Cox powered jet-pump for model Sprint Boat

gkamysz wrote:The 15-16mm units advertised for 380 motors would be a close fit for .049 in terms of load.

My bad.. I'm waiting on a new brain via Amazon. The unit shown above has a 28mm impeller.. but there's another that I found, which has a 26mm impeller.

Some photos from the Amazon listing of the 26mm unit..

"Forward-only" config.



optional "reversing" capability..



kit contents..

rsv1cox wrote:My worry with this type of drive is that the water induction system will also pick up debris in the water and fowl the mechanism mitigating the advantage of no propeller.  

I'm sure it will affect my MRC boat in the pond behind my house.

It's my understanding that this type of drive is less likely to be fouled by debris that you might find in a shallow "pond". The intake-grate of your MRC "Mariner's" drive is there to help prevent debris from fouling the system.

(shown below-your photo)



Weed-ingress would likely result in their being "chopped-up".. rather than getting tangled/whipped around an exposed-shaft.

gkamysz wrote:The 15-16mm units advertised for 380 motors would be a close fit for .049 in terms of load.

Hi Greg, I searched Amazon this afternoon.. and found a pump-assembly to suit a 380 can-motor for $15.58

see here

That looks to be worth a try.. Thanks for the info. on the load comparison between brushless/glow-power.

rsv1cox wrote:I was thinking something smaller roddie that would pass through that grill, algie perhaps that is sticky.  But, I would think that the manufacturer would have done due dilligence in researching and preventing such a possibility.  We will see, maybe next spring Mark and I will try it out.  Right now half the pond is covered with ice.  

I am still figuring out a R/C installation.  It would be nice having an electric motor back-up.  

That Mariner looks like it would be a LOT OF FUN Robert!! MRC/Enya had it going on.. back when that model was new.

I'll offer you a tip... Always have a back-up boat.. to snare a gas-powered boat that runs out of fuel while out on the water. A purpose-built utility/rescue craft would be a fun project. I've often thought about configurations for such a vessel.

Here's a few photos (via Amazon) of the marine jet pump for 380 class brushed motors. (see my previous post for web-link)




The complete pump (less motor) length is only 4.01" (102mm)  .. and the unit's specs. state the "hole dia." to be 0.6" (16mm). This unit is designed for boats with a hull-length of between 12-20" (30-50cm)






I like the fact that the steering mechanism is built-into this type of drive.. and by design; is also less prone to damage from bottoming-out.. as compared to a conventional rudder.

The downside to this unit is the lack of a reversing-mechanism.. but my application may very-well be a single-channel RC (steering) with engine tuned to WOT. Reverse capability is not desirable.. under those conditions.

I'm taking a chance on it. I'll need to adapt a coupling for running a Cox .049 reed-valve engine. A 380 class brushed motor's "shaft OD" is 2.3mm. which is what the pump's existing coupling is designed to accept.. so I'd prefer to keep the "pump-side" OEM.. and devise a short flex-coupling to mate with what will likely be a custom flywheel for the engine.

So.. I figured I'd mess around and configure an engine for the pump.. which led me to this Babe Bee that Robert (rsv) sent me in the Fall of 2017.



... It has the earlier sm. web on the nose of the case... #6 dual-bypass cylinder w/milled wrench-flats... large-knob on the needle... "Thimble Drome" stamped on the tank-bowl..



Here's how I found it tonight..



The glow-head was with it.. but I had to find a gasket. I squirted a few drops of air tool oil into the top of the cylinder, on the head-threads and through the exhaust ports before installing the head. The compression is like new.. but I could feel some "slop" in the rod-socket joint. I have the reset tool.. so I'll be sure to make a note and tend to that.. as well as a total going through before a bench test.

Purpose-made flywheels for these engines aren't too easy to find.. but I was able to "make one" from some CNC parts that should work with an O-ring for a starter-belt. Then I rounded-up a Cox heatsink (Cat. #1970) and one of my mufflers (exhaust diverters) for a photo op.







I still need to work-out a coupling...

I received the jet-pump drives yesterday.. (Amazon delivered to my mailbox-curbside) but I found them today.. after checking tracking.

Sourced through Amazon; they were shipped from/by a person in the state of New York (USA) which intrigued me. (I've received items "sooner".. that came overseas) regardless.. I'm glad they're here; free from damage. Packaging was a bag within a bag.. (no box.. no bubble-pack)







The motor-coupler receives a 2.3mm shaft.. (I.E. 380 class brushed elec. motor) so.. if I'm to fit a Cox .049/.051 engine; I'll need a flywheel and step-down coupler from 1/8" (#5 machine-screw) to 2.3mm (3/32") on the engine side, for a solid-shaft drive. A collet and collet-nut arrangement for a flex-cable would be preferred.. but we'll see what comes along.

The pump-drives have two screw-together flanges. One for the "through the hull" intake-grate (bottom-hull amidships/astern) and one for the "through the transom" output-nozzle. Shipped partially assembled; there is a package of sm. (#2) sheet metal screws for the remaining open-points on the flanges.



The forward-side of the drive-housing has a flange-mounting for a 380 series brushed motor.. but I might utilize it for securing to an added "bulkhead" in my model.. for added rigidity.



Then there's a hose-fitting for cooling water option from the pump.



I don 't think it's crucial to have a "water-jacket" cooling-system surrounding the Cox engine's cylinder-head on a marine application. A coil of aluminum-tubing can be made to suit.. if need be.. but a Cox OEM heat-sink #1970 (a SandBlaster part) will sink-off a considerable amount of heat.. and it's simple; especially if the glow-head requires service. High-Nitro fuels also run cooler.. or so I'm told.

robot797 wrote:oh I would love to see this

also cant you drill a hole trough the sandblaser heatsink
and press a tube into it (make it a water cooler)

Hi Peter, Hopefully you "will" see something come together. I've been working on it.

Thanks for the idea on modifying the Cox heatsink for water-cooling. That will be added to my engine hop-up notes!

This afternoon I completely disassembled one of the drives.. to see how they're made.. and also to inspect the coupling.





The coupling's "output" side accepts a 3mm shaft.



The coupling's "input" side accepts a 2.3mm shaft. This is where I need to make a change.



I need the input-side to accept a 1/8" shaft coming from the engine. I could drill-out/increase the bore.. but I'd rather source the specific adapter-coupling.

I'm skeptical of the steering-range of the design. The "outer-nozzle" pivots left/right to direct the flow/thrust from the pump.. but only by a few degrees.. and I mean only a few. Nowhere near what I'd expect.. and I'd expect at least 22.5...  





The pump-unit seems pretty well-made. Brass bushings support the impeller-shaft at the front housing and inside the inner-nozzle at the rear. The drive-housing is too small to include a grease-fitting.. but was shipped packed with red-grease.





A prospective hull needs to be "opened-up" to accept the bottom-flange of the pump-housing. I'm thinking that a rubber gasket would be a good idea. I can make one from some .031" sheet silicone that I have.



A shaft coming from the engine..   There's probably better ways to do this.. but I'm trying to use what I have on hand.

I cut the head off of a 1" long 5-40 cap-screw and filed a flat on that end for a coupling. I was hoping that it would be long enough. It needed to come out of the coupling, and through my flywheel set-up.. and at least 1/4" into the the crankshaft.



Yes.. it was long enough. A single 5-40 hex-nut locks the flywheel against the engine's drive-plate with threads to spare.



The above image is of a leftover coupling from when I made some 1/2A electric-starters; using 540 series can-motors.

What you see on the output-side of the coupling, is Ace "EZ" nylon fuel tubing. It has a 1/8" OD. I like the idea of a semi-flexible link between two couplings; thinking that it may provide damping (no pun intended) for an IC engine app. It'll be as short as practical.. to keep the O/A drive-length as short as possible. A radio-box needs to fit forward of it.

Lots more to examine.. I bought two of these and one is missing a brass hex-nut for the steering-link. I probably have a spare in my metric hdwe. jar.

I also need to measure the distance between the bilge... and the center of the input-shaft on the pump. My Cox engine's output shaft needs to be as close as possible to this.. and hopefully (preferably) a straight-shot.

getback wrote:Hey Buddy your work is looking good I see a EOM pic there ! Is there no way to make the propusion tube move any further ? Dose it have stops that could bee improved for this / This is interesting and should bee fun this spring when things warm up >

Thanks Eric, My engines generally aren't "eye-candy" in the cosmetic sense.. but maybe more from a utilitarian standpoint. I cobble my Cox engines together to work.. so; polishing them up on the outside isn't something that I do very often. That said; I'll search for four of the same type (matching) screws to "mount one".... so as to avoid looking totally hack..

The steering (secondary) nozzle on this little pump may work fine the way it is. The little Sprint Boat that I recently bought seems to have a similar amount of travel to it's steering-nozzle.. although I haven't actually checked the max-travel L/R with the radio powered-up.

See below images; It's a very different animal than the two stand-alone pumps that I just acquired.... and uses a ball-end servo-arm which slides in a slot on the steering nozzle to move it L to R. The steering servo is mounted on its "side" and up-against the transom to accomplish this.  





Regarding the stand-alone units; I'll just have to see how they perform in the water.. to see if they will turn the prospective craft sharp-enough for my liking.

One thing is certain; the craft must be producing thrust in order to steer.

Mike1484 wrote:Very interesting project. I'm not a big interest guy on boats but I enjoy and admire your craftmanship and the fact that it is nice to see someone making good use of the wintertime to do some building. That boat should be a real hoot when done and i hope we see some action shots of it. I hope the unit survives the mighty power of the Cox engine!  
                                                                        Mike1484

Hey Mike! Thanks for your interest! I've been wanting to build a marine-drive for Cox .049/.051 glow-power for a long LONG time... but it always seemed daunting. Mainly the running hardware set-up.. but also the complexities of starting the engine.. throttling the engine.. etc.

I'd like to throttle the engine for this project.. but we'll have to see how much room there is in the hull. I've had good experience with the venturi (Ace plunger-style) throttle for the Babe Bee.. but that will occupy more space; forward of the engine's tank/backplate than an exhaust-throttle would.

The prospective hull/craft is something that I designed many years ago.. when I had access to a CNC machine and materials that were lightweight as well as buoyant.. (IE foam-board). The design will definitely be a test-bed for the drive.. because of its size and simplicity.

I made enough parts for a few boats back then..







Basically.. it looks like this when assembled..



or.......



Flat-bottom.. will likely require a pair of fixed rudders/fins on either side of the transom for directional-stability.. but I can add them later.

OVERLORD wrote:Here is a coupler 3mm /3,3mm

https://www.horizonhobby.fr/fr_FR/product/motor-coupler-3.3mm-motor-3mm-flexshaft/PRB286011.html

The make is proboat

Lieven! Thanks so much for the motor-coupler link.. however I had previously sourced the couplings I needed through Amazon.

They're on their way and I should have them on Jan. 15th.

Engine-couplings..



Pump couplings..

As mentioned previously; I cut a gasket from .031" sheet silicone for the bottom (hull) flange of the pump.. for when it comes time to fit it up to the hull.