Crabstick

75 pages of jetdrive stuff, so i decided to start this for the guys modding the "nqd tear into" boats

My Setup :

Tear into boat
3500kv 400 size outrunner
3s 2200mah lipo
Hyperion Titan 30a esc
GWS micro 6ch receiver
Digital micro servo for steering.
Custom brass coupler
Modded jet pump : have sleeved the bearing surface where the shaft runs through the jet unit with 1/8 k&s brass tube, sharpened the stator fins.

First run stock was quite pathetic, stock electrics are junk.
2nd run with the above mods - quite quick until an un harmonious vibration arose. On further investigation it turned out to be the impellor sliding back on the shaft, so i drilled a 2.5mm hole and tapped a 3mm thread and put the 3mm set screw through onto a flat i filed on the shaft
3rd run - Just nuts, this wee thing does 45/50kmh now, excellent handling and acceleration.

All in all im well impressed.

Next mod will be to go to a lower KV motor and/or try the 3500kv Motor on 2s lipo.

Simon.O.

It's Matt right??
Do you have any pics of this boat.
I do love the Kiwi way of hacking up stuff to go faster. Mr Hamilton did it once, and that was it. !!
Then there was John Britten, Tom Walkinshaw, and a few other famous Kiwis who knew how to get the goods out of a budget build.

Keep us (me) posted.

Crabstick

Hey Simon

Yep some pics, i will take it for a run shortly and video it had it in my mates pool yesterday, since the brushless/lipo repower its way too crazy for the pool though... haha

Simon.O.

Matt, that looks like a neat little boat and would do me nicely as a pond basher, where did you get it.
I hope it was locally "so it has low carbon miles"
No really I hope it was locally so I can get one easily too.
Keep us posted and as you know vids are always welcome even though I can not do them yet.
Cheers.

DRAGONFIRE81M

here you go man ill give you a boost on this one . you can get them on ebay heres a link to one http://cgi.ebay.com/New-Radio-Contro...d=p3286.c0.m14

look around you can find them for diffrent $ some even have name your lowest bid . theres even one that some one has already cut open for $55 .

Crabstick

Ah Simon, i will put you in contact with the guy i got it from off tardme. much easier and cheaper than getting through e-bay. i will PM you his details.. at 80$ nz its a good buy.

for around 100$ usd you can get a BL/lipo/esc and Charger

Crabstick

The intake for the pump has this drop down plastic block that can be totally removed from the unit giving access to impeller and shaft without removing the jet, this hangs down as a water trap a little, but inside it also has a square step that cannot possibly be good for flow into the jet, it is only 3mm wide but none the less a step where water entering the unit will be hitting creating drag and thus rubbing me of speed.

Will take a vid of the little beastie after work tomorrow

for some reason shipping from US to NZ is crazy prices, but shipping from say china is way cheaper.

damfurst

Hey Crab, I too have a NQD jet boat that I have started modding. I took everything out and replaced the jet drive with Graupners mini drive. That let me run a 550 motor that I had on 8.4v. I know that my setup is quite heavy but speed is not my main objective at this point. Any way I'm glad to see a thread just for this boat and will check back from time to time. damfurst

headhunter23

Hey dam, the drive ya replaced is pretty much an exact duplicate of the mini graupner, only improved upon in terms of minor differences... although I can't remember the graupner is sleeved... I don't remember seeing one on the unit(I think they're larger units are sleeved). Anyways it's just as easy to throw in a piece of brass on the knock off drive.

Ivan.

DRAGONFIRE81M

the nockoff is 1mm bigger and both doesnt have bushings . but you can run a bearing on the grupner . i have the part# in the jet thread posted twice . and the motor mount is better on the nockoff even though it is a 28mm mount . the grupner is weak and will brake in half . but that doesnt make it trash you can cut the mount off and use a alum angel mount .

Crabstick

Going to put the GPS in the jetboat tonight and get a speed reading, for me its all about speed since im an Avid racer :P

headhunter23

hope it's the geko... too much weight with real gps, I had run a boat beside knock off, approximately 20-25kph, more speed available without grate.

Crabstick

yeah the etrex unfortunately my gecko went bye bye into the drink, was taped on top of my rigger doing 55mph, it decided to come off... DOH the etrex is a little heavier but oh well.

Yeah the grate was the first thing i removed, going to flow the intake a bit and see if i can get a bit more out of it.

headhunter23

Not sure if ya read it but dragon and a couple guys made custom smaller exhaust jets to get increased acceleration and cornering. not sure if it helped top end. The drives do max out, I've maxed mine on 11.1v with 3200rpm with grate.

Crabstick

well it did 43kmh on GPS, not bad really. Managed to borrow a ghecko off my mate and put it inside the boat instead of taping the E-trex to the top

Couldnt do a video as it was raining didnt want to get my phone wet

This weekend I will flow the intake out - More in - More out..

I think sharpening the inside of the stator fins and cleaning up all the burrs on the impeller was a bit of an improvement

How do you know its maxxed out ? Have you guys done any testing as in Litres per min to quantify the changes the mod is making?

headhunter23

Keep putting more power to it, no change is *****g it out. Nice numbers, was wondering what it pulled without grate. Big difference.

Ivan.

DRAGONFIRE81M

headhunter right there is a max . theres a point where you can only flow so mutch water throw the impeller . when that happens it backs up . you can also over power and make it slower by actally splitting the oxasgn and couseing the drive to airrate

Quicksilver

ok, I'm gonna try here, The maximum output velocity of jet drives are directly related to intake gullet rake and volume, as well as intake area. Then the other variables, impeller efficiency, pitch, venturi shape, size and output area. On top of the drives capabilities, boat design is key, dead rise, how wet the hull runs...on and on.

The key principle and this is tough to wrap ones brain around is this, a boat or aircraft can only go faster if the output velocity is greater than the intake velocity. So simple... nope this means if the jet cannot accelerate the water faster than it comes in than you go no faster. With an impeller with a certain pitch, you can only accelerate water so fast. Since this is not a surface drive where the boat is riding on a blade, you put that prop in a tube and speed it up, eventually bubble will form on the leading edges of the impeller and your efficiency will decrease. These bubbles stay in the duct unlike a regular prop, so the jet stream aerates due from the impeller cavitating. Further more the only way around this, is complicated. Almost bordering on bioengineering. The intake and outlet of the venturi must be variable or the impeller must be variable pitch.

I'll leave it at that for tonight, but it's still not this simple at all. I've written this out so many times and it doesnt get any easier. This one is pretty good, at least to me. Try searching around, not much info out there on the theory behind water jets or should I say beyond the simplified theory.

food for thought.
http://en.wikipedia.org/wiki/Jetboat
here's a big one, but I recommend anyone interested in jet pumps to read through this whole thread
http://www.boatdesign.net/forums/showthread.php?t=11254


ooooo found something related a neat chart...notice thrust has to go to zero [:-]
So the next thought which you've already started thinking about is how to go faster......that second link goes pretty in depth with that

Crabstick

By flowing the intake i mean smoothing out the casting lumps and the big square edge thats on the back wall of the intake. Im also thinking of experimenting with vortex generators on the intake..

Thanks for the post quicksilver, Interesting about the variable pitch impeller, my guess is it would be exp to manufacture and maintain on the model jet unit though.

id like more info on Bioengineering in the jet unit?

Quicksilver

I've got to find all the sites, but it's basically a concept that you can change the intake size and shape using flexible materials. Which on a large boat is no easy task...a lot of its theory and some of it is in the design phase. I say bioengineering, since theyre trying to use these materials in a way like no other. The material would have to be controllable.

DRAGONFIRE81M

to give some of my thoughts on increaseing speed . i tryed to do it with smaller nozzles . but really it doesnt work that way b/c the flow just backs up and comes out the sides . to increase water speed it needs to be done in the stater area then dricted throw a smaller nozzle

Quicksilver

correct! this is why I'm thinking of building one. The hardest part imo of building a jet unit is the venturi aka bowl, that holds the stator. I'd love to use aluminum, but since brass is so easy to work with, I'll probably use that.

The whole idea is that at higher speeds the intake should be smaller, and the output should be smaller, problem is, you're increasing pressure, so at lower speeds, you'll be less efficient, since you wont be ramming water in like at high speeds. This is where the variable intake comes in.

I've got a question could I use two radios in the same boat on different frequencies. I dont know if they still interfere due to proximity. This way I could experiment with a variable intake and output. I want to make a square boawl and nozzle so making is variable is easier. Would kind of be a test mule.

headhunter23

If your testing jets, make a little dounut shaped tub, mount jet against cheap weight measuring stuff, fill tub run jet measure. Would be easiest way to screw around and test. But if you really want the 2 radios in boat, yea u can do it, would probably be better if one was on 75 and the other on some other, but I guess it also depends on radio. I got rid of my other radio went with airplane(spektrum 2.4 dsm2) radio so no glitching etc, can stick 2 receievers on same boat no problems.

Ivan.

Crabstick

ah I see, I thought by bioengineering that you were referring to atomizing the water changing its molecular structure in the jet or something lol.

I have a few things i want to test on this little unit :

Litres per min to measure volume. - was thinking of making a tray to feed 10l of water into the jet and measuring the time taken to pump the water.

And force - Headhunter - exactly what i was thinking using the wife's kitchen scales

once I have a baseline for both, I can do some mods and quantify them. - they may be worse, may be better, least though you can measure and compare

on *****g the jet out - feeding it more power may have increased RPM , but likely reduced torque.. would be interesting to test a few diff KV motors with the above tests.



on the two radios, as long as they frequencies are separated by .100mhz it should be fine. that said I would use a toroid (choke) on the esc lead from the RX.

I have a 6ch radio from my heli that could be used to control an adjustable screen to cover some of the intake. im not going to wast time on this little boat doing that, but might order a big ass graupner #5 unit and build a jetsprint boat to suit.

DRAGONFIRE81M

i did this two would like to know what you come up with . but i got a max throust of 16.86 oz