# Mattress Wallpaper Time?



## ralphbrades (Jan 3, 2008)

As several people know -I cannot devote much time to locomotives at the moment due to domestic issues. However this does not stop me wondering... I have a book called "Locomotives that never were". In it (chapter 17) is a drawing of an LMS 2-D0-2 electric locomotive. So far so good you may think -but this is an adaption of an SBB Ae3/6 (!) a 2-C0-1 design... For some reason I find it very appealing. I have built an SLM designed loco for the GIP built in the UK -so I am OK with the weirdness of it. The problem that is driving me crazy is the fact that (as with all of my locos) they would have to work as near as possible to the original method as possible. This means working out a *"Brown Boveri -Buckli" *drive system... Now I have built a "Quill" drive loco -that was mathematically "interesting" to say the least...

This is quite frankly going to be horrible!!!

But I am quite practised at using a slide rule with one hand -right handed and if that fails me I have my trusty Sinclair Scientific (which I built myself as a poor penniless student).

This an SBB Ae3/6 http://de.wikipedia.org/w/index.php?title=Datei:Ae_3-6-I_buchli.jpg&filetimestamp=20060919212035 

You can see the BBB drive mechanism on each of the three drive wheels It is an external gear driven system with internal compensation to allow the central axle to float up/down and for torque effects to be removed during accel/deccel phases. One of the problems with a Quill system is "Wheel Hopping" as each side of the axle is stressed differently (one set of springs wind clockwise and the other anticlockwise) during these phases. This is not a problem with a BBB with its internal struts and compensation levers.

http://en.wikipedia.org/wiki/Buchli_drive

I will post how I am doing here over the course of the next few days and weeks. It will keep my mind busy if nothing else!!!

regards

ralph


----------



## Greg Elmassian (Jan 3, 2008)

That is an insane drive setup! I don't quite get where the imbalance at high speeds comes from, unless the parts with the levers are actually turning... 

Greg


----------



## ralphbrades (Jan 3, 2008)

*Everything revolves* Mr Elmassian. 

Tractive power between the external large gear and the wheel passes through both of the bars. Vertical motion of the axle through the hornguides is allowed by the flexing of the two meshed levers. There is NO vertical motion compensation when the drive system is horizontal -thus the dynamic imbalance. However this also means that the drive can compensate for irregularities in the curvature of the track whilst the drive system is horizontal. The system constantly changes from vertical motion to horizontal motion whilst cornering. The main design problem is the fact that all the motors tractive effort is taken through the two pivots for the meshed levers -thus one is compressed whilst the other is in tension. 

regards 

ralph


----------



## Greg Elmassian (Jan 3, 2008)

I think I'm getting it a bit.. the illustration was a cutaway and did not bring forward the operation to me very well. The wheel and gear turn at the same time, although coupled through the 2 levers. 

I still don't visualize the change from vertical to horizontal. It appears that the disc of the gear and the wheel disk are in parallel planes... so still not "seeing" it. 

Greg


----------



## ralphbrades (Jan 3, 2008)

The large gear is mounted on the chassis of the loco. The *undriven* side of the axle is mounted in hornguides, the *driven* side is mounted in a pillow block bearing. However the driven axle axis centre and the gear axis centre *are not co-axial*. This allows the driven axle to move up/down in the grip of the transfer bars, (vertical in the Wiki drawing). Thus no weight of that side of the loco is taken through the bars to the bearing used by the large gear. The external gearing allowed service crews to quickly change over worn gears and access was of course no problem. It has a fundamental problem in that it does not translate well to a smaller size. What is going to be "fun" are scale sized transfer bars and meshed levers. Typically I would have made them from brass -but it would be too weak. So, it looks like I am going to have to 316 or 310 stainless steel to make the system out of. The large gear I would opt for Hostaform, it is unbelievably messy to work with but it cuts and taps well. 

regards 

ralph


----------



## ralphbrades (Jan 3, 2008)

Ok. The rough calculations are starting to appear out of the Aether! I have elected to use an RE-540/1 motor by MFA. This (usefully) has a torque rating of 1,000 Gramme Centimetres. Given the size of the driver wheels I have opted for a MOD1 12 tooth and a 50 tooth gear system. This will produce a torque at the centre of the 50 tooth gear of 6,944 Gramme Centimetres. All of which means -*keep your fingers well away from the spokes....* 

Moving away from the centre of rotation means that the amount of force is lower but the problem of transmitting all that torque still remains. 

The thickest rod that I can easily fit in the slots that will have to milled into the 50 tooth gear is between 2mm and 3mm -and for the ease of milling the slots in the gear wheels a 2mm rod would be better. I had hoped the 316 or 310 stainless steels would provide me with enough strength -but the answer is resounding *NO!* from the slide rule. At the point of connection between the transfer bars and the lever arms the pins are subject to a shearing force of 4,165 grammes. This quite effectively rules out the majority of stainless steels that I can easily get hold of. The one remaining alloy that is strong enough(!) and I can get hold of is the one I detest using!!! This is "Silver Steel". It does not solder well and has to be BRAZED and it is fussy about the quality of the Spelter and Flux too. 

This will mean turning a solid steel wheel for the driven side with a spoked wheel for the hornguide side. There are a number of companies selling a cast iron spoked wheel of the right size -however I have always found turning "grey" cast iron a very messy experience. 

regards 

ralph


----------



## Semper Vaporo (Jan 2, 2008)

Hee hee hee... you are sooooo far ahead of me!

Right now I'd take one made from Papier Mâché and held together with spit and bubblegum just to get something in my hands to figure out how it works!







I think something went "fizzle" in my head last night when I tried to figure some of the mechanics of it out.


----------



## ralphbrades (Jan 3, 2008)

Well judging by the e-mails from other people -you are not alone in this!!! Basically they all ask the same question *"How in GODS name -does this thing work???"* Well I have decided to do some "doodles" showing the mechanism in each quarter revolution hopefully this should explain what is happening as it is actually a very cunning piece of design. The main problem that has reared its head this afternoon are the meshed levers. These are the small levers that compensate for the non co-axial movement of the driven wheel. These are held still by the opposing forces on them. The forces directly impose on the teeth of the meshed levers in opposing directions. In short these little things have to take TWICE the torque of the wheel. And do it without the toque ripping the teeth out.... If I use a standard steel gear alloy EN30B then "The Book" says that I could go as low as MOD 0.5 for my teeth provided they are at least 4mm thick. However the finer the mesh -the more that dirt can foul the mesh and remove the compensation effect(!) The bigger teeth will be stronger but would not have as many teeth in mesh and thus be less prone to dirt ingress -but having fewer teeth in mesh means a less accurate compensation -i.e. *the teeth rattle*. MOD 1 is I think too large and MOD 0.5 too small -so after having poured over the specs I have decided to go for MOD 0.6 

regards 

ralph


----------



## ralphbrades (Jan 3, 2008)

Ok. If you study this picture then the next doodle should be enough for you to get the elements of it. 

http://www.cabbagepatchrailway.co.uk/mls/1140px-Buchli-Gelenkhebelantrieb.jpg 

The main driven gear is in red. The meshed levers for compensation are in white. The transfer bars are in black. The pivots for the meshed levers are fixed to the driven gear and all power is taken through them. On the driven wheel are two universal joints at the ends of the transfer bars and these move from side to side within the confines of the slot in the driven gear.... At the other ends of the transfer bars are simple pivot points that connect to the other ends of the meshed levers. 

http://www.cabbagepatchrailway.co.uk/mls/buchli1.png 

The red driven gear ALWAYS sits above the blue driven wheel in the same plane -but the centres are not co-axial. 
The meshed levers move UP allowing the wheel to sit on the rail. 
As the wheel rotates the transfer bars move across and the levers become vertical. 
The wheels rotates and the meshed levers move DOWN and the wheel remains in contact with the rail. 
As the wheel rotates the transfer bars move across in the other direction and the levers become vertical. 

So, the meshed levers are moving up and down and the transfers bars move from side to side each time the wheel and gear revolve. 

Hopefully you now have some idea of how the BBB drive system works and some idea of the type of maths involved..... 

regards 

ralph


----------



## DKRickman (Mar 25, 2008)

Okay, I have an idea of how the design works. One thing that I notice is that the bearings between the driven gear and the meshed levers are likely to wear elliptical, since they are not able to rotate though a complete turn and wear evenly. 

Two questions: 
1. Why is there a universal joint on the wheel end of the transfer bar? I would think that a simple joint would do the job. 
2. Why is the driven gear located above the wheel? Why not coaxial? I understand that the axle must move vertically, but that would seem to me easier if the "normal" position of the two were coaxial


----------



## ralphbrades (Jan 3, 2008)

Yes -there is quite noticeable wear on the pivots for the meshed levers in both of the museum pieces that I have been able to examine whilst in Berne. As to your questions... 

1: I think the reason is due to the large lateral movement of the wheel during cornering -mechanically it would make more sense to have a UJ at each end of the transfer bars. But having a simple pivot at only one end would make it easier to remove the driven gear for service (?) 

2: Yes, it would make more sense to locate the two co-axially. I have not yet found out why they are not co-axial unless it has to to do with "modes of vibration"(?) 

regards 

ralph


----------



## Semper Vaporo (Jan 2, 2008)

Speaking of "co-axialality" (is that a word?)... anyway, what supports the axis of rotation of the big gear and the wheel (if anything)?

Maybe a side drawing showing the wheel and gear as just vertical lines and whatever frame members are supporting the "axle" journals (if any) of both of them (albeit seperate and not co-axial).


----------



## ralphbrades (Jan 3, 2008)

As requested I have done a "sideways" doodle. 

http://www.cabbagepatchrailway.co.uk/mls/buchli2.png 

As before the transfer bars are in black, the driven gear in red, and the meshed levers in white. The driven gear is just supported by the frame of the loco and re-enforcing rods. The driven wheel is supported on the axle by a sprung pillow block and the other wheel with a conventional horn guide. 

Time to get back to the maths! 

regards 

ralph


----------



## Torby (Jan 2, 2008)

Mattress Wallpaper? I think you're way beyond that


----------

