A new engine for the model paddle boat Tanwen.

[Tony Bird]

Hi,

A little while ago I did a thread on a steam powered model paddle boat seen here on the pond at Winterbourne earlier this year.

A video at: https://youtu.be/ZgTk3ePlhjE

I was quite pleased with the performance of the model which uses one single acting oscillating steam engine driving the paddles through a gear box. It is quite exciting to control using rudder only and not being able to stop start or go backwards. Some time ago a friend gave me a lot of Mamod and replacement Mamod cylinders that are used on their locomotives; he said that he couldn't get them to work very well. So I thought I would try and get the cylinders to work and use them to make a prototype twin cylinder engine that would start, stop and reverse. The gear box to be used is the same design as is used in the paddle boat but with a lower gear reduction of 12:1 rather than 18:1.

I suspected that the cylinders would be too powerfully for the small hull of the paddle boat and in the event I was proved to be correct.



So it was decided to make a much smaller engine of a similar design, the cylinder size being a 1/4" bore and 1/2" stroke rather than the 3/8" bore and 3/4" stroke of the first engine.

The engine will be based on a small engine I designed years ago, this engine can be made single or double acting with bores of 1/4" up to 1/2", most built have been 5/16" bore all had a common stroke of 1/2".



The engine's column has been made of a light gauge aluminium square tube.



The port blocks and the reversing block with its valve have been made from some large brass angle that I have and was machined to thickness using a shellac chuck.



The small cylinders are fabricated in my usual way from some hexagonal brass rod and some K&S brass tube.








The K&S tube was soft soldered to its base and tippex (a correction fluid which contains chalk) was used to stop the solder contaminating the threaded hole.



The result of the first days efforts.



Regards Tony.

 

[Tony Bird]

Hi,

Some more work has been done on the engine. Flywheels have been turned and crank pins fitted.





The ports in the port block have been pilot drilled then drilled to size and some of the steam passageways have also been drilled.





RH pilot drilled LH drilled to size.




Regards Tony.

 

[Tony Bird]

Hi,

The worm and wheel for the engine arrived today and were fitted into the square section aluminium tube.



It was decided because the one end of the engine was so much heavier than the other the engine would be converted so that it was inverted. This means that when it is fitted in the hull the engines weight will be lower down and hopefully make the model more stable in the water. The two parts of the engine apart.



The two parts of the engine joined together.



All the steam passageways have been drilled in the port and reversing valve blocks.

There is quite a size and weight difference between the Mk.1 and the Mk.2 engines.



Regards Tony.

 

[Blogwitch]

Very neat design Tony, it should move your paddler along very nicely. People don't realise just how powerful these small engines are.

I should have thought about worms when I made mine, which used two steel gears. But they were for much larger models, so could take the weight.

John

 

[Tony Bird]

Hi,

As we are going away over Christmas only a bit of tidying up has been done on the engine today and it is likely to be the last work done on it this year.

Some relief was turned on the cylinders port face.



The cylinder bore and port face were lapped.





The plug holes in the port block were tapped the nut is being used as a depth stop.



Plugs were glued into the port block.



Some of the plugs were not cut back but used as securing points for the feet of the engine.



All the parts so far made.



That is it I suspect until next year, so everyone have a great Christmas and a Healthy New Year.

Regards Tony.

 

[Belugawhaleman]

Great work Tony!

 

[Tony Bird]

Hi,

I hope everyone had a great Christmas. *I got back into the shed earlier than I expected after our break, I didn't think we returned until tomorrow. *A design change has taken place. *The idea was to pack out the cylinders with some wooden lagging, it is something I have done before when using K&S brass tubing for the cylinders.



And.



However it was realised that using a conventional type of helical spring to hold the cylinders to their port blocks along with a spring for the reversing valve would take up a lot of room in the square section tube. *It would also make it difficult to remove the cylinders without taking most of the engine apart. *So it was decided to use an external spring to hold the cylinders against their port blocks. *A pair of Mamod cylinders using such a spring which is held in place by some K&S brass tube which is drilled and glued to the cylinders.



So some brass was turned and drilled to beef up the cylinders.



This tube was cut in half to make the parts required.




Tubes have been fitted into the reversing valve block to help its seal to the cylinder port blocks and the steam and exhaust pies have been soldered in place.



The engine has been test assembled and now looks like this.



The reversing valve next I think.

A happy and healthy New Year to everyone.

Regards Tony.

 

[Tony Bird]

Hi,

Today the reversing valve was made and its actuating lever attached.





With the reversing valve finished it allowed the steam passageways to be checked using a syringe and water.



The cylinder covers have been made and at the end of the day the engine looked like this.



A Happy & Healthy New Year.

Regards Tony.

 

[Tony Bird]

Hi,

I finished the engine today and it has run OK on air. The pistons were made and fitted with '0' rings.



The engine assembled looks lie this.








There is a bit of tweaking needed but nothing serious, I hope to run it on steam in a few days and will post a video. The engine running on air is more than powerful enough to power I suspected a larger hull than it will be fitted in. The engine is quite small less than 70 mm high about 2.5/8" and has a 1/4" bore and a 1/2" stroke about 6 mm & 12 mm.

Regards Tony.

 

[Blogwitch]

Very nice build indeed T.

It's also nice to see a 2 to 1 long stroke used, it should run a lot slower which is what you need for a paddler.

That is the same ratio I used for mine. The horizontal one on here is what I used to make for paddlers, it was just an easy conversion from the vertical one.