Coach bogie Posted February 13, 2011 Share Posted February 13, 2011 Compensation etc is another arguement entirely. Personally, at the risk of bringing controversy in and upsetting some people, I feel the extra complication isn't worth the grief. The only locos I have builtor for others that have any benefit in using compensation are the short wheel base four couples such as the 14xx and all the industrials. I ensure the chassis is running perfectly and I have never had any issues with poor pick up etc, ( I also have a similar approach to track laying). I was lucky enough to visit Roy Jackson's Retford for a fantastic Sunday recently. EM, kit/scratchbuilt locos, no compensation/suspension - no stuttering, no finger pushing - just total running perfection. Compensation couldn't possible contribute anything here, and I wouldn't dare suggest so to Mr Jackson without a paramedic present. Again PERSONAL opionion, but in my case, it all works. Mike Wiltshire Link to post Share on other sites More sharing options...
jamieb Posted February 14, 2011 Author Share Posted February 14, 2011 I've never really considered how fitting a body to a chassis could alter the running characteristics and would normally go for a pretty rigid fit, but there's some food for thought here.If a rigid body is firmly attached to a rigid chassis, then I assume any inaccuracies on either would have an overall magnifying effect on the rigidity of the whole.Similarly, a loosely fitted body on a compensated chassis would have the potential to be a sloppy mess.Knowing how and where to strike the balance would seem to be the key to successful running. Would a rigidly fixed body work better with sprung hornblocks where any inaccuracies are absorbed simply by a spring rather than sending shockwaves through the whole chassis which seems to be a feature (albeit exaggerated!) of compensation- and is the apparent lurching of some compensated chassis more an observation of a rigidly fixed body jerking about, rather than a weakness in the chassis. I know over the years there has been a lot written about compensation vs springing , with it seems springing having won out in the end , now CSB's are becoming a viable option which seems to be an amalgam of the two systems. Getting back to my own case, I don't see a need on the 4 coupled wheels for any compensation, providing the front carrying wheels have some form of springing to maintain track contact and thus electrical contact .If I replace the boiler with copper pipe it should add some weight to the body - providing the rest of the etched superstructure is strong enough to support the weight.This I won't know until I start to build it but already plan to reinforce the footplate and possibly inside the side tanks.As for fixing the body, maybe screw and bolt at chimney end and a small pad of velcro(!!) under the cab.Any comments or am I mad to consider it? Jamie Link to post Share on other sites More sharing options...
hayfield Posted February 14, 2011 Share Posted February 14, 2011 Jamie Iain Rice advocates that only one end is screwed to the body, the other end should just clip in place. Also some form of rubber or sponge sheet between the body and chassis. From memory this to stop vibration to reduce noise and give better running as there is less vibration. I must remenber not to tighten the screws too much Link to post Share on other sites More sharing options...
Jol Wilkinson Posted February 15, 2011 Share Posted February 15, 2011 I've never really considered how fitting a body to a chassis could alter the running characteristics and would normally go for a pretty rigid fit, but there's some food for thought here.If a rigid body is firmly attached to a rigid chassis, then I assume any inaccuracies on either would have an overall magnifying effect on the rigidity of the whole.Similarly, a loosely fitted body on a compensated chassis would have the potential to be a sloppy mess.Knowing how and where to strike the balance would seem to be the key to successful running. Would a rigidly fixed body work better with sprung hornblocks where any inaccuracies are absorbed simply by a spring rather than sending shockwaves through the whole chassis which seems to be a feature (albeit exaggerated!) of compensation- and is the apparent lurching of some compensated chassis more an observation of a rigidly fixed body jerking about, rather than a weakness in the chassis. I know over the years there has been a lot written about compensation vs springing , with it seems springing having won out in the end , now CSB's are becoming a viable option which seems to be an amalgam of the two systems. Getting back to my own case, I don't see a need on the 4 coupled wheels for any compensation, providing the front carrying wheels have some form of springing to maintain track contact and thus electrical contact .If I replace the boiler with copper pipe it should add some weight to the body - providing the rest of the etched superstructure is strong enough to support the weight.This I won't know until I start to build it but already plan to reinforce the footplate and possibly inside the side tanks.As for fixing the body, maybe screw and bolt at chimney end and a small pad of velcro(!!) under the cab.Any comments or am I mad to consider it? Jamie Jamie, getting a chassis to run well in isolation and then bolting it to a more rigid structure (which is invariably the case) can lead to distortion of the chassis with an adverse affect on running. In fact it's more likely to affect a rigid chassis as the "flexibility" built into compensated/sprung/CSB's chassis will cope to some degree. That's probably one reason I find it easier to get P4 locos running far better than I ever did with 00 models. "Lurching" of a compensated chassis is down to poor trackwork. The reaction of the "fixed" axle - usually at the end of the coupled set - when passing over vertically misaligned rail joints is what causes the whole loco to lurch. While springing and CSBs have certain advantages, compensation is still a straightforward approach to provide better traction and pickup, especially on well built track. I have two compensated four coupled locos, with pickups only on the coupled axles. They run very well under exhibition conditions at lowish speeds on an end to end layout. To have fitted pickups to the carrying wheels would be difficult but compensation (or springing) obviates the need. That's not to say that more pickup points aren't a good idea, it's not always practical. In another posting, Mick Wiltshire referred to the running of Roy Jacksons EM locos on Retford. Having briefly operated Retford on one occassion I can agree entirely, but I would suggest that large, heavy locos running at reasonable speed and on layouts where longer runs are possible will operate rather differently to smaller and lighter (in my case) locos at lower speeds for brief periods of time. The same possibly applies to other large layouts, such as Stoke Bank, The Gresley Beat, etc. IIRC Chris Pendlenton found that springing and large flywheel drives were a great assett to the large locos on his layout, which is another of the "short run" type. Perhaps it's a matter of horses for courses. Link to post Share on other sites More sharing options...
Kenton Posted February 15, 2011 Share Posted February 15, 2011 In fact it's more likely to affect a rigid chassis as the "flexibility" built into compensated/sprung/CSB's chassis will cope to some degree. I am not sure I can agree with that. In an ideal world and from the engineering point of view it may well be true. However in the case of starting with weak and flexible frames, cutting massive chunks out of them to introduce a moving component such as a hornblock that provides no further strength to the frame can only result in more flexability of the frame, possibly in directions that would otherwise be sound. The inverted U shaped frame or H cross-section are already compromised. Start out with thin material cut into it at its weakest/narrowest point and add flat frame spacers of equally flexable and thin material and you get a wobbly result that no springing can cope with. It would be nice to have the rigidity of a say a Finney chassis where the the addition of hornblocks have been designed into the structure but this is a FB chassis and one of the smallest ones to be built. Link to post Share on other sites More sharing options...
Jol Wilkinson Posted February 15, 2011 Share Posted February 15, 2011 I am not sure I can agree with that. In an ideal world and from the engineering point of view it may well be true. However in the case of starting with weak and flexible frames, cutting massive chunks out of them to introduce a moving component such as a hornblock that provides no further strength to the frame can only result in more flexability of the frame, possibly in directions that would otherwise be sound. The inverted U shaped frame or H cross-section are already compromised. Start out with thin material cut into it at its weakest/narrowest point and add flat frame spacers of equally flexable and thin material and you get a wobbly result that no springing can cope with. It would be nice to have the rigidity of a say a Finney chassis where the the addition of hornblocks have been designed into the structure but this is a FB chassis and one of the smallest ones to be built. Kenton, the point I was trying to make was that adding a twist to the frames would be counteracted by the axle bearing moving in the hornguide. With a rigid chassis the axles would become misaligned - so all that careful setting up on a flat plate would be ruined. I think that it depends on the frame and hornblock/guide designs. A big long chassis with three spacers won't have any more torsional stiffness than a small short one with three spacers. Most manufacturers use .015" n/s which is much more robust than .012" brass which is what I think you get in a Jidenco kit. The LRM cast brass hornguide for example is pretty solid (much more than any of the etched brass ones I have used) and will stiffen the frames around the axle cut-out area, but may be too big for the small frames on a loco like a Terrier. This may be a good example of the original kit being unsuitable as a decent starting point without replacing the frames, etc. (Alan Gibson lists a set of Terrier milled frames). The only Jidenco loco I ever attempted was the LNWR 0-8-2T. I gave it up because the cab was inaccurate, the chassis flimsy and my skills at the time werene't sufficiently well developed to cope with it. Further the prototype wasn't really one I needed for the layout so it became a No Go. I've had a go at other Jidenco wagon kits and wouldn't ever bother with one again unless I was completely convinced that FB had completely redesigned it. Jol Link to post Share on other sites More sharing options...
Horsetan Posted February 15, 2011 Share Posted February 15, 2011 Why doesn't someone build a loco in 18.83mm gauge, with a rigid chassis, and then have it tested on as many layouts as possible? Most P4-rewheeled RTR diesels, and not a few RTR steam ones are pretty much rigid-framed, and we don't hear many stories of these consistently derailing or otherwise having traction problems, so we will all be able to see whether a steam-outline kitbuilt one will perform in similar manner. Link to post Share on other sites More sharing options...
halfwit Posted February 15, 2011 Share Posted February 15, 2011 Why doesn't someone build a loco in 18.83mm gauge, with a rigid chassis, and then have it tested on as many layouts as possible? Along with an identical loco - same weight, same drivetrain - built with CSB? Link to post Share on other sites More sharing options...
Kenton Posted February 15, 2011 Share Posted February 15, 2011 Why doesn't someone build a loco in 18.83mm gauge, with a rigid chassis, and then have it tested on as many layouts as possible? Probably because they will be ridiculed and mobbed into a quivering puddle long before they were allowed to get it near a layout. It often seems to me that to claim to model P4 you MUST spring your chassis as a requirement of wearing the label. Though this debate is not really relevant to this particular kit and the OP is not proposing to build it to P4 Link to post Share on other sites More sharing options...
jamieb Posted February 15, 2011 Author Share Posted February 15, 2011 Why doesn't someone build a loco in 18.83mm gauge, with a rigid chassis, and then have it tested on as many layouts as possible? As I've always understood it, the main point of incorporating some form of suspension in P4 is to keep the tiny flanges running over any track irregularities.A big heavy whitemetal loco on Retford for example would probably manage quite nicely without but for most of us running our locos at a scale 5mph (because we can!)need as much help with the track holding and hence electrical pickup as possible.Anyone could probably replace OO wheels with P4 and run it down a yard of flexitrack with no ill effects but once curves , turnouts and track joints come into play, we'll be off the rails.After all, the full size versions needed springs and look how much weight they carried.(I don't think Sir Nigel designed the A4 with streamlining so he could fit a piece of lead sheet inside it to help the traction.) Drop-in wheelsets such as Ultrascale provide for RTR depend upon the inherent sloppiness of proprietary chassis.Hand made or kit built chassis seem to depend on tighter tolerances, so are we making a rod for our own backs?But we are using lightweight brass or N/S frames as opposed to heavy mazak ,or similar ,castings from the RTR boys, which brings us back to the weight issue.As Kenton points out though,I am not intending to build to P4 standards.My aim is to produce a running loco with as little extra expenditure as possible.So no replacement Gibson frames etc, I intend to use as much of the kit as possible ,even though I've got a Branchlines chassis in the TO DO box.I'm not mad , just tight! After all £12 could easily become £50 or more but that defeats the original idea. Jamie Link to post Share on other sites More sharing options...
jamieb Posted February 20, 2011 Author Share Posted February 20, 2011 See thread here for the aforementioned Cambrian Brake Van http://www.rmweb.co.uk/community/index.php/topic/31884-cambrian-brake-van/page__view__findpost__p__335127__fromsearch__1 Link to post Share on other sites More sharing options...
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