Monday, 21 November 2011

A winter project - Getting to grips with CSB

Understanding the principles of Continuous Springy Beam and using the spreadsheets have been the first steps of this project. In principle it all makes good sense, but the maths and the theory do get very confusing for a lesser mortal like myself. However, the spreadsheets are the tools that turn all the theory into usable figures.

Unfortunately the first spreadsheet I downloaded caused me some confusion. It was one of Will Litchfield's and with hindsight my confusion was mainly due to me not knowing what I was trying to achieve. If only I'd realised what I would be doing now I would have tried to attend Will's lecture on CSB and John Brighton's on Chassis Building at Scaleforum ...... Anyway, at first sight Alan Turner's spreadsheet seemed to make more sense to me. The only drawback that I could see with Alan's offering is how can I calculate the centre of gravity of a model that I haven't yet built? But.... working on the principle that, if I put the centre of gravity roughly around the centre axle and weight all axles as near the same as the spreadsheet will allow, I can add weight to the finished model to move the centre of gravity over the centre axle.

After a little fiddling around I ended up with the calculations below. This was using Alan Turner's spreadsheet, for a 57xx chassis.
Once I'd started to use the above spreadsheet some of the theory started to sink in. I'd also been pointed in the direction of a different spreadsheet produced by Will which was not as daunting as the first. After some further discussions with group members, and a few more reads about CSB on CLAG's web pages, I was gaining a better understanding of the principles. Especially about the reasons for reducing the weight of the centre axle. Which, if my understanding is correct, is to help with: keeping the loco level; to enhance traction/grip; and reduce/avoid waddling ('porpoising') of the loco as it progresses along the track. I'm starting to feel I as if I'm getting to grips with CSB.....

The same figures entered into Will's spreadsheet seem to confirm that I might be on the right track.....


Considerations I have tried to take into account while using the spreadsheets to calculate fulcrum positions are: position of brake hangers; position of frame spacers to avoid the CSB mounts and wire; position of the frame spacers which will be used to mount the wire pick-ups; the position of motor and gear box. The diagram below hopefully shows my thoughts......


The only bit that I'm still trying to work out is how to support the motor/gearbox.... One idea (marked in green on the above diagram) is to solder some wire to the inside of both frames around the centre axle and bend them in and under to support the motor. Then either solder them to each side of the gear box, or drill a hole in the gear box for the wires to pass through supporting the gear box but not fixed permanently. The wire supports would be like a cradle for the motor to rest on and secure the gear box vertically. Would there be enough play in the articulated part of the gear box to allow suspension on the rear axle? The wire forming the cradle might not give a solid support but one that might have some flexibility allowing the gearbox some slight vertical movement. But....is there a better method?

I don't see that not knowing how to support the motor/gear box should stop me from installing the handrail knobs (that will be used as the CSB fulcrum points). So, I'm hoping to get started on construction during the next few evenings while I'm thinking/asking questions about the support for the motor/gear box.

3 comments:

Flymo said...

I'd follow your idea, but rather than put the wires from the frames into or onto the gearbox, I'd bend them to form a cradle for the motor to sit on.

If you've seen the pictures of my Tram Engine chassis, you'll see that the motor just rests on top of a plasticard plate across the frames. this seems to work perfectly well :-)

Russ said...

There would be enough play in the articulated part of the gear box to allow suspension on the rear axle, but it's not a good idea - the torque from the gears will lever the driven axle up or down, depending on the motor direction, thereby altering your intended spring pressure. For a sprung axle, the consensus is that any loose swing arm on a HL box needs to be made solid with the gearbox.

The motor will need to be supported somewhere, and the best way of doing this is with a torque reaction link. Some ideas are here.

Yan said...

Thanks Russ

I had been informed that the best option is to fix the articulated part of the gearbox. BUT I was still not sure why, as it made more sense to me to leave it loose. However your description has explained all...

Thanks again and thanks for the links