Thursday, 20 October 2016

Steam power for the Big Wheel

The Big Wheel built from the 1927 instruction manual shown in the previous post, has been built following the printed instructions as closely as possible. Looking at it, bearing in mind its vintage, it was screaming out to be steam powered by a 1929 vertical boiler engine.

Tatty, yes, but it goes well and has that well used look about it
Rather than build the engine directly onto the model I decided to make it as a sub-assembly that can be easily fitted to the wheel using rods and collars. The also means the engine can be packed on its own, a much safer way to transport it. It may be tatty but it would be hard to replace, not to mention expensive, these days. We do have another engine in nicer condition but that is of the earlier type and still as the Meccano branding transfer on the boiler's outer jacket, something that would have been burnt off with constant use. This later, tatty version has the branding embossed and will survive for the life of the engine.
An overhead view shows the joining rods and gearing
A strip built base (you know how we like a bit of strip-construction!) was built using 9½ inch angle girders bolted to 5½ inch angle girders to make a frame. This was in-filled with 5½ inch perforated strips to form a base. The girders are configured to have the slotted hole sides making the outer walls of the base. A third 9½ inch angle girder is bolted through the centre to add support. Orientating this girder with the slotted holes making the fixing will ensure it will not protrude lower than the outer girders that form the frame of the base, thereby negating any risk of the finished base rocking on it.

Underside showing the third girder
A selection of gears were added, it is only a guess at this stage. I have also included a clutch that is held engaged by a spring. This can be held disengaged by holding the leaver back. The reason for this is with such a large wheel to get turning, a progressive take up of the power can be controlled by letting the clutch engage gently, like when pulling a way from a standing start in a vehicle with manual transmission. The wheel should start moving without the help of a push.  Well, that's the theory.  

The clutch assembly and final drive shaft
I did build a little 'Big Wheel' a few years ago and that could be started from a standing start without the use of a clutch. It was slightly smaller than this one. Below is a short video of it running on compressed air. There is a page about running steam engines on compressed air, for those times when it is not practical or permitted to fire them up, HERE.

I digress (again). The clutch is a simple affair. a gear wheel, as it stands now is a 50t gear,  is secured into one end of a socket coupling. A 1 inch pulley, fitted with a 'rubber' ring is secured in the other end of the coupling. This runs freely on the output shaft. A bush wheel is secured to the output shaft. A three-hole coupling is fitted with two, 1 inch rods and is tightened against a couple of nuts that have been locked together on a ½ inch bolt so it is free to rotate in the centre hole of a 3½ inch perforated strip. This strip pivots on a small  triangular plate, again via a bolt, lock nutted through the end hole of the 3½ inch perforated strip. The bush wheel is locked to the output shaft in such a position that the gear wheel is still in mesh with the pinion when the pulley and rubber ring are hard against it. The lever is biased against the bush wheel with the aid of a tension spring.

The clutch assembly and lever
The idea is the clutch is disengaged, when the engine has a full head of steam, and the flywheel is spun to set the engine running. once the engine is up to speed, the clutch can be gently let out and the wheel should slowly pick up speed - We will see tomorrow.

Another view of the clutch assembly
I have yet to design the final drive and chain tensioners, but it is almost there. I should have it finished tomorrow. In the meantime Sue has been building some extra gondolas to make it up to eight.

Sue is busy making and fitting more gondolas
Can you believe with all the blooming Meccano we have in this house we can't find another thirty two 2½ inch perforated strips in pre-war green? Well, we can't. So rather than use a lighter green, which would look horrible,  we have opted for zinc strips for now.  We should have it finished tomorrow and it will be ready for steaming. We will let you know how it goes.


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