*delete M i k e u p delete*

Saddle pack the nimH, is a good idea. Are you going to solder end to end. Sentence structure for this old timer is not in the books, LOL. transmitter should be turned on first and off last. The esc has no on/off switch as I have a few Rc hydros ( Kunz ) for the brushed motors. Now if you know this stuff, disregard. Power for esc comes from battery after all else is hooked up. I use a phyton tx and rx with crystals. I have a few sets left ( crystals ). They don't make crystals any more as I've tried to get some and no luck in the past year. I have a Tear into that has never been run and is ready with lipo batteries. I got 2 lipos -size is 1300 and will be in saddle pack for balance. My jet is a modded one plus coupler, esc servo, cooling unit. Forgot on RC Groups, there is a thread just like this one on same subject. You could solder cells together close together and use velcro to hold in place. 4mm round connectors work great and rated up to 100 amps.

SicRC

Nice one Brian. Just so you know, when the instructions say to use CA (Super Glue... Crazy Glue etc) to glue the stator into the stator housing, don't even think about using anything else. You absolutely have to use CA for that job, nothing else will do. It's due to the type of plastic those parts are made from and the fact that there is so little contact area. Even if you think the world's most expensive aircraft adhesive would work, trust me on this, it won't. A few of us on another forum site have found this out the hard way.Yes, definitely saddle your batteries. Don't mount them permanently until you've run the boat at high speed. I think you'll be surprised at how far forward you're going to need the COG, it'll probably need to be just forward of the middle of the boat.I hope there's enough water over there for you to shoot some video, I'm really looking forward to the maiden Cheers, Steve.

redneckjetboat

has anybody on here ever paired one of those cox 049's with a graupner mini jetdrive?

SicRC

I've never seen one or heard of one that's been done, couldn't find anything on youtube either. It wouldn't be as fast on open water as a brushless electric setup but plenty fast enough for rapids crawling. It'd sure be a lightweight boat though

waspmike

More to the point? How much HP would one need from a small engine. 

SicRC

Plenty of power there Mike, especially since the overall weight would be a lot less than electric, just a bit low on RPM for flat water work. I agree about the mess of fuel... and starting issues... and potentially having a melted boat... but apart from that it'd be cool

waspmike

Ok. I'm a 2T guy at heart, so the idea of a screaming engine with a pipe. Yes we need what 18,000 RPM minimum?

SicRC

Yep, she'd be a noisy little sucker alright! Not my idea of a relaxing crawl session, but hey, whatever floats his boat

grael

I think it would be straining even to spin a 10mm impellor!

redneckjetboat

well i can build one of those things to turn 20,000 rpm or more, how many rpms would it take to get the boat up to say 25 or 30, im not looking for speed ive just always wanted to build a cox powered jetboat

pa38pilot

ESC problems in Kandahar. Applied all the components by the book, and no matter what I did, the ESCwould only run the motor in reverse (as in reverse stick only) , I could never get the ESC to give up the programming beeps and adjust any function dispite a dozen tries and manipulating all variables. Ensured batteries were charged.

I've run out of time on this continent. I am now in Kuwait... and I wouldn't let you guys down... the boat and all components are in my huge back pack for further testing and trouble shooting in my home town of San Francisco Ca, whereI'm headed for rest and relaxation.

I suspect a faulty ESC. I know where to take it to get my answers: Fransciscan Hobbies, Ocean Avenue.

Signing off from the desert.

Brian

sundogz

Brian, just swap any two wires on the motor and it will run forwards. No worries.

pa38pilot

I tried that every which way, and could get the motor to go forward, but the function is occuring by reverse on the stick, thus giving up a tenth of the RPMs The forward mode may only be available by my upgrading of RC Controllers. I' was trying to get the system to work off 25 year old RC gear. Either the RC gear is not compatable, or I bought a bogus ECS.

B

sundogz

Yes, on modern controllers you can reverse the throttle function with a switch on the tx. It doesn't sound like an esc problem to me. Most boat esc's don't have reverse function.

SicRC

25,000 would be good so build the fastest one you can. Keep the boat as light as possible as the Cox motor won't have much torque down low but once it hits it's power band it'll be fine.

waspmike

from what i can glean for the interweb.

Cox 049 propellers range from 30 x 1.25 through 80 x 4. 50 X 3 seems to be popular so the engine can rev sop it should have enough power

This does not take into account torque to accelerate but…

The only negative I see apart from carrying , fuel,, a battery for the glow plug, a starter, battery for starter ( unless you are old school) then making a marine flywheel etc is that Cox engine exhausts discharge on both sides so you will get oil everywhere. On the possitive side Cox engines supposedly run cool so you don't really need water cooling. Maybe a car cooling clamp?

I'd have both if I didn't live at the end of the supply chain, then see which one I got fed up with first.

(Not related to jet boats but I've always had a hangkering to try an build a "diesel" electric tug boat in which the electric power is provided by a constant? speed small petrol or nitro engine driving some form of small generator.)
.

mickieb49

 Not to rain on anyone's parade but has anyone actually tested the speed of a jetsprint  reving at 25+k as compared to one that is doing 15-20k?
  Jet units are not like a propped boat where you add more revs and it goe's quicker,  you try doing that in a jet unit and all you will get is more back pressure once you go over it's max range in RPM-thrust curve.  
 

waspmike

You have to match engine characteristics to the propeller. Be it aircraft or boat. In the case of Cox 049 it would seem that 21,000-ish is maximum so its within the charactristics of the jet drive I found stats for. But it is only about 200-220w so may never ever reach 21,000 with a jet?
With centrifugal pumps so maybe with axial pumps it is the volume moved that requires the hp, not the pressure. Then of course the nozzle may reach choked flow conditions? Cavitation not withstanding.

i have a lot to learn about jets!

It is easier to match electrics maybe because if too much rpm just use less cells! Then again RC throttles are adjustable just run less rpm.

Part of the fun would be trying?

DRAGONFIRE81M

I do know the mini jet will take around 50k @ 300w that's max with a little over kill 500 rpm being wasted . so 20k wont bet any speed record if that motor has the torque to get the rpm that hi
here is one of my vid of around 20k maybe more around 25k http://www.youtube.com/watch?v=ucsfqoBx3_w sorry my son was only 2yr in that vid

sundogz

Then there's the problem of being able to stop. That would require a clutch. And without a flywheel, it may stall as soon as it hits water. Not sure that it's worth the effort(s).

waspmike

Isn't that what a reversing bucket is for? Servo could be trimmed for neutral at engine idle.

It is not the destination but the journey. Ok getting philsophical now so I'll get my hat...

redneckjetboat

yep i guess ill just trash that idea, well i know where i can get a villain so i might jetdrive one of those

waspmike

DRAGONFIRE81M

yeah u could run a clutch but u will need a marine flywheel if not . learned the hard way there . also I did a nitro-v witch is the same hull as the villain . I should have a thread on here or even some info in here . http://www.youtube.com/watch?v=sYeKM...=TLR5phrzF50Og

redneckjetboat

on second thought the pro boat shockwave 26 seems like a perfect candidate for the 28 mm kmb drive, what do you guys think?