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Old May 13th, 2010, 10:02 PM   #121
Frank H
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Many thanks to Tramfreak, historyworks, and Sch1 for their enlightening replies to my last post.

Thanks to Sch1, I now know more about the competing advantages and disadvantages of synchronous and asynchronous AC electric motors. I can see why Skoda chose synchronous motors for the 15T. The fact that Skoda uses asynchronous motors in its other designs, as do, if my impression is correct, most if not all other modern tram manufacturers in their designs, prompts the question "why?"

I presume that Sch1 has pointed out the answer in the statement "the drive train is more expensive." I presume that this also means that it is more complex.

This might mean that the drive train is the potential "weak link" in this design. It will be interesting to see how it holds up in regular service.
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Old May 14th, 2010, 07:14 PM   #122
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Quote:
Originally Posted by Sch1 View Post
Hi Frank H,
I will try to explain the reasons which may have led Škoda to use synchronous motors in 15T.

The size enables to connect the motor directly to the wheel and save additional weight and space by avoiding a gear box. Prague requested the least track wear possible.

The disadvantage is that is more difficult to use in in traction vehicles since the voltage in the overhead line fluctuates. Thus the drive train is more expensive.

Lower maintenance costs are for sure due to the absence of the gearbox. Higher efficiency is achieved because the synchronous motor has better electrical efficiency and there are no losses in the absent gearbox, so this is a combination of the parameters of synchronous motor and the gearlessness of the drive train.
Reading through this again, I realise I may have misunderstood the situation.

I presume now that ..."the drive train is more expensive" does not refer to the same part of the mechanism as is referred to in "...the gearlessness of the drive train". i.e. there are two different drive trains.

I would have taken "drive train" to mean the link between the motor and the wheels. It appears that this is a very simple arrangement in the 15T - with the motors, because of their small size, being able to drive the wheels directly. Thus I presume that this is not the "more expensive" drive train apparently required by a synchronous motor. Would that refer to the connection between the pantograph and the motors?
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Old May 15th, 2010, 12:46 AM   #123
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Quote:
Originally Posted by Frank H View Post
Reading through this again, I realise I may have misunderstood the situation.

I presume now that ..."the drive train is more expensive" does not refer to the same part of the mechanism as is referred to in "...the gearlessness of the drive train". i.e. there are two different drive trains.

I would have taken "drive train" to mean the link between the motor and the wheels. It appears that this is a very simple arrangement in the 15T - with the motors, because of their small size, being able to drive the wheels directly. Thus I presume that this is not the "more expensive" drive train apparently required by a synchronous motor. Would that refer to the connection between the pantograph and the motors?
I am out of my depth on some of it too Frank H - all I know is that Skoda is obviously a very clever designer and manufacturer of transport electrics so they seem to know what they're doing. I think even Bombardier is using some of their electronics. Skoda seems to be focussing on transport now, having sold Skoda Power to Korea. Apart from their own decades of experience I believe Skoda inherited much of the technical staff and research facilities of CKD Tatra so there is a lot of tram knowledge and experience there. Perhaps some of our Czech friends can help fill in the details.
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Old May 17th, 2010, 11:41 AM   #124
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What I meant with drive train was everything from the pantograph to the wheels, the mechanics are simpler, thus require less money to build and to maintain, but the electronics that feed the motors with energy are much more complex, thus more expensive to build.
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Old May 17th, 2010, 10:06 PM   #125
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Originally Posted by Sch1 View Post
What I meant with drive train was everything from the pantograph to the wheels, the mechanics are simpler, thus require less money to build and to maintain, but the electronics that feed the motors with energy are much more complex, thus more expensive to build.
Thanks Sch1. Your two posts have given me more appreciation of the differences between - and the qualities of - asynchronous and synchronous AC motors than anything else I have found on the web. Items found there are either too basic - telling me nothing I didn't know already - or far too advanced - my knowledge of electric motors is limited.

Regarding the 15T, the arrangement of the motors directly driving on the wheel makes the bogie look quite strange.

http://webak.upce.cz/~lata/konferenc...gr_heptner.pdf

This document has pictures of many modern tram bogies. Obr. 20 shows that of the 15T. I presume that the bulky round objects situated on the outer ends of the axles are the motors.

Another view of this comes from the Riga tram thread, page 2, in post 23 from Hybrid 87:
http://www.skyscrapercity.com/showth...1061263&page=2

Of course, in service this will be hidden by the bogie cover. A close look at this from Wikipedia seems to show the way the motor fits into this:
http://en.wikipedia.org/wiki/File:%C...t_podvozku.jpg

It must be a pretty tight fit. The fact that this rather awkward looking arrangement seems to be working OK is another triumph for Skoda - but perhaps such a peculiar arrangement has been used before - does anyone know whether this is so?

Anyway, tram enthusiasts will be waiting with interest to see how the remarkable 15T performs in everyday service.

I express again my regret that we will probably never see the 15T in action in the UK. Or the Solaris Tramino for that matter.

Last edited by Frank H; May 18th, 2010 at 12:07 AM.
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Old May 18th, 2010, 01:48 AM   #126
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Frank H I think hub motors are quite common on low floor trams, I don't think that aspect is unusual. In fact I think you can see them on several examples in that pdf article you linked (great bit of googling to find that Frank!).

I would love to see English translation of that article (without the oddities of Google Translate and its "80% low floor sex" as they found on the Riga forum LOL!). There is very advanced stuff on trams coming out of Czech Republic that we have no congniscance of in the old "west" - but after all they were the world's largest tram builders for the last half-century, they do know a lot more than us.

I don't know why in theory you shouldn't see 15T in UK (same in Australia). The "western" countries have no understanding of anything east of the Elbe let alone how sophisticated it might be. The big manufacturers have their market turfs and nobody goes outside the square. Also loss of knowledge of tram operation in the new-start light rail countries means they have no critical tradition or engineering experience on which to evaluate a tram. It is easier to give the start-up job to a package "turn-key" consortium with "any-tram-will-do" included (ineveitably a Bombardier or Alstom). I think this approach will bite them on the bum one day when the limitations of the fixed bogie trams become obvious (already on the 13 year-old Sydney light rail line, which has fixed-bogie Variotrams, there is discussion of premature track-wear).

Personally I think Skoda should be linking up with some of these turn-key consortiums when tendering for contracts in the "west" (except the less-prejudiced USA where Skoda and Inekon are doing quite well in establishing a profile). It all comes down to marketing/sales skill in the end.

By the way, note in the Riga photo of the 15T on the transporter how the Riga version does not have motors on the first bogie (in Prague 15T has all bogies powered). I presume this is because Riga is reasonably flat, without the steep grades that are prevalent in Prague. Also interesting because unpowered bogies are usually further back on trams (with the sanders on the front wheels). Perhaps Skoda has worked out that traction in slippery conditions is better with the powered bogies further back - better weight distribution? Clever Czechs LOL?!
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Old May 18th, 2010, 02:38 AM   #127
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Ah what the heck! Here's a Google translate version of that article (carefully screened for references to 80% low floor sex!). I think - as we say in English Frank - we have to "read between the lines" to understand, I hope some of our Czech friends can help to clear up some of the meanings.

Basically it seems to be a discussion of efforts to return to a more "classical" form of tram running gear, of which Skoda has made it all the way. You will note that Alstom has also brought out a pivoting bogie, but only for use under the ends of the tram and without revisiting the whole architecture of the tram as Skoda has (which is a pity I think - a half-hearted effort).

Quote:

Original Czech: http://webak.upce.cz/~lata/konferenc...gr_heptner.pdf

Rotary CHASSIS Articulated trams
Milos Zelingr, Tomas Heptner

1 INTRODUCTION
Tram car went through a period of its existence in many forms. Latest development
group are low-floor trams. This paper describes the relation between concepts and the vehicle chassis, and it with an emphasis on return to the revolving truck assemblies.

2 What is SWIVEL TO LANDING GEAR
Streetcar in the current implementation is usually vícečlánkové vehicle stored on several chassis. One feature of the chassis, which we will specifically deal with its
otočnost to the vehicle body about a vertical axis. If we wanted to find a definition of the chassis, or directly to the chassis pivot, we insight into the script such as Prof. Nejepsy "wagon I" (SNTL Prague, 1953) [1]. Here is chassis is defined as follows: "The chassis is a low chair for two or more wheelsets, with a wheelbase of 1.8 to
3 mi more bearing housing such a way that can shoot around it about a vertical axis. "In same publication is exemplified by the term "non-slewing chassis - Figure 1
Fig. A script "Doc. Nejepsa: wagon I "- illustration neotočného chassis

3 LANDING GEAR as a key component low-floor trams
Low-floor trams are usually more of its floor located at a height of approximately 350 mm above rail (BP), then at the height axis of the axle of classic cars PCC concept, in our represented by type T3. In the space above the floor of the chassis frequently located at slightly increased. For 100% low floor tram vehicles are considered the height above the floor * / Ing. Zelingr Milos, Ing. Tomas Heptner, VÚKV a.s. Prague
80 Current problems in rail vehicles in 2009 trucks up to 450 mm above TK, the transition between different levels of the floor realized by means of ramps.
If such a reduction has been achieved over the floor and chassis, it is clear that the chassis had to undergo a fundamental transformation. The key to this was mainly the removal of the axle from its normal positions, respectively. its replacement by other means storage rental.

3.1 Swivel common chassis with wheels of small diameter
One option for the floor area of the release was to use small diameter wheels. This solution was used for conventional chassis in the 80 and 90 years - it was such a tram Be 4 / 8 (Vevey) or NGT 8D (Alstom LHB - Figure 2, 3), where the two common chassis with wheels diameter 410 mm placed under a low-floor middle article.
Fig. 2 Tram NGT 8D - Alstom-LHB
Fig. 3 normal chassis Alstom-LHB

3.2 non-slewing chassis
Normal chassis with wheels, small diameter leading through minimizing their building height the relatively large space restrictions for passengers. Low-pass-through lane of the chassis was wide, only around 500 mm and a seat on its sides had to be placed on the landings. This could be disadvantages associated with using a small diameter wheel substantial reason chassis for use neotočných or partially rotating (rotatable chassis to the rack. As defined angle stops and chassis to the cabinet is limited to about 1 ÷ 5 °). Vehicles these trucks are the vast majority of low-floor tram produced in the last twenty years. If the designers were trying to use wheels with a diameter of 600 mm, it was clear that trajectory rotating wheel bogie would constitute a substantial limitation of the width of the passage and therefore and restrictions on the movement of passenger vehicles - Figure 4 Likewise, the use of remedies with its axis at a height of approximately 300 mm above T.K. for low-floor tram was unacceptable. It was therefore necessary to look for other solutions.
Current problems in rail vehicles 2009 1981
Like an optimal storage proved independently rotating wheels to break welded or
forged beam - axle (Fig. 5) or the imposition of separate rounds of swinging arms.
Fig. 4 Limitations of the passenger compartment and a rotary gear neotočným
Fig. 5 axle - Bochumer Verein
Axle was used in a chassis neotočných placed under either a short-medium Article tříčlánkové trams (with front and rear part of a low-floor article navěšeným
Article on Central - Figure 6), under each of such articles tříčlánkové trams (Fig. 7) or under every odd (first, third, fifth, ...) Article vícečlánkové tram-wheel with odd and
the even borne cells (Fig. 8).
Fig. Tram 6 TSF2 - Alstom
Fig. 7 Tram GT6N - Bombardier-Adtranz
82 Current problems in rail vehicles in 2009
Examples of this approach tram bogies are in Figure 9 and 10 - chassis Siemens
the axle and chassis-Adtranz Bombardier with swinging arms.
Fig. 8 "Family" Combino tram
Fig. 9 Operator and chassis Combine - Siemens
Fig. 1910 Chassis FLEXIT Outlook trams (Eurotram) - Bombardier.
The concept is linked chassis and drive solutions - such as engine and longitudinal (front-) bevel gearboxes, moving the two wheels "behind", or an individual drive with transverse Stored engine and front gearbox (or by charge to the engine and the planetary gear) in the swingarm.
Current problems in rail vehicles 2009 1983
Fig. 1911 Chassis trams Variobahn - Bombardier

3.3 Other solutions
The design of low-floor trams, there were other concept vehicles and their travels
(Portal, two-wheeled travel ULF - Siemens, a four-wheel travel Cobra - Bombardier and others), in Compared with the above but did not receive wider application.

4 Return to the rotary truck assemblies
The use of low-floor tram bogies with neotočnými begun to show Worse, some features of this concept vehicle. It is about guiding the tip forces during a raid
the arc, where (depending on the routing line on the state of track surfaces and the adaptation technology driving the concept car) on a small basis Locations forces that provide housing rotation Article bogie about a vertical axis, pose different power relationships than with rotating tram chassis - Figure 12th
Fig. 12 boxes and moment of inertia forces between wheels and rail
Despite the apparent economic success of the sale of vehicles and chassis neotočnými
there are returns of some older concepts of the chassis as the development of new concepts.
Fig. 1913 Tram FLEXIT Classic - Bombardier
Under low-floor trams cells appeared normal swivel wheeled chassis normal
diameter (Bombardier - Figure 13, 14). The articulated trams with articles have been borne under customs modules, which are the guiding forces of the most problematic aspects, re-used rotary current chassis with small diameter wheels (Alstom, Siemens - Figure 15, 16).
Fig. 14 Standard tram chassis FLEXIT Classic - Bombardier
Fig. NF 15 Tram 8 - Siemens
Fig. 16 Standard tram chassis NF 8 - Siemens
Current problems in rail vehicles 2009 1985
In particular the existence of full-fledged conventional rotary chassis idea that the appropriate choice of power projection will shortly be low-floor vehicles with rotary drive chassis. Currently, two solutions are known for such vehicles is conceptually distinguished. Tram Citadis X series (Fig. 17) has one rotating chassis under extreme articles and two
swivel bogies under Article medium. Chassis (Fig. 18) have two synchronous motors, which through customs and bevel gear drive, each one "wheelset - a pair of wheels
imposed on one axle, the shaft coupling between the two wheels.
Fig. Tram 17 Citadis X Series - Alstom
Fig. 1918 Chassis iXége trams Citadis X Series - Alstom
Škoda 15 T tram ForCity (Fig. 19) has two modules under the front chassis with an eccentrically located otočovým bearing and two bogies Jakobs the joints (Fig. 20) - for each such the chassis via two bearings otočových saved two adjacent cells trams.
Propulsion wheels are available individually, by synchronous motors without gearbox, with only short connecting shaft.
Both these vehicles have a floor at a height of 350 mm above TOR in the space above the chassis increased through the ramp.
86 Current problems in rail vehicles in 2009
Fig. 19 Streetcar 15 T ForCity SKODA - SKODA
Fig. 1920 Bogie tram Škoda 15 T ForCity - SKODA

5 Conclusions
The trends in low-floor trams is clear that these vehicles are looking for ways
to return to classical structures. Rotating chassis is one of the basic structural units of classic tram and it seems that will still apply even more modern low-floor trams.
Thanks

This post has been supported by the Ministry of Education project 1M0519 - Research Center Rolling
vehicles.

Literature
1st NEJEPSA wagon R. I SNTL, Prague (1953).
2nd Brochure Bochumer Verein
3rd Brochures tram Adtranz, Alstom, Bombardier, Siemens, Skoda
4th H. Hondius ÖPNV-Niederflur-Fahrzeug im kommen, Stadtverkehr, 2 / 1998
5th Hondius H. Die Entwicklung der Niederflur Mittelflur-und Strassen-und Stadtbahnen -
Folge 12 ÷ 23

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Old May 18th, 2010, 09:04 PM   #128
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Quote:
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Frank H I think hub motors are quite common on low floor trams, I don't think that aspect is unusual. In fact I think you can see them on several examples in that pdf article you linked (great bit of googling to find that Frank!).
Thanks for your comments. I had heard of hub motors on trams before, but assumed that they were a special case only used on a few tram types.

If indeed hub motors are common on low floor trams, I am rather puzzled when looking at the pictures of bogies in Zelingr & Heptner's paper. My puzzlement comes because of what I learnt from Sc1 in this forum thread - that synchronous motors - as in the 15T - are smaller and lighter than asynchronous motors (I assume that this of course must be in comparing motors of similar power output).

Looking at the pictures in Z & H, it seems to me that, while all the bogies show equipment on the outer end of the axles, outside the wheels, that of the Skoda 15T (Obr.20) seems the largest and bulkiest. Only that of the "Variobahn - Bombardier" (Obr.11) comes close to this. I had wondered whether this tram might also have hub-motors. The outside-of-axle equipment on all the other bogies seems much less than that on the two above-mentioned designs - and much of the equipment doesn't look particularly motor-like to me, but then I have very limited knowledge in this field. That of the Siemens NF 8 (Obr.16) has what look to me possibly motors, not directly on the hub but above and to one side, presumably driving the axles through gears. (And see below on the Citadis X Obr.18)

Thus if motors are present in the pictures of these bogies, they all seem to be smaller and lighter than the synchronous motors of the 15T. But it was my understanding - possibly mistaken - that most modern trams had asynchronous motors, which accordingly ought to be larger than the 15T's motors.

Quote:
I would love to see English translation of that article (without the oddities of Google Translate and its "80% low floor sex" as they found on the Riga forum LOL!).
Thanks for the Google translation of Z&H. Sadly this confirms that Google translation is, as might be expected, at its worst when attempting technology and science. I'm afraid I find it almost impossible to understand much of the resulting gibberish. However one important piece of info. does emerge - that the Citadis X trams do have synchronous motors. They can be seen in Obr. 18 on the outside of the bogies - but not hub-mounted - each motor driving both axles through shafts coupling to bevel gears. It is probably significant that, as you pointed out, this tram by Alstom also uses a pivoting bogie, but in a different way (aptly described by yourself as "half-hearted") to Skoda's 15T bogie.

Quote:
There is very advanced stuff on trams coming out of Czech Republic that we have no congniscance of in the old "west" - but after all they were the world's largest tram builders for the last half-century, they do know a lot more than us.

I don't know why in theory you shouldn't see 15T in UK (same in Australia). The "western" countries have no understanding of anything east of the Elbe let alone how sophisticated it might be. The big manufacturers have their market turfs and nobody goes outside the square. Also loss of knowledge of tram operation in the new-start light rail countries means they have no critical tradition or engineering experience on which to evaluate a tram. It is easier to give the start-up job to a package "turn-key" consortium with "any-tram-will-do" included (ineveitably a Bombardier or Alstom).
That's the root of the problem. Despite perfunctory nods in the direction of free and fair trade, protectionism and narrow economic nationalism seem to be far from dead in the western world.

Tha "Anglo-Saxon" countries - USA, UK, Australia etc. - are actually among the least protectionist. Hence, probably, the comparative success of Eastern European and Asian companies in these countries. However in the UK and Australia - after privatization - many of the leading providers of public transport are in foreign hands. If, as often happens, those hands happen to be French-dominated, this results in a subtle but real bias towards French or French-related manufacture and/or design. No surprise that Melbourne started to buy from Alstom.

Quote:
Personally I think Skoda should be linking up with some of these turn-key consortiums when tendering for contracts in the "west" (except the less-prejudiced USA where Skoda and Inekon are doing quite well in establishing a profile). It all comes down to marketing/sales skill in the end.
The problem facing Skoda, Solaris, Pesa, and any non-western, indeed any non-French related company, can be seen in this quote from a recent "Tramways and Urban Transport" supplement on Keolis, one of the leading public transport operators in Europe, and also operator of the Melbourne Trams. Though officially "multinational", Keolis is very clearly French-dominated. Keolis is part of the Tramlink Nottingham consortium, seeking to play a controlling role in Nottingham public transport as a partner to a local bus company. Their UK Light Rail Project Director, Roger Harrison, explained "We are confident we would bring our tramway expertise to the local bus company we would operate with in Nottingham...We know a great deal about integrating trams into a bus network and are familiar with both Alstom and Bombardier trams." (emphasis mine)

There doesn't even seem to be much going for Siemens or Stadler! How is anyone going to get a look in unless they have "The French Connection"?

I don't want this to seem an anti-French rant. They are not the only nationalistic protectionists in the world. As far as Western Europe is concerned, the record of the Italians doesn't seem that much better. And it must be said that most continental European countries have had a much healthier and constructive attitude about public transport - and a correspondingly less fervent worship of the great god automobile - than the Anglo-Saxons. If so many British public transport companies are now owned by continental Western Europeans, then the fault is largely ours in the UK.

Sadly, unless and until they can come to some arrangement which satisfies the French-dominated consortiums, the "Clever Czechs" will not have the success they deserve. However, since our modern "light rail" type tram systems here in the UK have, supposedly, better track conditions than those in the former Communist countries, I suppose it won't matter too much from an operational point of view.

From a tramlover's viewpoint however, it would be great to see the likes of Skoda and Solaris breaking the Alstom-Bombardier duopoly. At the very least it would give us some, in my opinion, aesthetically superior vehicles to look at.
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Old May 19th, 2010, 01:02 AM   #129
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The US is actually very protectionist at the federal government level. Local transit agencies often buy buses, subways trains, light rail vehicles, etc. with partial funding from the federal government, which means that they are subject to "Buy America" regulations requiring products to be made in the USA with mostly domestic materials.

Skoda has a joint venture with Oregon Iron Works, United Streetcar, which makes trams "in full compliance with the Buy-America Act".
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Old May 19th, 2010, 01:38 AM   #130
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Frank H the Variotram (Variobahn in German) has hub motors:

http://en.wikipedia.org/wiki/Variotram#Specifications

It seems that manufacturers like Skoda/Solaris/Siemens and Stadler are going to have their greatest chances where the tram system is owned by the city authority (or state) and there is still the in-house expertise to impartially evaluate tram types. If you get the Thatcherite contracting out of a city's transit (the curse we have in UK and Australia, though thankfully so far confined to Melbourne) then it's going to be Alstom/Bombardier. Unfortunately the trend under the present 'economic rationalist' philosophy is to contract out so we are going to see city transit authorities disappearing one by one, with the French consortiums cleaning up the pickings. In my view the best PT is still to be found in cities with public transit authorities so it's a poor development.

A representative of a European manufacturer I spoke to once said they were appalled over there at the evident lack of expertise in Australia when ordering trams. Tenders have no real technical specifications, just basically "give us a tram". Although, as you say, new start systems have good trackwork, one day things will deteriorate (e.g. in the case of anti-PT governments that throttle back funding) and then they will find themselves in need of a good tram.

I hope we haven't captured the Prague trams thread too much but I hope we've given you guys in CZ some insight into issues we face in the "west" (yes I know, CZ is also in the "west" and Prague is west of Vienna which the Austrians excuse for themselves as being in "South-east western Europe" LOL, all good fun!).

PS Frank, if you make it back to "the continent" just visit Prague, don't bother about the rest, you won't regret it!
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Old May 19th, 2010, 12:03 PM   #131
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I hope my translation will be better to understand than the Google one

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Old May 19th, 2010, 12:25 PM   #132
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Quote:
Rotating bogies in low floor trams

1. Intro

This article describes the relation between the concept of the tram car and the bogie with focus on rotating bogies.
2. What is a rotating bogie
Definition of rotating bogie from script “Rail cars” author prof. Nejepsa (1953) “Bogie is a low cart with two or more wheelsets, with wheelbase 1,8 to 3m even more, caring the bodywork in such a matter the it can rotate in relation to the vertical axis”
3. Bogie is a key component of a low floor tram

LF trams have most of the floor 350mm above the rail that is in the height of the axle of PCC concept tram, like the Tatra T3. Above the bogie the floor is usually little higher. 100% LF are considered trams with floor height up to 450mm with ramps between sections with different floor heights.
To achieve this bogie had to change. The key was replacing the axle of the wheelset with different type of wheel setting
3.1. Rotating bogies with wheels of small diameter
On of the variants is the use of wheels of small diameter. This solution was used in the 80’s and 90’s on trams like Be 4/8 (VeVey) or NGT 8D (Alstom LHB – picture “obr. 2” and “obr.3”). There these bogies with small wheels were placed beneath the middle low floor segment.
3.2. Fixed bogies
The corridor for passengers above the bogies with small wheels was very limited, usually only 500m and the seats had to be on elevated pedestal.
This and the disadvantages of the small wheels could have led to the use of fixed bogies or partially rotating bogies (1 to 5 degrees – like the Škoda 14T comment by me). Trams with these bogies form now the biggest part of the trams made in the last 20 years.
It is clear that the use of 600mm wheel on a rotating bogie would limit the space for passengers very much (obr. 4). Also the use of axle 300mm above rail was not possible. The best solution found was the replacement of a wheelset on an axle with two independent wheels on a welded girder (obr. 5) or on a pivoting beam.
This configuration was used on fixed bogies under the short segment in the middle of a three part articulated tram (obr. 6) under each of the three segments (obr. 7) or under odd segments of a articulated tram with odd bogie segments and even floating segments (obr. 8). The bogies of this concept are on obr. 9 and obr. 10 - Siemens bogie with welded girder and bogie Bombardier with pivoted beams.
The concept of the bogie is related to the system of drive – for example longitudinal motor with a bevel gear or transversal motor with straight gear or a hub motor with planetary gear.
3.3. Other solutions
There are other concepts like portal two wheel bogie on ULF - Siemens, or pivoted four wheel bogies with steered wheels Cobra – Bombardier. They haven’t come to a wider use.
4. Comeback of the rotating bogies
The LF trams with fixed bogies have the problems with the peaks of leading forces when entering the turn because of the small base area that initiates the rotation of the trams into the turn. Differences in the leading forces are on shown obr. 12.
In spite of the economical success of the fixed bogie trams the retreat to older concepts and new innovations has occurred.
Underneath the low floor segments are again rotating bogies with standard sized wheels (Bombardier obr.14 obr. 14). On articulated trams with floating segments under the first and last segment, where the leading forces are major problem, rotating bogies with small wheels are used again (Alstom, Siemens – obr. 15 obr. 16).
Nowadays there are two concepts of driven rotating bogies for LF trams that differ in the concept.
The Citadis class X (obr. 17) has two rotating bogies under the first and last segment and two rotating bogies under the middle segment. The bogies (obr. 18) have two synchronous motors; each drives one wheelset on an axle through a bevel gear.
The Škoda 15T (obr. 19) has a rotating bogie with off-centre bearing underneath the first and last segment and a Jacobs bogie under each joint (obr. 20). The wheels are driven individually by a synchronous motor without a gear only through a short axle between the motor and the wheel.
Both of these trams have a floor height 3500mm above the rail elevated above the bogies with ramps connecting the two parts.
5. Conclusion
From the trends in LF trams design it is clear, that ways are searched to return to tradition concepts.
Rotating bogie is a key component of classic trams and it seams it will be used in LF trams design even more.
I have given it a try.
What is funny is that this article was presented on the "19. conference with international attendance - recent problems in rail cars". I don't know what the foreign guest could have taken from this contribution in czech.

And a link to the porduct sheet of the motor used on 15T: http://www.skoda.cz/?module=uploads&...ad&fileId=1652
each of them has 46,6kW that is close to the Variotram hub motors.
With 12 motors for Riga and 16 for Prague this makes quite a racing tram with up to 720kW for 42t.
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Old May 19th, 2010, 12:40 PM   #133
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If i would looked better I would have found this article referenced to on the Wikipedia 15T page:
http://www.railway2007.fd.cvut.cz/pr...apek+Kolar.pdf
It is much better than the on I translated is in English, but has no examples of real trams.
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Old May 19th, 2010, 04:32 PM   #134
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That's brilliant Sch1 - many thanks!

The only thing that's been misinterpreted I think is that Bombardier Flexity Classic and Siemens NF8 with rotating bogies actually have high floor over rotating bogies (like Skoda 14T). Only Citadis class X and Skoda 15T have rotating bogies under complete 100% low floor - but the Citadis has fixed bogies in the middle section, whereas Skoda Jacobs bogies rotate. Please correct me if you think I'm wrong.

I agree, why such a rare paper is not in English I can't understand! The Capek and Kolar paper has, on the other hand, attracted much interest in the English world.

Thanks again, you have been a great help.
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Old May 19th, 2010, 07:19 PM   #135
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Quote:
Originally Posted by Sch1 View Post
I have given it a try.
What is funny is that this article was presented on the "19. conference with international attendance - recent problems in rail cars". I don't know what the foreign guest could have taken from this contribution in czech.
For most people from Eastern Europe it's quite easy to at least partially understand Czech. Especially when the subject is given and the speach is illustrated with slideshow.
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Old May 19th, 2010, 09:29 PM   #136
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Quote:
Originally Posted by Sch1 View Post
I hope my translation will be better to understand than the Google one
Sch1 - I add my thanks to historywork's to you for your very useful translation of the Zelingr & Heptner paper.

On the Riga trams thread, historyworks had earlier alerted me to the Capek & Kolar paper. Actually to understand better the significance of the Skoda achievement with the 15T, both papers need to be read in light of each other. Now, thanks to yourself, we non-Czechs can actually do that.

historyworks - thanks for the lead to the confirmation that the Variotram/Variobahn has hub motors. Wikipedia is of course not always 100% reliable, but a comment in a book "The Development of the Modern Tram" (good book with many pictures, but not quite as informative on technical engineering issues as I would like) indirectly backs this up.

I have now been trying to find out whether the hub motors of the Variotram are, as I suspect, synchronous motors. Unfortunately the Stadler site doesn't give such info., perhaps because all those interested in buying Variotrams would already know.

In light of Sch1's information that synchronous motors are smaller and lighter than equivalent powered asynchronous motors, I would expect most if not all hub motors to be synchronous. Does anyone know if that is so?

Would it be possible to incorporate an asynchronous motor into a wheel hub in the way I presume that the motor has been so incorporated in the Variotram? If it is not so, then the Variotram must also have synchronous motors, alongside the 15T and the Citadis X (but not earlier Citadis).

In all other cases so far where I have managed to find information on motor-type in modern trams, asynchronous motors have been specified. That is the case with all Skoda trams other than the 15T, with the PESA SWING tram, the Solaris Tramino, Siemens Combino, and Citadis prior to the X series. Thus it still seems to me that the 15T is one of a small minority of modern trams in using synchronous motors. Again this will add interest to seeing how the 15T performs in everyday service.

Incidentally, thanks to Sch1 for the link to the product sheet of the motors used on 15T. They are rather neat looking machines in my opinion.

I apologise if I am hijacking the Prague trams thread with my queries and comments about aspects of tram technology. There doesn't seem to be a thread on this subject - perhaps I should start one, but I've only been a member for a couple of months. In lieu of such a thread, I can't think of a better place to discuss this than a Czech trams thread. "historyworks" has opened my eyes to the fact that the Czech tram industry, especially Skoda, is probably a world leader in tram technology - and shortly one of its most remarkable recent achievements will be taking up everyday service in Prague and Riga.

Last edited by Frank H; May 19th, 2010 at 09:37 PM.
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Old May 19th, 2010, 11:20 PM   #137
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The thing that interests me is that how can Stadler's Variostrams turn so sharp radii?

Stadler Tango tram fro Zurich is 75% low floor and can handle 12m curve in service (that's super achievment, only capable trams now lower than this are Toronto's ALRV and CLRV with 10,89 m of turn radius).

Munich super beautiful variotrams 100% low floor can handle also 14,5m curves.


So how much can Skoda 15T with it's improved bogies? As i've heard only 18m/
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Old May 20th, 2010, 01:48 AM   #138
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Specification of Australian-built Variotrams is minimum curve radius of 16.4 metres but even on minimum curve of 20 metres on the Sydney line the trams go around corners so slowly it is like watching the 'Queen Mary' berthing at a wharf! There is also now talk of premature rail wear on the line. The trams are also fitted with flange lubricators (as are all modern trams). So perhaps it is true in theory that such fixed bogie trams can go around small curves, but so slowly and with such wear issues it is an operational problem. In the Toronto tender the Bombardier tram failed the transit authority's derailment test originally! And in Helsinki the Variotrams had big problems, I don't know if entirely for this reason or other reasons too.

Skoda 15T bogie pivot spec is down to 15 metres (in depot) but don't forget its pivot is still limited to about 25 degrees compared to (I think) about 40 degrees on a conventional high floor tram (but still a hell of a lot better than 1-5 degrees which is the best achieved on any 100% low floor tram). If you want to know why fixed bogies aren't such a great thing on curves watch this video of Citadis on a very mild curve in Madrid - turn the sound up on your computer (and wear earplugs!). Not how to "sell" the concept of light rail to a sceptical public:

http://www.youtube.com/watch?v=s2p_HV2W-Os

A bit of information on the Australian Variotram (but doesn't answer Frank H's question on the hub motors - if I meet the operator some time I will ask the question):

http://www.sleeper.apana.org.au/railway/slr/
(scroll down page for information on the tram)

http://www.metrotransport.com.au/PDF...lTechSheet.pdf

In countries like Australia and UK we are trying to "sell" the benefits of the tram compared to the bus that has dominated our public transport systems for so long. It doesn't help the image when the trams crawl around corners like caterpillars while buses can whizz around quickly! Travelling by tram in Prague by contrast is an eye-opener and a thrill for speed demons!

Frank H, not many in the "west" realise the scale of the Czech tram output. More than half the world's trams (some 23,000) are Czech, mostly Tatra with products on systems all the way from Europe to the Philippines. Successful is an understatement - the T3 (and T4 variant) number about 17,000 alone, the world's most numerous and successful tram.

However you will find Czechs on this forum more critical of their own trams (ungrateful! ) and I think some can't wait to see the last of the T3s. Personally I love the T3, like a classic thoroughbred racing car



http://en.wikipedia.org/wiki/Tatra_T3
http://en.wikipedia.org/wiki/Tatra_T4
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Last edited by historyworks; May 20th, 2010 at 02:04 AM.
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Old May 20th, 2010, 08:02 PM   #139
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http://www.youtube.com/watch?v=s2p_HV2W-Os
About this video you're mistaken I know spanish very well,., it's run videos prior to inauguration so trams are new and the rails are not fitted yet to wheels so that's why the squeal. it's not sharp curve.


About chzech trams, T3 is different model and T4 is different model, it's not a modification, it's different.

The msot numerous tram in the world till now is Russian four axle very well known model KTM-5, the number of this trams are 14369 .
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Old May 21st, 2010, 01:25 AM   #140
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Quote:
Originally Posted by Tramwayman View Post
http://www.youtube.com/watch?v=s2p_HV2W-Os
About this video you're mistaken I know spanish very well,., it's run videos prior to inauguration so trams are new and the rails are not fitted yet to wheels so that's why the squeal. it's not sharp curve.


About chzech trams, T3 is different model and T4 is different model, it's not a modification, it's different.

The msot numerous tram in the world till now is Russian four axle very well known model KTM-5, the number of this trams are 14369 .
Madrid - but the rails are set in concrete. Do you mean the grinding hasn't happened yet? It is hard to see what more they can do between trial and inauguration. The trams would have to be using their flange lubricators to eliminate noise surely, there is not much more to do to the track?

Thanks for alerting us to KTM5 Tramwayman - looks like it's across the line by a nose (a few hundred more than T3). How many still survive? I am surprised at the number. I thought Czechoslovakia was the designated tram manufacturing country in Comecon although I know Poland and Russia (and apparently Latvia) still manufactured some of their own, but T3/T4 was still the most successful (and technically superior) export.

I understand that in the current generation there are about 43,000 trams in the world. If combined Czech and Russian trams number about 37,000 that places the real "significance" of trams in "western" countries (the only trams we ever hear about in the "west"!) in true perspective! (I gather there were about 8,000 trams produced in postwar West Germany, the only significant postwar western manufacturing country, so the differences on both counts would be down to trams scrapped during this period I guess.)
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