BR “Fell”
Well it seemed like a good idea at the time....
There is a pub in Derby that I frequent called "The Alexandria" it is an old railwaymans pub and at the back of the snug there is a picture of this locomotive -in all it's ugliness.
Very few people who drink there will have noticed its uniqueness -they will simply see an old diesel locomotive. But the Fell Locomotive was unique in that it had mechanical transmission and was designed to be a mainline express locomotive. It also had six motors, two of which were specifically dedicated to driving the “Rootes” style superchargers for the other four. This made it very noisy... But if you speak to a locomotive lover the one thing that sticks in peoples minds is, "that damned gearbox".
The Fell had the capacity to start on one motor and then add more, by clutching in, anywhere up to full power, all four motors. So, in theory if the Fell lost one or more of its motors, (which was fairly common in early BR diesels), it could still "make it home" on the others. What follows below is AN EXTREMELY SIMPLIFIED drawing of the Fell gearbox...
viz:
In the drawing above you can see the four motors and the four output shafts to the wheels and the coupling conrods and flycranks. In the centre you have the three differentials that "balance" the power load to the output shafts. Each motor is coupled to an output shaft via bevel gears. I have not included the four fluid couplers, (one per engine), for ease of drawing and visual simplicity...
The driver starts Motor A, this transmits power to it's output shaft and some via the upper differential to the B motor output shaft, thence to the gear coupled central differential and (finally) via the lower differential to the rear output shafts... Power is thus transmitted to the eight wheels and the whole lot moves forward. As each motor is "clutched in" more power is transferred through the differentials. The net result is that all eight wheels receive the same amount of power no matter how many engines are running and at whatever throttle or supercharge pressure.
The gearbox is preserved at The National Railway Museum in York -the rest of the loco was scrapped after it caught fire at Manchester Station. There are voiced opinions that the fire that destroyed the Fell was aided and abetted by the torque convertor fluid.
What destroyed the gear box was -an ingested loose screw...
When it was built, it was a 2-D-2 configuration, with conrods connecting all four driving wheels on each side. Later on the central conrod was removed and it looked like 2-B-B-2. It is this later version that I will probably build. This will allow me to cheat and pivot each twin sets of axles, so it will in actuality be a 2-B-B-2 rather than a 2-D-2. This will allow me to get the loco around the tighter curves that my layout demands, but most important of all -it will look stranger!!!
The reason for the change has to do with the high speed rotary resonance of the huge mass of steel conrods. By breaking up their length and moving the conrods to opposing sides, they lightened the mass, and more importantly, moved the resonant frequency -to a speed far higher than the locomotive was capable of.
My quest for authenticity means that it is going to have to have four motors and three differentials. I have some ideas on how to build scale torque convertors -but I have to admit the only ones I am familiar with have Borg Warner stamped on their side... It should be possible to construct a high viscosity vane and impeller system, but what exactly the working "thixotropic fluid" would have to be is at the moment, a mystery. Olive oil and beeswax dissolved in it is an obvious one -but it is somewhat of a fire hazard...
A few weeks have passed and I have been quietly researching. I have now come to the conclusion that this loco may be actually possible to build in Internal Combustion i.e. LIVE DIESEL. This will require the building of a liquid cooling system to cool the motors. AT LAST here is something that I can put all my years of work into -and be absolutely sure that it will work!!! There are several model marine diesel engines on the market however the ones that are suitable are down to three -fortunately they are all by the same manufacturer.
I have been thinking about the problem of the torque converter... The main problem relates to the formula that I have to use, this produces a result based on the thickness of the fluid N, the cube of the input shaft speed R -and the Fifth power of the diameter of the turbine D.
This means that for a thicker fluid I can build a smaller T/C, but the more limited the speed range that it will work through. The faster I turn the shaft the more efficient the T/C becomes. The wider I make the T/C the more torque that I can push through it.
HOWEVER....
As the physicist Joule discovered on his honeymoon, by measuring the temperature at the top and bottom of a waterfall, the motion creates HEAT and it is this heat that will be my enemy if I am not too careful. What I have to do is work out the widest diameter that I can fit within my loading gauge and then how to cool it. I am looking very carefully at the original "Voith" type of torque converter as it is pumped it fluids around inside a coolant water jacket.
The T/C will have to "fall out" of connection at idle and starting speeds of the motor. Once I am happy that I have the correct motor then, (and only then), can I begin to feed the figures into this formula. The "pumping losses" that are due to the "stall" and "fall out" speeds of rotation of a T/C are translated directly into heat -and these are the ones I will have to watch out for. I have found some interesting notes on an old type of automotive fluid coupler cum clutch, (which I had seen as a teenager in the South Kensington Science Museum) -The Smith Magnetic Clutch. In this the "fluid" was a suspension of iron particles in oil and it was "thickened" by the application of a electromagnetic field. this would have the great advantage that the "N" part of the equation I could vary to fit the requirements -with a rheostat!
How it works are the field windings magnetise the rotors on the output and input shafts and then the particles of iron filings then clump to it. The gap is rapidly bridged and the whole lot rotates as one. When the field winding are turned off, the clumps are then dispersed, and the input shaft centrifuges the iron particles back into suspension. I have asked the UK suppliers of my prospective locomotive engine to send me the details, It is actually a "Glow" engine rather than a true Diesel -but it should be quite acceptable!!!
Having sorted out the prospective motor -it being a two stroke then it should be fairly easy to design a tuned output exhaust system and the equivalent inlet system. However I am not at all sure how the universal gas dynamics equation will work for so small a system... What is also provides is the possibility of actually supercharging the engine, (but in a much more modest way!!!) This could be done via a ducted fan, (such as the ones used in electric model aeroplanes), pressurising the engine compartment. I doubt that I could get much above 20mm to 30mm of water pressure but that would be enough for "proof of concept" -in that it would be operating from a supercharged environment.
Well I now have the details for the Enya SS50 marine engine and I am quite surprised at how compact and powerful it is. The idling speed is a trifle higher than I would like at 2,500 RPM but given this simple figure I can now start feeding numbers into the equations. I won't bore you with the maths but the design brief is this!
Fall out Speed of the torque convertor is below 3,000 RPM (i.e it no longer functions) -this gives me a little lee way. If I make the fluid a known one (such as 30 SAE) then I can play with a fixed point on the equation/graph. The top speed of the motor is 16,500 RPM and I doubt that I would ever go that high so let us "Top Out" at 10,000. Ones and Zeros make the maths so much easier! This gives me a working range of 7,000 RPM. To sit my tuned exhaust and inlet system within this "Power Band" -is basic maths. I would like a fairly quiet engine so it might get the expansion chamber and resonator chamber treatment...
OK -here is the std "cheat sheet" for a tuned exhaust system for a two stroke engine. I wish I could say that I worked out all of the values -but this diagram has existed since the early 20th Century...
The first question is; "Just what is LAMBDA"? Well Lambda is the symbol used for the wave length. Thus if I want the system to operate best at a wavelength of 10cm or 3,300RPM the length of the inlet pipe would be 10cm. But that is too close to the stall speed of the T/C and I really want it to operate better at the higher revs. The peak power I have decided will be at 8,000RPM (or 5,000RPM above stall speed for the T/C).
This gives the value of Lambda to be 4cm.
Well I will admit I have been busy with other things and now at the end of the Financial Year -I can return to playing with ideas!!! The main problem with this loco has been that fact that the motor will be moving at thousands of revs while at idle and several more while at power. If this was a "nitro racer" then this would not really be a problem -however my loco has to start and stop very gently this means that it will require gearing down. Not I hasten to add by the gearbox of the original -but by a far more simpler 3 stage reduction.
The "theory" goes like this...
I feed the output from the Motor through my homemade magnetic clutch system and by varying the field strength I can have from 0 to 100% transmission. The output shaft then feeds the first stage reduction gear, this then feeds the second stage reduction gear located centrally between the two power bogies. The output from this feeds a central shaft to two Universal Joints located directly at the pivot points of the bogies. Then from here it feeds a worm and spur gear to the OUTER axles of the power bogies. The INNER axles are then fed power via the external fly cranks -in the exact reverse of the original manner!!!
The "maths" runs something like this
The First Stage reduction is 1:10
The Second Stage reduction is 1:10
The Worm and Spur Gear is 1:30
Therefore the TOTAL reduction is 10 x 10 x 30 = 3,000 : 1
This may seem to be pretty excessive -but remember that the stall point of the torque convertor will be 3,000 RPM.
Now, if we assume that we are running at 100% transmission and the driving wheel diameter is 5cm then the revolutions of the wheels will be 3,000 RPM.
The speed the loco will be travelling at will be 3,000 x Pi x 5cm per minute = 47,130 cm per minute. This rather alarming figure drops down to 7.8 metres per second, still rather on the high side, but this is a perfect case scenario!!! At best I think my clutch will be 10% effective -this gives a far more respectable 78cm per second. This equates to a "rough" 20MPH at scale speeds.
Well -slowly but surely things and ideas are starting to come together... Over the past few nights scribbled bits of paper with dozens of rubber marks have come together to produce the following "chassis mk1" drawing.
Everything can be welded together from 3mm plate stock(!)
I know that a few months have passed since I last made an entry onto this thread -but I have been busy -with home and work. I have decided to use the ENYA SS/50 Marine engine for my power plant. This is "slightly" overkill for a Gauge '3' model -but it is a very common IC engine and parts are easy to obtain. Experiments with the magnetic clutch system were errrmmm... "Interesting" as the amount of fluid and iron filings that were sprayed when the sides of the containment vessel breached were spectacular!!! I never even thought about the amount of force that the spinning oil and iron filings would exert on the sides of the clutch. I have come to a 3 plate clutch of the "wet plate" variety operating in a fillable oil bath. This closely resembles the "MekHydro" torque system, no I didn't crib the idea! But the problem is how to pump the oil that provides the frictive medium in and out of the clutch vessel.
I have found a source of wheels for this loco that are an exact match -but where they are from is probably correct too... The Driving Wheels are an exact fit for an LMS "Duchess" and the Bogie Wheels are an exact match for a tender for a "Duchess". I am not saying that BREL Derby had a few hanging around -but it does fit the ethos and manner of the Litchurch Lane Works!!!
The final part of the assembly drawings is now complete. I know how to make it reverse... This may not seem a major achievement but the reversing mechanism is one that has bothered me for some time. So, in my typical manner I decided to cheat. I have a design for a reversing mechanism that goes forwards or backwards whether it is going round -or not!!! I have decided to adapt the standard method of dog bevels. These do not transmit very much torque -but the system should only be going in reverse for short periods... The drawing below shows the arrangement for it.
As you can see there is a cruciform carrier at the centre which forms the bearing block for the three shafts. The input shaft drives the large spur gear which has one of the four bevel gears bolted to it. The spur gear sits on the output shaft on bearing and is free to rotate on it. While the loco is moving "forwards" the dog bevels rotate with the driven bevel gear and transmit torque to the last bevel gear which has the output shaft pinned to it. When the gear is changed to "reverse" there has to be some form of capture latch that stops the dog bevels rotating with the bearing block. This forces them to rotate -thus providing a reverse gear action.
This, (I think),, completes the power chain for the loco. What I now have to source are the pumps for the water and oil. These will have to be interdependently powered as the water pump will not only have to cool the glow motor but also the clutch system. It looks as if I will have to have ice cubes in the water coolant reservoir...
Models are getting completed thus other models rise up the construction ranks. This is what is happening with this model. I have the majority of the parts figured out and some of the prices. This is of course highly elastic as there have been occasions when I have worked out parts and suppliers only to find that, not only are the parts no longer made -but the supplier is now defunct!!! As this is a diesel model and will operate at a fairly high temperatures the bodywork is going to have to be made from metal. This is a radical departure for me as readers will know wood and plastic are more my medium. The body is going to have to made from Aluminium sheet. This is because it is light and very ductile. I have a small “fabricator” which consists of a Guillotine, Folding Break and Rolling Slips built into the one chassis. Whoever coined the sales term “light weight and portable” obviously never had to lift and shift this brute. I am not the puniest of people, but humping 45Kg around my small work shop is very bad for my back... Most of the time the fabricator lives on the floor on a slide out shelf, (I wonder why???), but for some jobs it has to sit on the top of the work bench.
Most of the body work is simple curves that can be rolled in the slips and there are some compound curves where the corners meet. But that is wooden dolly and sand bag work and can be formed by hand (hitting it slowly) with a “Repousement” hammer and a “Cloth and Hide” mallet. Joining the sheet metal sections is going to be “fun”. The normal tricks of soldering , brazing , and welding are not going to work with Aluminium. What I am going to have to learn is the magical art of “Aluminium Welding”. I put the brackets around the last part as my best friend refuses to call it welding -he is an instructor at “The Welding Institute” and he prefers the term “Eutectic Solvent Union”... Despite this I am going to use the words “Aluminium Welding” as, (to me), this is easier!!!
I will use non fluxed rods -in short the “Techno Weld Process” to create my shell that I will simply lift off and drop over the loco.
September -the start of the new school year and the start of this locomotive. Today is my son’s 11th birthday so the first order for the parts has gone out to the steel stock holders.
Bogies:
3mm bright mild steel flat
20mm x 50mm 2 rqd
20mm x 87.5mm 2 rqd
30mm x 115mm 4 rqd
Traction Chassis:
3mm bright mild steel flat
40mm x 300mm 1 rqd
50mm x 90mm 2 rqd
50mm x 30mm 2 rqd
50mm x 130mm 4 rqd
Power Chassis:
⅝" x ⅝" x 16SWG wall
500mm 2 rqd
120mm 4 rqd
After the accountancy job with the “Krokodil” I am loathe to do it again -because this is going to be the most expensive locomotive I have built so far.... But on the other hand perhaps it would make a good contrast to show what can be done on a restricted budget of £10 per week.
Ok -so what has changed in the intervening months since the design phase was “completed”?
Well, I have found that the manufacturers called “Super Custom” make a more suitable range of Marine engines for model locos than “Enya”. These range in size from 0.12 cu in to 0.91 cu in. All the calculations are for the Enya SS/50 engine -but the price comparison between the two manufacturers is “interesting” (!)
The 0.91 cu in motor is very tempting as a power supply as it has the flattest torque curve and slowest idle of the group.
All the fluid calculations were also based on SAE 30 automotive motor oil -which is for some reason is suddenly becoming very hard to find(?) The reason I chose this was its characteristics at all temperatures are well documented and there are no “additives” that change the viscosity with temperature as in a modern motor oil. Thus the viscosity at any temperature, pressure and rotation can be read off the graph. The alternative is to use good old fashioned Castor Oil as a medium for the torque convertor -but this will undergo oxidation in quite a short time interval... The other thing to consider is that the oil will be returned from the torque convertor looking like, and with the consistency of: dirty “whipped cream”. The pump will force cooled oil into the convertor and a large bore pipe will return the oil to the tank where it will separate and hopefully it will disperse back into oil and air. One of the things I am going to have to look out for is the danger of my model “exploding” in a sea of oily froth.
If I go for the 0.91cu in motor, (as now seems likely), then the cooling system will have to be adjusted to suit. The size of the radiator is going to be doubled -to two rows and there will be “tinselling” on the vanes to improve air to copper mixing. This also means that an Ice and Water tank is now a Definite rather than a Probable. Thus the direction of coolant air in the loco has to be reversed. Instead of blowing air INTO the loco I now have to blow air OUT of the loco. Initially I was going to blow a draught of air along the length of the loco -but it seems that there are going to have to be some auxiliary fans to do this whilst the radiator fan sits in a sealed environment. The electrical supply for them is going to have to be from a NiMH bank of cells. I know that I normally use Sealed Lead Acid batteries -but on this model I don’t think that is any room for them and the environment could be a little “hot”....
There is actually a design “progression” in my models. From this locomotive I learn about using a 2 stroke glow motor as a power plant for a loco and the cooling problems inherent with it.The next loco is a diesel electric in which I learn about the problems of building an alternator and the power bogies for it. The next loco is a gas turbine electric in which the only problems I now have to crack are those of actually making a working gas turbine since all that goes with it has been already been built!!!
As they say “I may be crazy -but I am not daft”