Monday, 28 November 2011

Winter Project - Test track

Thinking through what I need to do to build the 57xx chassis I suddenly realised I don't have anything to test the chassis on. My test track would have been ideal if it had not been relegated to the garage (and is currently in pieces). Earlier in the year I was treated to a Bachrus rolling road and I've found this very useful in testing some of my RTR locos, though, I don't think it gives a true picture of how a loco will travel along the track. Or is this just because I like to see the locos move....?

Anyway a random length of redundant wooden shelving was retrieved from the dark recesses of the said garage (I knew it would come in useful one day), and thoughts were put towards what I might require on this strip of wood for testing locos.

1) A length of straight OO track for setting up the Bachrus rolling road and testing RTR locos prior to conversion.
2) A length of straight P4 track for setting up the Bachrus rolling road and testing locos after conversion (also for testing any chassis I manage to build during their construction).
3) A length of P4 track with a reverse curve to test a loco's abilities to travel through a minimum radius curve.

Item three above is the tricky one as what is the minimum radius curve for P4? Or possibly more importantly, what is the minimum curve for any locos I may be building? Templot shows alarm warnings at 39.4" yet the P4 Society seems to recommend not going below 48" for large locos. I guess it must come down to the length of a loco's wheelbase as to the minimum radius curve the loco can travel through. The shorter the wheelbase the tighter the curve. For the time being I cannot see myself building anything much larger than the wheel base of a WR Pannier tank. Beyond that perhaps, if my skills will allow, a 4-6-0 'N' Class and a Manor, both of which have driving wheel wheelbases similar to a Pannier tank. So I've plumped for the 39.4" radius curve as a minimum.

It's a bit rough and I will put some ends on to stop flying locos but for the moment it's located on my bench with a wall at one end and crocodile clips at the other. It may not be the most suitable test track but for now I think it should suffice.

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. 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.

Wednesday, 16 November 2011

A winter project - What to build?

Over the last couple of years I've been steadily collecting locos, RTR and kits, for my chosen period and project location. The most recent being two Dapol Beattie Well Tanks and a Perseverance Beattie Well Tank kit. For the moment though I do realise that the latter is way beyond my current capabilities as I've never constructed a loco kit.

While adding these kits to the shelf, I have been chewing the fat as to which one to build as my first attempt at a loco chassis. Ideally I thought it would be best to have started with an 0-6-0 tender loco. Starting with the tender chassis and then progress to the loco chassis. In my alternative universe I think I could twist history enough to justify running a Class 700 (Drummond's "Black Motor") - 30697 & 30700 were allocated to Exmouth Junction in 1961. I also have a BEC kit on the shelf waiting to be built. It was very tempting to make a start on this kit until it was very kindly pointed out it would take a lot of work to produce a decent looking loco from it. The tender frames are of different lengths and other castings are of dubious quality. It would also be my first white-metal loco kit and I've had little experience of constructing white-metal kits. So this kit will have to wait until I think I have enough experience.

I have also collected High Level's 03 and 57xx chassis kits. These look superb and the instructions seem second to none. However without any previous experience of building loco chassis I have found reading though the instructions daunting. Also, the thought of ruining one of these kits half way through the build is very off putting. I feel I need to cut my teeth on a kit that I could dismantle and start again, or at worst even throw away with the least worry over costs. I need to get my hands dirty with something simple.......

Thoughts turned to purchasing some Alan Gibson side frames for a DJH 1366 and/or a NuCast 16xx. I thought the 16xx kit could be a good first kit, apart from the construction of the white-metal body. Again I've had no experience of white metal kits and would like to ruin a few white-metal wagon kits before starting on the 16xx.......I could go on with many more excuses as to why most of the kits I've collected would not be good starting projects....... and you may ask why collect all these kits if I'm going to be such a chicken?

So, to cut to the chase, I've been encouraged by members of my area group to attempt to put together a Comet 57xx chassis with a Bachmann body. Compensation will be Continuous Springy Beam and the motor and gear box will be from High Level. Over the last few weeks I've been collecting all the items needed and recently purchased, off eBay, a suitably priced Bachmann body.

I do realise I am approaching this project with some naive enthusiasm but I've been receiving much encouragement and advice from members of my local P4 area group. It is invaluable having "hands on" on their locos; seeing their projects under construction; and the different techniques they have used. Having this access does much to demystify the written word in books or magazines. Hopefully I will get something running and not be too ashamed to show the result.........