Cox powered boat litle shrimp hidroplane

1/2A Nut wrote:Best wishes on the project, looking forward to your results.  

Here is a pic showing the standard Dumas flywheel for submerged 1/2A props.
The other was milled using a lathe and is also steel, less load on the ball socket
and ideal for surface prop use for rpm up to 29k. 19g less in weight.
Tested with .05 and .07 car motors thus far. Note bearing thrust washer.





 

Thank you, it’s cool to have tricks from the pros I didn't think it was necessary to use a lighter flywheel but for clearance reasons I think I will have to make a custom one.When you say the ball socket. so you use a join? what type??Or should I say where I can find one? Do you have a photo of the ball joint you use? I haven't started building the boat, I made another cooling jacket exhaust manifold yesterday


This one is designed so as not to have to modify the cylinder I had to take my time to get it right, it was more difficult than simply modifying the cylinder I think I can make a couple of them . for those who would want one

Yes, the engines ball socket.

With the right prop the load will be reasonable and won't need to be
reset very often after the first reset. What size prop came with the kit?
The prop can be modified to run with a TD engine.

If you seek a good metal prop they are out there to modify, example here
a Octura 0930 reduced and ran with my Picco .05 very fast instant speed at launch.


Cut / balanced Octura 0930 to 0924 made a 38 mph pass.

To get started I think I can use the propeller which is in the kit it's a 1.4 x27 ?? Ha The ball joint of the motor I had understood something else I thought you were talking about a joint between the motor and the flex cable I wonder if it would be necessary to have a joint 1/2A Nut i saw that you have what looks like a big trust washer on the engine.???

I think you would want some sort of thrust bearing in the outdrive. I don't think a flex shaft would transfer thrust loads that well, plus they tend to wrap up under load. At least that's what I remember from 1976.

You want to use a thrust-washer between the front of the engine's crankcase and the drive-plate because a marine prop is a "pusher".. which applies pressure on the drive-line. I believe that there were "phenolic" washers available at one time. Dumas sold their 1.0" diameter propellers for Cox .049 engine-power. That would be equivalent to 25-26mm.

706jim wrote:I think you would want some sort of thrust bearing in the outdrive. I don't think a flex shaft would transfer thrust loads that well, plus they tend to wrap up under load. At least that's what I remember from 1976.

Yes it is true that the flexible cable under tension make it shortens but also tightens and stiffens it  But normally the pressure should be between The thrust washer and strut    
Also Using a ball joint coupler Helps to have the cable floating. But to shrink under tension without really applying pressure on the crankchaft trust washer I would like to use something similar to this but I don't really know but I think it's really necessary



On a larger boat that I modified I used a flexible drive schaft and  ball joint link
It was with this boat that I learned that those flexible cable shrink and that it is better to leave the space necessary for shrinking of the cable too loosely it would vibrate terribly and too tight would deform the stufing tube and loosen the connection between the wire drive and The engine This little joint is not just for changing the angle Obviously finding this part for a Cox engine is almost impossible I'm going to have to improvise something

Yes it is a thrust washer with bearings.

The load on the engine from the rigger and the prop may require a modified
1.4x27 in order to not bog down the engine and stop at launch.
Of course try the stock prop as is, RC gear is very low weight these days.




Cox 80w Dumas 1/2A submerged prop comparison to select smaller / lower weight strut and kickback rudder.




I use wire drives to keep the weight / mass off the engine otherwise you waste
too much power swinging mass and not pushing forward. Teflon tube is used to
protect the .062 wire.  

Some links,
https://www.rcraceboat.com/Storewiredrive.html
https://www.rcraceboat.com/StoreCoupler.html

I just sent Jeff a email for two steel collect couplers for 5-40 thread and .062 wire drives 1/8th stubs.
This not a stock item, he does custom size requests.

1/2A Nut wrote:Yes it is a thrust washer with bearings.

The load on the engine from the rigger and the prop may require a modified
1.4x27 in order to not bog down the engine and stop at launch.
Of course try the stock prop as is, RC gear is very low weight these days.




Cox 80w Dumas 1/2A submerged prop comparison to select smaller / lower weight strut and kickback rudder.




I use wire drives to keep the weight / mass off the engine otherwise you waste
too much power swinging mass and not pushing forward. Teflon tube is used to
protect the .062 wire.  

Some links,
https://www.rcraceboat.com/Storewiredrive.html
https://www.rcraceboat.com/StoreCoupler.html

I just sent Jeff a email for two steel collect couplers for 5-40 thread and .062 wire drives 1/8th stubs.
This not a stock item, he does custom size requests.

I would like to have your opinion on the flexible cable, do you think it is worth trying? it Or I would be better off using wire drives? I would like to reduce the motor angle as much as possible Also what do you think of the dog bone type ball joint? ?not a wire drive couplers I would like to avoid having pressure on the engine thrust washer And seems to me the joint is an effective solution and Allows me to reduce the importance of having the motor perfectly centered with the stufing tube of the cable And will give me the necessary play clearance It is certain that once tested I could always change the drive cable if it is not sufficient a hard chaft would be more effective less vibration

One fact often overlooked with the dog bone style universal that if it is used alone it will vibrate like crazy if the shaft angle change is anything but zero degrees. It accelerates and decelerates four times per revolution. To get around this, the dogbone is used in pairs so only the center section is under this acceleration. The amount varies as the reciprocal of the cosine of the angle of deflection. (Did this as a university project in 1974).
So if the angle between the engine and shaft is small its a good idea but not if it's noticabley large.

3mm or 1/8" flex cable is ok if you don't mind the mass and the dia. surface contact drag.
A 2mm collect coupler tapped to 5-40 would be the only best solution with cables.


For me I would not use any heavy mass past the flywheel where possible with the TD as it has
an aluminum crank case and will wear out fast with a boats poor unbalanced coupler etc.
I have dealt with the bad using vintage Dumas flywheels and brass couplers. It did get
the job done to make water runs but sacrificed the crank case. Wore out two TD cases
and 1 Queen Bee case. The brass dog bone coupler took out the cases. The steel pin
in the coupler ball wore into the female side of the coupler. Steel slapped against softer brass.

Note regarding engine angle - a tilt in the engine allows flow of oil to gravitate down
soaking the aluminum case reducing wear from vibration imposed on the steel crank shaft.

Bottom line use what you can stomach and understand the pros and cons. If you want
a higher performance fuss free runner only the best solutions will do.

TD .051 rigger size estimate in comparison to the Picco .05 rigger / 43mph


 

1/2A Nut wrote:3mm or 1/8" flex cable is ok if you don't mind the mass and the dia. surface contact drag.
A 2mm collect coupler tapped to 5-40 would be the only best solution with cables.


For me I would not use any heavy mass past the flywheel where possible with the TD as it has
an aluminum crank case and will wear out fast with a boats poor unbalanced coupler etc.
I have dealt with the bad using vintage Dumas flywheels and brass couplers. It did get
the job done to make water runs but sacrificed the crank case. Wore out two TD cases
and 1 Queen Bee case. The brass dog bone coupler took out the cases. The steel pin
in the coupler ball wore into the female side of the coupler. Steel slapped against softer brass.

Note regarding engine angle - a tilt in the engine allows flow of oil to gravitate down
soaking the aluminum case reducing wear from vibration imposed on the steel crank shaft.

Bottom line use what you can stomach and understand the pros and cons. If you want
a higher performance fuss free runner only the best solutions will do.

TD .051 rigger size estimate in comparison to the Picco .05 rigger / 43mph


 

 Yes I understand A 2 mm conection  coupler tapped at 5-40 would be the only best solution but I believe I can avoid the pressure on the engine housing and the thrust washer i want That the moving part would be supported by a ball bearing the part would be free to move forward and backward I ideally want to avoid damaging the engine is a .051 it is new freshly out of the box never run I would really like to avoid directly connecting cable or wire to the motors. I can balance the parts to avoid vibration.  I think hard wire drive would be even better!  regarding engine angle - a tilt in The engine position will be present just very slightly different More for clearance reasons but to avoid a slight misalignment which could wear out the engine casing ???But I also wonder about the wire I'm afraid that the motor is at risk of breaking the crank pin If it is too direct!. The flexible cable can absorb the shock This is one of the reasons why I would like to use it I think I will still order a wire like you suggested at the moment it is the design of the boat that I am questioning I may have to build one entirely from scratch mabe I can use a Cox .09 rc which I would modify if the shrimp model is too big for the .051 Currently I am working on building a new water cooled exhaust manifold. Cylinder jacket
For the unmodified cylinder of the .051 also for those who would like one

Maybe consider an aluminum flywheel for less load on the crankcase bearing. I can make one for you

706jim wrote:Maybe consider an aluminum flywheel for less load on the crankcase bearing. I can make one for you

Thanks for the offer jim but I already have some models that I can use but also I have what I need to make some There remains the design to consider I have already tested a very small model with little mass but on a car it worked very well but I fear that for a boat the ideal weight in aluminum would be bigger than the one I have on the car but I need to be able to place the engine the lowest possible
I think I will modify this one Make a wider grove and Balance the piece it Can be finished at the end in the shape of a cone I will possibly make a similar size one in aluminum

I found another small boat that could possibly be powered by a Cox engine. I think I'm going to need more free time if I want to be able to use al of them this year So I'm going to start by using it as it is.    I ordered a pnp version for less problem with finding the right parts when I'm going to finish with one and I'm going to have a  boat ready I'm going to start modifying this model I think it would be nice to be able to change the motor from thermal to electric and vice versa

 
I'm planning my summer on the dock I recently purchased a 30 foot yath


It's like a little second home  so I want to have some quality time on the water And since we can't always have the boat running, we're going to have fun on the dock wit the rc boat

Darn Nice Yacht That is where my fun would start LOL hope you get the boat figured out as not to mess the engine up / I don't know much about the boat Sean .

That 15" hydro should do good with the TD .051, Yacht looks like some good solid fun there!!
Your improved water jacket and exhaust with no mods to the cylinder is really a great route to go.
Have you water tested with a gravity feed for leaks during running? Look forward to seeing what is
possible with the 15" hydro, let us know the bare weight of the fiberglass hull and hatch, guessing 6oz.

I added a radial mount to the back of the TD as a "radial cooler" should help to disperse heat.
Beam mounts to mounting blocks to the hull. Sourced a Tarno RC carb will also help move heat.


Leaner 21" L TD size rigger for flat running on calm pond water.

I will carry out performance tests with the engine but with an airplane propeller To see if I have a good result with the exhaust system I would like to see if I managed to have a gain in power And it will be easier to measure with this configuration .The exhaust manifold is better adjusted with the flow of the cylinder the outlet of the gas Is freer bigger and should improve the exhaust flow Compare with any model the gas passage is not greater between the cylinder and the jacket but the exit to the tube is much larger than a over size gtp collector Or even this red model that I had modified to be bigger than those of the gtp The tube is securely riveted in place, impossible to turn quickly tested the watertightness of the water compartment without having to install it on an engine. I believe that the modified cylinder is not leaking but I will revise for a conventional model without modification. I think I'm going to do the same thing but separated into two pieces would be easier to seal the two compartments  Another aspect  That I want to keep of my first model is that the water is far from the glow plug so as not to cool it too much.

may have found a solution to prevent the shaft from pressing directly on the motor. I found a joint that allows free movement between the motor and drive shaft and allows for slight absorption dampenig efect
This should resolve any slight misalignment problems. Its design should not vibrate like a drive join would it is a 3.18 x4 i have a 4mm pilot chaft for a .061 norvel car modified engine that fit the cox crankchaft

Pretty well known fitting in the US A love joy coupler found in log splitters and applications where engine to pump is required .. They need to bee straight with each other if not will wear on the rubber /nylon ? Insert and then the fingers on the boss . Surprised you found one that small

getback wrote:Pretty well known fitting in the US A love joy coupler found in log splitters and applications where engine to pump is required .. They need to bee straight with each other if not will wear on the rubber /nylon ? Insert and then the fingers on the boss . Surprised you found one that small

yes i spent a lot of time looking for something compatible at a good price. I hope this will work I will align the motor as straight as possible and have a small space for the forward and backward movement of the shaft This is really why I use this parts Unlike a universal joint, this one should not transfer vibrations to the motor and dampen it. I believe that with a bearing behind the coupler everything should be solid and eliminate the vibration of the flexible cable The part of the cable which will be in the collar and a ball bearing wit lube fiting the cable tip will be reinforced with tin soldering so that the end is rigid

Here is the other beautiful little boat smaller but more expensive but would be able to insert the small motor on board I placed it to see if I could close the cover and yes it fits The boat complete with motor ans esc almost  ready To run  without battery or receiver. weighs 476gram A lot of this weight is the esc and the brushless motor I can't wait to try it as is with the brushless motor. On 3s


I'm going to get a second one, I think I'm going to want to keep this one original I gave myself a gift it was cheap and I needed new receivers I wanted to find a waterproof receiver model for boats and as I have several I found An inexpensive one that had the possibility of using waterproof receivers, the flysky fs-gt3c For a cheap controller it doesn't seem too bad it's good to have a usb rechargeable battry pack then also tink it's possible to use an external battry pack to power it Of course I could just buy a new receiver for my spectrum controller but I wanted a different one that had less expensive receivers and the cost of the controller was very close to that of a spectrum receiver

I'm loving these RC model boating projects David!!!

The engine looks proportional with the hull this should be a really great IC project.
Elect is too easy but still fun as you get to wring out the boats abilities and learn
how it handles for the surface conditions at your particular pond.
As a E boat it is heavy for it's size at 16.8oz less battery and RX.
1/2A hydro should be much lighter without the E gear. Yet at 3S
it should move out in the low 40's What does the bottom of the
hull look like? Sharp riding edges?