount of trimming of the prop to make it into an impellor. If it doesn't work well, then I'll take a stock 35mm prop and cut that down, but then I'll need to open the outlet right out, give it the same cross sectional area as at the impellor, but minus the hub. The stator vanes let me use extremely hig pitches.. but I haven't ever done a jet unit this small before, so it's going to be interesting to see the result. The small impellor I'm going to use doesn't have a lot of blade area.

Or maybe a custom impellor ?
I don't really want to use polyurethane for an impellor though, I think they would break too easily unless made quite thick.

Graham.

grael

I missed the details of your top post on this page ! you're moulding in the stator too ! Good work...

If you want to modify, or do your own, then I'm finding the fastest way to prototype is with electrical plastic conduit for the tubing. you can take slices out of one side and then bend it, or do it properly with a bending spring. Then, you can glue PVC that they stock in hobby shops, (in all different thicknesses and extrusion profiles) to quickly make up a model. Then, mould and convert to one piece plastic.

I would switch from epoxy or polyester if that's what you're using though, if you pour in two part polyurethane, then it will go off quickly with very little heat, and be a little more forgiving of shock loading.

DRAGONFIRE81M

yeah the stock grupner has a glued in stater . but i have had problems with it comeing unglued and frictun welding to the prop . i for got your makeing your own stater and useing diff pitchs so you can run a higher rpm . as for the mini jet from grumpner i would use a .18 with around 1.3 hp

its a urethane that im useing to cast. im useing alumlite molding and casting system you can get it from hobby lobby " the crafts store " not the rc

http://alumilite.com/ProdDetail.cfm?...milite%20White

grael

I'm mostly using the "easycast" urethane product below. Slightly less work time, and slightly more flexible.
If you have any cracking problems, then try a lower shore hardness, yours is 72, my one is 65D, and I've had great results.

If you are moulding again, I suggest you add in some personal features before taking your mould, water outlets, scoop pivot points, ride plate attachment etc, that way, you shouldn't run into any copyright issues with the original manufacturer. You can make inside carvings of features in wax, then fill with urethane, that's how I'm making hubs.
It's Christmas day here, but in between things, I'm dipping my stator outlet in PVA mould release, the surface tension while drying smooths off irregularities, and fillets out sharp inside corners so that my final pieces will be better quality and stronger.
http://www.topmark.co.nz/articlelive...Full-View.html

DRAGONFIRE81M

yeah i added some changes with that in mind i fixed the cracking area in the weck mounting flange made it solid in stead of resases . also sharpend and made the stater one piease .

grael

My latest mould:
The first, showing a moulded outlet-stator before trimming, and it's mould.
The second, my fast (around 50Km/Hr) boat with a .40 asp on the left, on the right is my woman's son's boat I'm making him.
The third shot, inside the boat you can see my exhaust arrangement, the tube from the muffler to the stern would never last without cooling, so I've taken the water from the engine water cooling outlet, and directed it inside the exhaust outer chamber via silicone tubing and a brass pipe.
In the fourth shot, you can see the final exhaust outlet, I've silver soldered brass strip to the end of SS tube at an angle, and drilled small holes. it will exhaust down like an outboard, and run quietly !

damfurst

Hey Grael, that looks so cool. I wondered what kind of pitch do you put on the stator vanes when you make them? I've wondered about playing with ones that I have to see what would happen but haven't quite figured out how much to change them.

It finally warmed up to 35F yesterday after 10 days of below 0 and stormy weather. So I had tried what you said with knock off boat and changed my motor from titan 12T to a titan 23T 550 size motor. It still wasn't running right. Lots of cavitation. Was going to pull out of the water and do some adjusting on the impeller but before I could the ujoint came apart. I didn't expect that. Down the creek it went though I was able to retrieve it. Thought I'd show u a picture of that mangled mess.

grael

Hi damfurst,

Last two stator-outlets I've made, I haven't put any pitch on them. I have, however made them in a sort of hydrofoil shape though, like a solid wing cross section, but sharp at the front. So on the side the water spins against, it is flat, the other side the water curves and then goes straight.

My impellor this time is a cut down 35mm prop, not sure how it will go, as I have quite a bit of nozzle closure, I may have to trim some length to get the flow volume up, or failing that, make a custom impellor. being cut down, it's pretty high pitch.

I had real success with my second to last jet, but my big test of the new one is very soon, this morning. Don't want to wake the neighbours before 9am, even though I have quite a lot of muffling on this one.

Graham

grael

Here's the bare boat tunning in my tank, still needs RC and a top:
http://www.rcuvideos.com/video/1000054-mov

DRAGONFIRE81M

ALSOME !!! it does sound like it could use some more pitch .

grael

Hi Dragonfire,
It's got lots of pitch already !
It doesn't self prime very well, but I'm thinking with the pitch it does have, it should load up more with speed. we will find out in due course... The engine doesn't speed up a lot when I take it out of the water, maybe 30% ? I'm happy with that. We will probably be running on mostly 10% nitro. I think the thrust is around 600 grams, haven't taken a proper measurement yet.

jetboata

hi guys

im sort of a newbie to rc boats so any help would be appreciated.

was just wondering, those of you who are using the graupner mini jet or similar units how have you attatched the stator to the hull, eg: with the 4 self tapping screws it got supplied with or glue, etc. i was thinking of using small bolts so that i could pull the stator off easily so i could pull the impellor out if need be. would this work?

thanks
ross

headhunter23

bolts(really small) will work... it really comes down to being able to pull it off when needed, ie clearing prop of weeds, greasing shaft etc. So you can go with stock or make something else.

Ivan.

grael

I don't buy mine, but the main difficulty with bolting, is getting access to apply nuts on the inside of the hull at the bottom. Just be careful not to strip the thread with screws, hand tighten the last bit gently.

This is the boat I made my partner's son, running with a 2cc ASP and my jet unit. Slower than mine.[8D]

DRAGONFIRE81M

you would only be able to apply nuts to the top two holes the two bottom holes go in to the intake scoop so only a screw can be used .

headhunter23

I disagree about need for nuts, the kehrer drive uses 2.5mm bolts, not the regular screws that u find in the graupner one. I would think you can use bolts and if your really nervous about it not having enough bite, get longer than necessary and put some epoxy on the other side if you see the threads and make your own threads.

Ivan.