34theletterbetweenB&D Posted January 30, 2017 Share Posted January 30, 2017 Preamble. Despite much RTR mechanism tinkering over the years, to date I haven't had a significant go at Heljan's products. But now the giveaway prices on the motorised parcels van make this a prime target for a plan long on the 'to do' list: to put a drive into an LNER design BG (probably a Gresley 61'6" frame type). That will require shortening the distance between bogie pivots on this mechanism, and I have an idea that might make this simple, if it is feasible. Inspecting diagrams, the way Heljan mount their traction bogies to the mechanism block is by a horizontal bar 'inboard' the bogie pivot. I cannot see any mechanical reason why the bogie pivot could not be 'turned' to lie inboard of the horizontal bar: this will effectively reduce bogie pivot spacing by twice the offset between the bogie centre and the horizontal bar. This will in turn require a shortened drive shaft and small rearrangements of the drive coupling components on the bogie gear tower to restore drive to the gear tower, and almost certainly some hacking away at the casting to provide clearance for the bogie gear tower's new position.. Question. Has anyone here successfully 'turned around' a Heljan bogie in this manner and got a reliable running result? And if so any hints and tips before I blunder ahead? Link to post Share on other sites More sharing options...
cheesysmith Posted January 31, 2017 Share Posted January 31, 2017 This reply is conditional on the fact I don't have a DPU, but I'm having trouble with picturing what you discribe. On all the other HJ stock I have (00), the bogie drive works through a bogie pivot on a bar. The bar allow fore and aft rocking. This bar where it mounts onto the bogie allows turning. This bar has a hollow centre which the CV joint is mounted at the bogie pivot centre point. The worm is just outboard of this point, and feed into the gear train in the bogie from here. They are a good simple to clip together design and placing the CV joint on the centre line of both pivot/turning makes the bogie able to move in both directions without affecting the drive. The actual driv shafts could be ignored and a motor connected to the CV joint because where it's placed. Remounting a HJ drive into something else with a different bogie spacing would actually be easy. Also, for cheap drives, look out for Clayton chassis that don't work for sale. There is ways to fix the problems they had and they also have 8ft6in bogies. Link to post Share on other sites More sharing options...
RMweb Premium Daddyman Posted January 31, 2017 RMweb Premium Share Posted January 31, 2017 Inspecting diagrams, the way Heljan mount their traction bogies to the mechanism block is by a horizontal bar 'inboard' the bogie pivot. I cannot see any mechanical reason why the bogie pivot could not be 'turned' to lie inboard of the horizontal bar: Is this what you wanted to say? I think I understand you: you're saying that the bogie pivot is not in the centre of the bogie, so by turning the bogie around, front to rear, you reduce (or possible increase) the distance between bogie centres? I don't know about this, but it maybe be possible/easier to hack the block away where it holds the bogies, and then make your own bogie mounts out of 60 thou at the position you want them. Years ago I replaced the whole chassis block in this way on a Bachmann class 25 as the chassis block was interfering with the mods I wanted to do to the solebar. But I'm not suggesting that for you - only that you replace the area of the chassis block around the bogie mount. Or not - your way may work. As to shortening the drive shafts, I did this on something I can't remember by cutting the shaft in two, removing the required amount, then putting both halves in a tube of the correct ID and correct length. This also works for lengthening shafts. Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted January 31, 2017 Author Share Posted January 31, 2017 ...I think I understand you: you're saying that the bogie pivot is not in the centre of the bogie, so by turning the bogie around, front to rear, you reduce ... the distance between bogie centres? That's it. This looks so simple and obvious that there must be someone who has tried it, surely? If not I shall just have to boldly go where the hand of man has never set foot. The great attraction is that for the application I have planned, the work will be minimal, cutting some metal from the block base for clearance of the gear tower, and the simple and proven shortening of a drive shaft using some sleeving. Link to post Share on other sites More sharing options...
cheesysmith Posted January 31, 2017 Share Posted January 31, 2017 I think you will find that the pivots are in the centre of the bogie. Turning the pivot will just make the cv joint point outwards. Shortening the distance between bogie points would be easy. Just take it to bits and saw the bogie mountings, then attach them the required distance apart. The only problem you may have is the width of the chassis casting to fit inside the body. Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted January 31, 2017 Author Share Posted January 31, 2017 The vertical pivots, the usual one we think about on bogies, do appear to be central to the bogie wheelbase or very nearly so. It's the pivotting bar in the horizontal plane that I want the vertical pivot to turn around, so that the vertical pivot then lies inboard. That will indeed leave the drive coupler pointing the wrong way, so that has to be rearranged in some way. It's quite possible that the body sides will end up 'waffer thin' to fit over the mechanism block, but I am optimistic on that aspect, as the parcels car must have had coach body exterior dimensions, and it looks the right width viewed online. Just going to have to order the item and have the fun of mangling it... Link to post Share on other sites More sharing options...
RMweb Premium Daddyman Posted January 31, 2017 RMweb Premium Share Posted January 31, 2017 The vertical pivots, the usual one we think about on bogies, do appear to be central to the bogie wheelbase or very nearly so. It's the pivotting bar in the horizontal plane that I want the vertical pivot to turn around, so that the vertical pivot then lies inboard. That will indeed leave the drive coupler pointing the wrong way, so that has to be rearranged in some way. It's quite possible that the body sides will end up 'waffer thin' to fit over the mechanism block, but I am optimistic on that aspect, as the parcels car must have had coach body exterior dimensions, and it looks the right width viewed online. Just going to have to order the item and have the fun of mangling it... Would a Bachmann 108 underframe be any better? I have one spare that I could sell you. Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted February 1, 2017 Author Share Posted February 1, 2017 Very kind, but I had already looked at the functionally identical class 105 drive, and have decided against as the wheel diameter is not readily altered to the 14mm really required for coaches. In all other respects it would have been ideal. Link to post Share on other sites More sharing options...
Silver Sidelines Posted February 1, 2017 Share Posted February 1, 2017 Hello 34C One 'disadvantage' of the Heljan 128 is that it only has one speed - dead slow. This might be an issue if you were wanting something to run at a comparable speed to other models. Ray Link to post Share on other sites More sharing options...
RMweb Gold Mick Bonwick Posted February 1, 2017 RMweb Gold Share Posted February 1, 2017 You mention 14mm wheels and probable 61' 6" underframe. As an alternative to the Heljan chassis, would a Replica Railways one be any better? http://www.replicarailways.co.uk/die-cast-chassis Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted February 1, 2017 Author Share Posted February 1, 2017 I had forgotten the Replica product, but the attractions of 'all the other bits' that come with the Heljan for even less money have swayed the decision. (I have a set of Heljan 14mm loco wheels; and a matching can size 'fast motor' for a speed upgrade if required, lurking in the spares bin from previous projects.) Now where did I store the old Kirk LNER coach kits? Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted February 3, 2017 Author Share Posted February 3, 2017 I have the device in my hands now and very good too. It was a bit of a slug at first, but an hour of running saw it achieving a scale 75mph. While exchanging the wheelsets for 14mm diameter about two thirds of the face cream goop (or whatever it is Heljan use as lube) was removed from the gear towers, and half an hour later we have a scale 112mph. So that's all very satisfactory so far. A quick look at the layout has led to a change of plan, drilling four holes makes it dead easy to resite the bogie mountings 7mm inboard both ends to achieve the 43' bogie centres of a Gresley 61'6" frame. Corresponding shortenings of the drive shafts and we are done on the mechanism, it would appear that Heljan are still using eighth of an inch as the diameter of the thickest section of the drive shaft which is convenient. (There looks to be enough clearance in the bogie openings in the frame to allow this, but I might slightly bevel the inboard edges of the openings as a little insurance.) Link to post Share on other sites More sharing options...
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