Neale
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5" Black 5 just started
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Post by Neale on Dec 13, 2018 21:53:24 GMT
I took my part-complete 5" Black 5 tender along to my local club night earlier. One piece of advice I was given was to leave one of the tender wheels to be a running fit on its axle and only lock one in place. The reason given was that curves on typical model tracks have much tighter bends than you would find if you scaled down full-size tracks and coning (if there is any) is not enough to avoid one of the wheels slipping. That is what would happen if both wheels were locked to the axle. The guy who suggested this has built a number of locos himself over the years and I am building my first, so no experience to go on. He tells me that if you try pushing a tender along with either one wheel free to turn independently or with both wheels locked to the axle, the first has much less rolling resistance on tight curves.
I have never heard this suggested before. What is the committee's view on this? Urban myth? Sound advice? Try it and see?
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Post by Deleted on Dec 13, 2018 22:07:11 GMT
Sorry but I don't care how many loco's this chap has made his advice is not sound
I understand his reasoning but disagree fully with his solution
Pete
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Neale
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Post by Neale on Dec 13, 2018 22:40:45 GMT
Seems to be one of those cases where theory and practice give different answers? I've just been doing some back-of-envelope calculations. Assume a wheel diameter of 5", track gauge 5", 30' radius bend. My arithmetic says that this would need a diameter difference between the two wheels of 0.070". Typical 3deg coning means that diameter changes by about 0.1" per inch of sideways axle movement. Given, say, a possible +-0.0625" axle float, that gives a maximum diameter difference of 2 x 0.0625 x 0.1" compared with the axle in mid-position (and assuming identical wheel diameters and coning). That is, max difference of 0.0125", nowhere near enough.
But, as the wheel gets to the limit of travel, it will also start riding on the transition curve between tread and flange, where diameter change happens much more quickly. So will the flanges hit the rails? Will the wheels self-steer as they should? Does track profile make a difference? My local club track uses rectangular steel bar as the rail, with a variable amount of wear on the corners!
And anyway, without wheels locked to axle and coning in place, how would the wheelsets self-steer along the straight? Isn't this important as well?
Maybe by the time I've reached the rolling chassis point I shall try testing the idea. Easy enough to Loctite the "free" wheel to the axle. I was just surprised that if this is such a good idea, why I've never come across it before. Still, model engineering does attract its fair share of idiosyncratic ideas! I'll have to dig back through my archived copies of ME to find those articles from way back with ideas on self-steering wheelsets for passenger trolleys - I think that that chap had strong views on wheel profiles as well.
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Post by Jock McFarlane on Dec 13, 2018 22:48:56 GMT
If one wheel is not fixed you have the additional complexity of maintaining the correct back to back gauge which is critical for running through points. Also seems pointless to do this to a tender as the black 5 driving and coupled wheels and bogie wheels will also have the same problem (or perceived problem).
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Post by suctionhose on Dec 13, 2018 22:56:30 GMT
Axle loads on a tender with no one sitting on it are very light and therefore skidding a wheel around a curve is easy. Driving or passenger cars have the heavy loads and that's where the drag will most noticeable. Even the fact your tender is 3 axles rigid is likely to produce drag from the angle of attack of the leading flanges. I once made some 12"g passenger car bogies with a free to rotate wheel. I don't know if there was a noticeable difference or not. When I went back years later they'd been replaced. I suspect the idea, even well engineered, yields little benefit. Having said that, a Sydney fellow years ago had an 0 gauge mallet that would haul the driver. I believe he had independent wheels on the driving truck and anything else that reduced the rolling friction. On 5"g - don't bother!
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Post by delaplume on Dec 13, 2018 23:12:36 GMT
Sorry but I don't care how many loco's this chap has made his advice is not sound I understand his reasoning but disagree fully with his solution Pete Yes, Pete's absolutely correct-------- and yet your man has a point!!.........So how can this be ??..........OK, let's get back to basics then}---- To save time ( and your sanity !! ) I've lifted this from our Wiki friends}--- "A vehicle with two drive wheels has the problem that when it turns a corner the drive wheels must rotate at different speeds to maintain traction. The automotive differential is designed to drive a pair of wheels while allowing them to rotate at different speeds. In vehicles without a differential, such as karts, both driving wheels are forced to rotate at the same speed, usually on a common axle driven by a simple chain-drive mechanism. When cornering, the inner wheel travels a shorter distance than the outer wheel, so without a differential either the inner wheel rotates too quickly or the outer wheel rotates too slowly, which results in difficult and unpredictable handling, damage to tires and roads, and strain on (or possible failure of) the drivetrain". In your opening post you mention that it's the Tender you have with you --- and that his suggestion would be to leave one wheel per axle to be a "Running fit" Whatever that might be ?? ....( We call ourselves "Engineers" so let's use the well-proven "System of Limits and Fits" shall we ??. ) ......OOpps...slight leak from my spleen I think !! The models built to time-proven designs already have "allowances" built in......eg}-- the back-to-back dimension and the wheel tread width...... TENDER ONLY}----- there is a design used mainly on passenger trucks where one wheel, and half the width between the 2 wheels, is made as as single unit---It looks like a wheel with a short stub on its' back....Now imagine an axle hole through the middle.......Now assemble them back-to-back onto a common axle......The axle extends through to both axleboxes but does not rotate....... Now you have 2 separate wheels on one axle which are free to rotate independant of each other ( Differential effect ) and yet will both respond simultaneously to track fluctuations...
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Post by delaplume on Dec 13, 2018 23:23:41 GMT
So what's his solution for the Locomotive then ??..........Just the requirement for 1/4-ing alone means the driving wheels must retain their relative position to one another........( What's the terminology for a 3-cylinder loco then ??-----1/3-ing ?? LoL )......
My advice ?......Smile nicely------say "Thanks" ----follow proven convention !!......QED !!
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Gary L
Elder Statesman
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Post by Gary L on Dec 14, 2018 1:41:13 GMT
So what's his solution for the Locomotive then ??..........Just the requirement for 1/4-ing alone means the driving wheels must retain their relative position to one another........( What's the terminology for a 3-cylinder loco then ??-----1/3-ing ?? LoL )...... My advice ?......Smile nicely------say "Thanks" ----follow proven convention !!......QED !! That would be my advice too, and 'proven convention' includes coned wheel tyres. We had this argument in our Club a while back, and it turned out that the people trying to reduce friction by having wheels loose on axles were also the people who didn't cone their wheels. QED! Believe me, if this dodgy idea had any (er) traction, it would have been done in full size before now. If you really want to reduce rolling friction on curves, then do it the way it is done in full-size (more or less), using self-steering wheelsets as expounded by David Hudson. This really works, but it involves radical changes in axle suspension and location, and would not be applicable to tenders. -Gary
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Lisa
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Post by Lisa on Dec 14, 2018 3:06:31 GMT
We tried this a while back; the result was that while the tread and flanges will wear with fixed wheels, with one loose you end up with worn treads, flanges, axles, and axle holes! Which makes for considerably more maintenance than just fixing both wheels to the axle, as you can't just do a quick reprofile.
However, on passenger carrying stock we ended up going with rigid axles locked to the bogie frames, with each wheel having its own roller bearing(s) and rotating around the fixed axle. This did give a significant reduction in wear.
So, if you want the wheels loose on the axle, design it that way from the beginning and use roller bearings, don't just leave a wheel loose; unless you particularly want a maintenance headache.
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Post by delaplume on Dec 14, 2018 4:37:43 GMT
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Post by delaplume on Dec 14, 2018 4:55:35 GMT
Here I have used some masking tape and Black, felt tip pen to demonstrate the two separate "half wheel+hub" idea on my own bogied driving truck..................The black line represents the 2 rubbing faces...........In my own case the 2 wheels and centre hub are all one piece with the axle protruding through at both ends into the sprung axlebox........The two axles are connected by the use of equalising beams... NB}--- The boiler in the background is for The Bear.
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uuu
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Post by uuu on Dec 14, 2018 7:40:15 GMT
An IWMES member had a 7 1/4" track round his garden. The curves were absurd, but with independent bearings on the wheels of the rolling stock it all worked well. On the club track, conventional fixed axles are entirely satisfactory.
Wilf
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stevep
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Post by stevep on Dec 14, 2018 10:28:36 GMT
I believe that if you do the mathematics, you will find that the outer rail on a 5" gauge circuit is about 18" longer than the inner one.
It doesn't matter whether the track snakes back and forth, the difference is still the same.
I have seen a solution to this perceived problem where the wheels are mounted on bearings on the axles - the axles themselves can be fixed in one of the axleboxes, as they don't rotate. (Not both, as it would interfere with the axlebox movement).
However, as has been stated, this doesn't appear to be an issue with the coupled wheels on the locomotive, so personally, I would ignore it.
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Post by delaplume on Dec 14, 2018 11:05:22 GMT
I took my part-complete 5" Black 5 tender along to my local club night earlier. One piece of advice I was given was to leave one of the tender wheels to be a running fit on its axle and only lock one in place. The reason given was that curves on typical model tracks have much tighter bends than you would find if you scaled down full-size tracks and coning (if there is any) is not enough to avoid one of the wheels slipping. That is what would happen if both wheels were locked to the axle. The guy who suggested this has built a number of locos himself over the years and I am building my first, so no experience to go on. He tells me that if you try pushing a tender along with either one wheel free to turn independently or with both wheels locked to the axle, the first has much less rolling resistance on tight curves. I have never heard this suggested before. What is the committee's view on this? Urban myth? Sound advice? Try it and see? Hi Neale' So far we have all been talking with regards to your average track set-up and operating conditions............either extruded Aluminium rail that MIGHT be tilted in the 2 degrees or so by virtue of the sleepers being machined that way...OR the use of stock steel strip laid vertical ........Either way the assembled package ( known as The Track ) is by no means "scale" at all......... There is a dedicated group who seek to build and operate 5" scale Railways in as much as an accurate a way possible ....... This is the GL5 group.. You might find their site of interest }--------- www.gl5.org/
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Post by Deleted on Dec 14, 2018 11:18:19 GMT
Just to add to the discusion a little...Would I be right in thinking this loco is a Don Young design? If so just follow the drawings..all will be fine.
Pete
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jackrae
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Post by jackrae on Dec 14, 2018 14:35:59 GMT
As an example of proof that correctly machined locked wheels are the way to go I relate the following :-
When I was a member of my local club I had difficulty understanding why our "chief" engineer insisted that free running wheels were the correct design for passenger cars Following numerous derailment problems I endeavoured to convince him that the lack of self steering was the problem and by using coned locked wheels, the problem would be resolved.
No amount of verbal persuasion was going to work so as a demonstration, I built a single axle with coned wheels. Our track was a circular loop of 660feet. I launched the axle down the track with all my might and after a few minutes it arrived back at the starting point having traversed the full track length without dropping off.
I think the point was made
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Post by delaplume on Dec 14, 2018 14:38:40 GMT
As an example of proof that correctly machined locked wheels are the way to go I relate the following :- When I was a member of my local club I had difficulty understanding why our "chief" engineer insisted that free running wheels were the correct design for passenger cars Following numerous derailment problems I endeavoured to convince him that the lack of self steering was the problem and by using coned locked wheels, the problem would be resolved. No amount of verbal persuasion was going to work so as a demonstration, I built a single axle with coned wheels. Our track was a circular loop of 660feet. I launched the axle down the track with all my might and after a few minutes it arrived back at the starting point having traversed the full track length without dropping off. I think the point was made Something like this ?? --------------> ----------> youtu.be/Mfod538CjV0
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Post by delaplume on Dec 14, 2018 15:16:02 GMT
Some of you may have seen "The Yellow Peril" out on BR track at some time or the other ??...........Its an old HST set converted for use as a Track Reconnaissance Vehicle....( TRV )....This link shows some of it's work....NB}--- I'm trying to stay within "Thread Gauge" here, OK ??....... youtu.be/n6uWJC6Yh30You may also have heard the terminology}---- "Elevation" and "Super-elevation" with respect for the approaches to, and retreat from a canted corner ??
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Neale
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5" Black 5 just started
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Post by Neale on Dec 14, 2018 17:01:25 GMT
Great to see that this thread has attracted so much attention without me needing to stir it any more!
But seriously... I have understood the principles of coning for many years. While that Youtube clip is good, what was even better for me was going to the London Science Museum and playing with their demo bit of track in the Children's Gallery. They had a straight bit of track, probably about 5" gauge, down a slope and then going into a bend. There were three wheelsets to play with. One was conventionally coned, one parallel, and one with reverse coning. No flanges on any of them. "Reverse cone" fell off halfway down the straight. "Parallel" made it to the curve and then carried on in a straight line, off the track. "Coned" followed the track with a graceful side-to-side movement.
I have to admit to an error in my sums above. I was working on the principle that the wheelset side-to-side movement was limited by axle endfloat but that forgets the little fact that the whole tender moves from side to side, therefore the diameter difference between the two wheels with the tender as far to one side as the flanges allow (and forgetting for the moment the transition fillet between tread and cone) is rather greater than I assumed. Given a tread width of just under 0.5" plus a bit of endfloat, let's say that total wheelset movement across the rails is about 0.25" from its mid position, giving a diameter difference of about 0.05". That's not quite the 0.070" needed to track a 30' radius curve, but it's not far off.
To answer some other points raised:
- I am indeed following DY's drawings, even though there is at least one serious error in the tender drawings. However, that one is nothing to do with wheel/axle fixings or wheel profile.
- DY has shown a parallel wheel tread, no coning, and I can't see mention of coning in the text. However, I have used the GL5 published standards which seem to be generally liked. Yes, I have found them! In fact, apart from details of tread profile, things like back-to-back dimensions match the DY design, which is reassuring. My local club track uses stock rectangular steel bar laid on edge in custom-moulded plastic sleepers, so with horizontal top surfaces. How much it's worn over the years I don't know.
- Most of this argument has been dealing with behaviour and performance on curves. Is there actually a compromise needed between what gives lowest rolling resistance on curves and what self-steers, keeping flanges away from rails, on the straight? Coning and solid axle would be best on straights, but suffering from slightly higher rolling resistance due to need for one wheel slipping on curves?
- As someone with no preconceived views here, I am picking up suggestions that both techniques are best! We have people who use free-running wheels, and others that have "proved" that solid axles/coned wheels work best. Is there a difference between passenger car bogie use and rigid-body tender use? My leaning is towards traditional coned wheel/solid axle, backed up by rough calculations that say (and contrary to what my mate at the club was saying) that there is enough coning in model size and on typical club tracks to get a useful amount of self-steering, hence lower overall rolling resistance and less chance of derailing.
- I alternate between "scientist" - gimme theory and calculations! - and "engineer" - just make the b****y thing work! However, it's great when practice is backed up by theory as this can give us more insight which can lead to improved design, and when theory and practice don't match - which is right? What is it that we don't properly understand? AFter all, for centuries everyone "knew" that heavy objects fell faster than light objects... Hence arguments based on an implied "everyone knows that..." are fun to read but don't really carry much weight.
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Post by 92220 on Dec 14, 2018 17:45:58 GMT
I took my part-complete 5" Black 5 tender along to my local club night earlier. One piece of advice I was given was to leave one of the tender wheels to be a running fit on its axle and only lock one in place. The reason given was that curves on typical model tracks have much tighter bends than you would find if you scaled down full-size tracks and coning (if there is any) is not enough to avoid one of the wheels slipping. That is what would happen if both wheels were locked to the axle. The guy who suggested this has built a number of locos himself over the years and I am building my first, so no experience to go on. He tells me that if you try pushing a tender along with either one wheel free to turn independently or with both wheels locked to the axle, the first has much less rolling resistance on tight curves. I have never heard this suggested before. What is the committee's view on this? Urban myth? Sound advice? Try it and see? The simple answer is that if it is necessary on a tender to have one wheel loose on the axle, then the same reasoning must also apply to the loco! Oops! NOT exactly a good idea!!! Bob.
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