Motors and Gearboxes, Notes on Types and uses.

[bertiedog]

Motors and gearboxes, uses and notes.

The start of this thread are the notes from the Old RM Forum. I have tried transferring the content, (with comments), with the transfer facility but to no avail at the moment on my computer. So my apologies to all who replied to the old RM Forum posting, I have edited out most comments purely to leave the basic text, no reflection is intended in any way to any previously posted comments.

Feel free to re-post any queries on motors to this thread here as a reply.

 

Stephen

 

 

The intention was Part One on motors, and so on with gearboxes and universal joints, but this post is a pr?©cis of the old parts to date, with more to come soon.

 

Part one

 

I think it must be worthwhile to post a few notes on motors and gearboxes, as so many opinions and queries are posted on RM during postings about loco building in general.

Having had long experience in modelling, both professional and private, I have gathered up a lot of experience with this and feel the notes should help both old hands and newcomers to the hobby.

 

Some basics first about motors

 

Our models run on DC motors, even with DCC control, and the basic requirement is a DC motor that runs on 0 to 12 VDC at a reasonable current, and the main type that for meets the requirements for this is the Permanent Magnet Direct current motor.

 

There are two basic types these days, Coreless and Conventional Multi Pole motors. The coreless DC motor was developed for instrument use, low current and light duty, but very well built. They have a disadvantage, despite all the plus points in that the main shaft usually cannot take an end thrust, and require special gearboxes to apply the power to the track.

 

The multi pole motor is usually chosen as it is simple to design and build and experience has shown that the basic design is very reliable indeed.

 

The first motor makers for model railways were Mantua in the United States, in the 1930's, who designed a range of small 6 volt DC motors, later altered to 12 volt DC in the 1940's.

 

In the UK the most popular of early 4mm scale OO locos were fitted with 6 volt motors, conventional designs for the 1930's period, later altered to 12 volts as it gave more reliable operation. Stewart Reidpath were the first UK dedicated motor maker, for his HO models in the 1930's.

 

AC operation, as with O gauge had been considered and used, but was not easy to fit to the tiny locos in 4mm scale. the motors need a reversing mechanism and there is little space in such a model. Marklin in Germany were the only maker to persist with the design.

 

With Direct Current the situation is easier all round, and Hamblings in the UK were the first to use 12 volt DC open framed motors commercially, built for them by the British Motor manufacturer Taycol. These were state of the art, and still a sound and very expensive design, ball raced, and the shaft was supported and both ends with an "in frame" gearbox.

This general style was adopted by Romford and Zenith, who introduced motors after the war along modern design principles.

 

Zenith made a seven pole motor with a brass frame that is still considered to one of the finest motors ever designed.

Rather regrettably the cost was high, and Zenith were taken over by Tri-ang who used Zenith to make the XO series of motors, fine in their way, but cheaper to make and greatly simplified design and build quality.

 

Mantua's pre-war design in the States was adopted by Pittman, who was an enthusiast owner of an electrical supply company, with an interest in motors. His own models were O gauge US trolleys, but they developed a range of classic open framed motors, about the finest made at the period, and still a very sound design. They were also involved with Varney and Lindsay, making Lindsay's then unique ring field motor, which was copied by Meccano in the Hornby Dublo range later on.

 

By about 1950 all the designs were settled, and the conventional motor in it's open framed form remains the main type of motor used in conventional model railway designs, ranging from 3 pole to 7 pole types.

 

An early user of Pittman was Formo/Preen in the UK, ( Graham Farish), when Farish had troubles producing a good motor of their own design, succeeding only in designing a unique and ghastly Heath Robinson 2 pole motor. Not really their fault, it was the wartime restrictions that lingered on after the war that meant they were forced to use an odd design to get around the rules.

 

Meccano remained aside from the conventional designs , preferring to build the motor in to the Dublo chassis as a unit, or using the Ringfield principle as in the Castle motor. This was based on the Lindsay, but had not got full ballraces and only had a conventional 3 pole armature, to lower costs.

 

Now a major point, there is absolutely no difference between a cased motor, with a can cover, and an open framed motor, both have the same electrical characteristics and performance, The magnets may be a pair, but act as one and the same as a block magnet. The can motor can also have a ring field magnet, which again promotes smooth operation and efficiency, unless it is cheaply made by Lima of course!!!

 

The can motor was developed from the Toy industry in Japan, a simpler way to make a motor, by using a drawn steel case and cheap cast alnico magnets, cheap to make, but not better or worse than an open framed motor. Quality depends on cost, and vice versa.

The can motor was developed by Japanese makers, adopting ring magnets in some, and higher quality materials , until we have as an example today, in the Mashima Types. Most have powerful rare earth magnets like neodymium.

 

The basic commutator and armature remains the same design across the years, usually a three pole or more type, with seven being considered the best option, but rarely made due to cost these days.

 

The more poles the smoother the motor, as each pass of a magnetic pole causes cogging, a jerk in the rotation, so a greater number of poles will help with the smoothness. Lindsay invented Skewed or twisted slot motors, where the pole overlap smooths the operation.

 

The commutator and brushes work in exactly the same way in all motors, it is the application and quality that varies, for instance the Old K's motor used the same design basics as Mashima, but K's are awful, badly made and un-reliable, but the Mashima work due to the quality of the parts.

 

In the UK the next design changes in the late 1950's came from another use, in electric slot cars, and as these became popular they governed the design of cheaper motors. Many makers adopted the cheap and cheerful simplification of design, and quality suffered badly in the model railway field.

 

Tri-ang did make reasonable 3 pole motors, but only in the mass RTR market, and cheap design governed the quality. Romford and other's like MRRC keep making standard designs , but costs spiralled in the UK, and the comparison with imported designs began to finish them off in the 1980's.

 

Another deep problem in the UK was the gears, made by only a couple of makers, who simply could not produce concentric or accurate gearsets in the 1960's onwards.

 

Most open framed motors use a worm drive, a worm on the motor shaft and a gear on the axle, but if either are inaccurate then the whole thing is poor engineering and at worst, complete and utter trash.

 

The main changes in the UK came in the 1980's when can motors from Japan and the far east became more available, and gearsets were made to reasonable accuracy. It became popular to add a folded etched metal frame to act as a gear box, screwed to the end on the motor, which helps assembly of an accurate gear mesh.

 

This is the current situation, can motors, some times round, sometimes flat sided, occasionally semi open Far Eastern motors, fitted to etched frames which fit between the frames, sometimes allowing side play for axles that require it. There are several producers, and multi fit designs, all work well if assembled carefully, but some need great attention to detail in assembly.

 

In the States the design went down a different path, a motor separate from a gearbox, with a universal joint to the motor. This allowed a bit more flexibility of mounting, and application. The open framed motor remained popular a lot longer due to more space in larger models. The can motor has now taken over due to cost and design improvements,

 

As US made motors went off the market due to cost, etc, the Japanese motors took over, but the basic design remains the same and price is the main indicator of the quality.

 

Now all of this refers to scale models, not toys or RTR types like Bachmann, Airfix, Hornby, and a thousand others, who all have designed both good and bad motors and transmissions, mainly governed by cost, not design excellence.

 

There have been crossovers between the types, Tri-ang were used in scale models, but mainly because there were freely available, not by choice. In the UK the better makes like Taycol have long gone, and the better models use coreless motors, German and Japanese made.

 

Portescap in the UK combined a coreless motor with a Swiss gearbox, and got good results, but it needs care to fit and a very sound appreciation of the engineering to get the best from them.

 

A big source of good motors have been the Japanese electronic industry, like Canon and Aiwa (Sony), who have made small motors for other uses that have found their way into model designs.

 

Canon make fine motors especially for models as well, but mainly larger types that dual as mechanism motors as well. They pioneered the use of gearhead motors, where an in line encased gearbox is built into the motor. These are not much use as motors for trains as the gear output still has to be turned around at 1:1 by a worm gear to get the drive to the axles. But such gears are now available and this type of motor offers very powerful and silent operation..

 

As can be seen from the above notes, the variations are legion, but the principles of operation remain the same, despite the dozens of types of motors. Motors should have a wide power characteristic, be well made, have serviceable bearings, be they plain or ballraced, decent brushes that are replaceable, and the vital point is that the gears must be top quality, the most important point of all.

 

You should not be able to hear a motor running on it own, and in the loco it should be smooth and quiet, no jerks, jitters, binding, slowing and pausing or any other problem. The loco should have enough power to operate a train, and under strain there will be a bit more noise, but no rattles or excessive mechanical noise.

 

Gears are vital, and all I can advise is go to a maker who actually manufactures them like Ultrascale, or source from a specialist maker to industry, expensive but worth it. The typical worm and gear drive sets in the UK now are not too bad at all, and with care fitting work fine. If you have a lathe and home workshop it is quite practical to make them yourself, but it is somewhat complex, but again worth it to get complete accuracy.

 

Part two will cover the types, mounting and gear frames and boxes, and Part three will cover universal joints and tender drive motor mounting, all simple home mechanics work, or easy application of commercial items.

 

Coreless motors

 

 

A bit extra on motors and this is about the Coreless type, which has a lot written about it and a lot of miss information.

The Coreless motor is an ordinary motor turned inside out!! it was developed from an earlier type, the Distler type, in which the wire coil magnets remained stationary, and a permanent magnet on a shaft rotated.

 

This was first used in the Model railway field with the introduction of the Graham Farish motor after the war. The design used two coils, on on the top of the motor, and one on the bottom, with a shaft and magnet running through the middle.

This only allowed the use of a two pole magnet, and therefore the motor was a two pole type.

This has an inherent problem in that it is not self starting!!!!! a major problem. Farish were electrical and radio engineers and the design was proceeded with despite this problem, as they came up with an ingenious solution.

 

The commutator was replaced with switchgear, on the end of the motor, which applied pressure to the armature to always stop in a position where the motor could restart.

 

However in a model train we have no idea just where the motors will have to come to a stop, and re-start, so Farish were forced to add a clutch, which allowed the motor to coast to a halt on it's own. But it also meant that the clutch had to engage abruptly as the loco moved off, hardly a plus point.

 

Also it was found that the contacts did not always return the motor to the correct position, wear and tear etc., got at it, and often the loco had to be pushed to start. But the motor was surprisingly efficient, rivalling modern designs, low current and lots of power.

 

The related Distler type used some of the ideas, but solved the problems of the Farish. The first type had a multi pole magnet on the shaft, and multi coils, making a superb design, but the magnets were complex to make, and they then came up with the grand daddy of coreless designs, placing a permanent 2 pole magnet stationary in the middle of a rotating coils.

 

This type found it's way into model railways in early Joeff Trains, but was developed by the instrument motor industry into the coreless type. Having low mass they suited servo mechanisms in aircraft displays etc. The main problem at first was the magnet got in the way of the shaft, and was solved by making the shaft come from one end of the motor only, but introducing the problem that coreless motors cannot take an end thrust.

 

The armature became coreless by potting the wire in resin, and using no metal at all to support it, with the close fit possible the magnetic field is far stronger and the motor more efficient. The coils are like a basket closely fitting over the magnetic core. The number of poles can be increased as far as the design will take, and the design is naturally smooth as there is no magnetic cogging.

 

There is still brush gear attached to the coils via a commutator, but because of the delicacy of the coils, they design these with gold commutators and specialist brushes that do not need replacement in the motors lifetime.

 

Generally the motors are super efficient, low current, and because of the lack of cogging, very quite, and as most are designed for instrument use, they are ballraced as well.

 

If the coreless motor is single ended shaft type, then it cannot take end thrust, and prefers suitable spur gears or a universal joint to connect it to a gearbox. If it is double ended usually they can take end thrust, and have worm gears fitted direct.

 

There are no model railway designs as such, suitable motors are picked from other uses, which range from high end Hi-fi to instrument drives in aerospace uses. They tend to be expensive, but the smaller types are available quite cheaply as they are mass produced. A noted maker is Faulhaber in Germany.

 

Portescap in the UK marketed coreless on a Swiss gearbox, and very nice but expensive motor unit. I believe that they are not made now, or only in limited batches.

 

Coreless need care to use them, they do not like overloading, and on DCC need a special chip to handle the low current and different impedance of the motor. Performance on DC is superb, no type of motor can beat the slow speed operation and silence.

 

Re: Motors and gearboxes, uses and notes.

 

 

The modern motors are higher power at all revs, due to the magnets, close gaps, and also better grade steel in the armature, but also tend to have a high end peak, and that is not actually what is wanted for Locomotives.

 

The motors does work as soon as it starts rotation, and this is from zero, requiring the current supplied to be converted to mechanical effort right from the first application of voltage.

 

The most efficient of the motor designs is the coreless, with no metal core losses, and efficiency is remarkable at low revs, with motors able to idle at very low revs. There is no cogging to overcome like a conventional motor, so the start is easy, all electrical power is converted to mechanical, bar usual mechanical losses.

 

All conventional motors have magnetic cogging over each pole, magnetic drag, which is overcome by the applied electrical power, but tends to come on in a burst, leading to jerky starting. More poles help here, and seven should be the minimum, five are acceptable. Skewed slots help as well, these cause an overlap of each transitions of a pole, making it smoother, and easy to start to get moving. Windings also make a difference, star winds are better for our uses, but are rarely supplied as it is more costly to wind and connect up in production.

 

The art of design of the components is to reduce starting effort being applied to soon, or too late.

 

What a motor returns in fractional horsepower at higher revs is of very little consequence( unless it falls), as the gear ratio is in full play, and if the motor has enough power to get moving, all others things being equal, does not acquire an increase as the revs get higher. Measured via a gearbox the measured horsepower increases with revs due to mechanical advantage.

 

All motors have theoretical max output, at a given current curve as the voltage is increased.

 

Ballrace bearings are much more efficient than plain, especially at the vital low revs as the loco starts moving. Figures vary, but anything from 10% to 20% can be gained, the highest figures for high speed rotation. Also they remain quiet, no wear, so no increase in noise.

 

It is not for the user to adjust the brushes, this is not needed. but it makes the motor serviceable later one in it's life. It can help to slacken brushes on a new motor, if a loco is say a shunter, as the friction will be somewhat lower and slow running better.

 

There is no one solution that fits all, different motors are needed for different uses. The Mashima range covers about all requirements, but could be improved, at a price, with ball races.

I have modified several Mashima tube can motors with Borden instrument ball races, added to the ends externally, with the bronze bearings removed. It also makes the motor suitable for a flywheel on the motor shaft, risky with plain bearings.

 

Can motors have fewer parts and therefore cheaper to make, as Johnson in Hong Kong found out, making toy motors for pence.

 

A open frame has better ventilation and easier to adjust brushes, but no actual advantage over a modern design, like Pittman instrument, Canon, or Buhler etc, and open framed have fallen from use, my point is that open framed does not mean a bad motor

 

 

alcazar wrote:I'm sure I've read an article, some years ago, in which someone took apart an o/f motor, removed all the windings, then split the laminations and skewed them, then rewound it to make it a better, smoother motor.

 

Or did I dream it?

 

 

Virtually any 3, 5 or 7 pole armature could be altered from straight slots to skewed slots. it reduced magnetic cogging, making the motor start easier and run quieter at all revs. There is no reason not to fit it, apart from cost.

An armature is easier to wind with straight slots, it is as simple as that. You can re- wind them at home, it is not easy with 7 poles, but you can easily do it with 3 poles. The problem these days is the epoxy resin used to stack the laminations, it needs heat to shift it and re- assemble. A lot of work to alter an old motor.

You can also Star Wind the armature, where the wires are taken from each segment of the commutator and not wire to the next, but to the tail connection of the next poles windings. The current return path is via the next poles windings, which is out of magnetic reaction at that point, reducing the over-all current, and smoothing the action of the motor, with a slight loss of power overall, but most motors can spare it.

 

Makers like the Japanese, on 5 pole motors etc, do not usually star wind, as it costs more with extra soldering and insulation, so costs more to do.

 

 

Re: Motors and gearboxes, uses and notes.

 

As it has come up in postings, Ringfield should be mentioned. This is a type of motor, not a single commercial motor. As mentioned before the main problem with conventional poled motors is that they "COG".

 

With any kind of magnet the field is applied a two poles, and however many poles the armature has, each one has to force its way past the magnet. This jerks stops smooth starts, and creates noise at higher revs, it is the purr that you hear from running an un-loaded motor.

 

More poles eases the problem, but skewing the poles till they overlap is the next answer, along with star winding of the poles, a special trick way of connecting each poles wiring.

 

The next improvement is the can motor, the fully machined thicken steel type, where the magnetic poles are still concentrated to allow operation, but the case acts as a shunt and allows smoother operation.

 

This is not the same as a simple can motor, which may still contain two magnets, or a side magnet as with pancake motors.

 

The answer is the Ringfield, which was designed by Lindsay, and used by Meccano in Dublo locos. Now Meccano did not fully implement the design, using a plain armature, not skewed, although they did star wind some 1950's production.

 

The Ringfield is a solid ring of magnetic material, with poles induced in to the ring, which act in the same way as separate magnets, but whole magnetic field is smoothed out in the transition between the poles, reducing cogging with little loss of power.

 

With a minimum air gap, Ringfield magnets, a skewed slot armature, with a star wind, and ball bearings, you have a perfect basis for a de-luxe design for a model railway loco. Ringfield motors that work are Meccano's Castle type,( as long as not a Binns Road Friday afternoon job), and the types that are poor are Lima and Hornby, where the air gap is large, the materials plastic, and often with poor commutators and poor main bearings.

 

Stephen.

[jmg123]

I wonder if eventually railways will follow the path that the RC world is taking and start using brushless motors? They work great in my helicopters, much smaller than a comparitive brushed motor, very quiet, very effecient, no cogging, and mountains of torque. If i'm not mistaken the 21 pin dcc "standard" can take 3 hall sensors and has 3 motor ouput wires, does anyone know of a decoder that supports these features though?

[Miss Prism]

The 'mountains of torque' derives from the mountains of amps they consume.

[bertiedog]

I wonder if eventually railways will follow the path that the RC world is taking and start using brushless motors? They work great in my helicopters, much smaller than a comparitive brushed motor, very quiet, very effecient, no cogging, and mountains of torque. If i'm not mistaken the 21 pin dcc "standard" can take 3 hall sensors and has 3 motor ouput wires, does anyone know of a decoder that supports these features though?

 

It is an interesting point, but not really practical for locos. The reason that the three phase AC brushless motor, which is what is being used in aircraft, are popular, is the power to weight ratio, which is exceedingly high with efficient AC motors.

 

But I hear the reader say, these are not AC motors, they run on battery packs in the aircraft, not AC mains.

 

Well, what is used is a 1/2 wave approximation of three phase AC operation, three power pulses per rotation delivered in sequence by the electronics, and in other cases by hall effect sensors and control electonics, to drive the AC brushless motor. The brushless motor still has magnets, usually neodymium, with the coils held stationary, and the magnets in the housing driving the housing and the propeller.

 

The low weight is vital, as is the extreme efficiency, but ordinary coreless DC motors are even more efficient, and already widely used in Model railways.

 

The aircraft engines require complex and very robust control circuity, and adding this to DCC, for instance, would make a lot of extra electronics doing very little in a typical loco. A coreless DC motor can operate from the DCC chip direct, and offers the best all round efficiency and control.

 

Although control of the motor is achieved in the aircraft, it is not the sort of exact control of speed from zero to max in a smooth stepless progress that we have in Model Railways.

 

The aircraft basically need a start position, then a simple increase to get moving and finally full power, with the ability to throttle back to save the battery pack, to increase the duration of the flight, very different from the delicate precision required for locomotive models.

 

The only area that they might be more widely usable is with large scale locos, 5 inch gauge passenger hauling, where they are starting to be used with full electronic control, the main requirement is brute force, without the heat losses of DC motor control circuits.

 

Hope this helps,

Stephen.

[Pugsley]

Interesting, that way you could do a large scale version of one of these beasties:

http://www.northeast.railfan.net/images/tr_sp267.jpg

 

With the proper AC transmission! B)

 

Just need a miniature 16 cylinder and alternator to go with it now

 

Thanks for the notes Stephen - very interesting indeed!

[Brian Harrap]

Fascinating read on motors Stephen, I have learned a lot. However I am still struggling with the (single ended) coreless motors won't take or don't like taking end thrust piece. Under the 'Harrap talks twaddle' banner may I ask if I am missing something? I have taken apart several single ended coreless motors of various makes for various reasons not least just to see what was inside and also to convert sinle ended into double ended types. (Another story that - and do you know why the double ended are so difficult to get hold of?) All the ones I have disassembled appear to have an adequate, if primative, circlip taking up thrust in one direction against a collar of sorts in the other. Also, I have several single ended types that have been running for years in my small scale locos with a worm gear fixed directly to the output shaft with, as far as I can see, no detrimental effects. The Portescap motor/gearbox combination, as I am sure you know uses a bevel drive mounted directly to the motor shaft surely producing some amount of end thrust although admittedly only one direction. I am aware that early production types had a needle type bearing at the com end (much commented upon at the time in the US MR mags) and of course that would not support end thrust. As I say am I missing something here, I would very much like to know what you make of it all. Regards Brian

[richard_t]

I hope the following are useful, links to manufacturers of coreless motors:

 

• Portescap
• Maxon
• Faulhaber

Portescap are still going strong - I think it's just the RG4/7 gearboxes that aren't made anymore.? 

[bertiedog]

Fascinating read on motors Stephen, I have learned a lot. However I am still struggling with the (single ended) coreless motors won't take or don't like taking end thrust piece. Under the 'Harrap talks twaddle' banner may I ask if I am missing something? I have taken apart several single ended coreless motors of various makes for various reasons not least just to see what was inside and also to convert sinle ended into double ended types. (Another story that - and do you know why the double ended are so difficult to get hold of?) All the ones I have disassembled appear to have an adequate, if primative, circlip taking up thrust in one direction against a collar of sorts in the other. Also, I have several single ended types that have been running for years in my small scale locos with a worm gear fixed directly to the output shaft with, as far as I can see, no detrimental effects. The Portescap motor/gearbox combination, as I am sure you know uses a bevel drive mounted directly to the motor shaft surely producing some amount of end thrust although admittedly only one direction. I am aware that early production types had a needle type bearing at the com end (much commented upon at the time in the US MR mags) and of course that would not support end thrust. As I say am I missing something here, I would very much like to know what you make of it all. Regards Brian

 

The end thrust was a carry over from the Distler designs where the magnet was in the middle and would have had to be accurately drilled and machined to allow the shaft through, and Alcomax and other alloys were difficult to drill and machine. This led to making a recess in the end and using a single shaft with the commutator on it, all at the same single end.

 

Some designs can indeed be converted to take end thrust, and some that have the single end design can take modest end thrust anyway. Changing to a through shaft depends on the original design, no hole through the magnet means no shaft!

 

It is never a good engineering idea to have the motor taking the thrust anyway, so using bevels, spur gears, or a worm with a universal joint, is so much better.

 

Most of the brushed Coreless motors were used for precision feedback controlled operation in instrument drives, an area of industry that they have been replaced in, by brushless coreless AC/DC motors, driven from DC by producing AC voltage control via electronic control circuitry.

 

In effect thay are controlled exactly like a stepper motor, a system that does not really suit Model Railways at the moment. It is widely used in model aircraft, for other reasons, efficiency and weight, and brute power.

 

Any coreless motor is best isolated from the thrust by a joint, and separate thrust arrangements made in the gearbox, a proper approach to the design. But really this applies to all motrs as well, it is better to have the thrust taken by proper thrust washers or ball races.

 

Stephen.

[Brian Harrap]

The end thrust was a carry over from the Distler designs where the magnet was in the middle and would have had to be accurately drilled and machined to allow the shaft through, and Alcomax and other alloys were difficult to drill and machine. This led to making a recess in the end and using a single shaft with the commutator on it, all at the same single end.

 

Some designs can indeed be converted to take end thrust, and some that have the single end design can take modest end thrust anyway. Changing to a through shaft depends on the original design, no hole through the magnet means no shaft!

 

It is never a good engineering idea to have the motor taking the thrust anyway, so using bevels, spur gears, or a worm with a universal joint, is so much better.

 

Most of the brushed Coreless motors were used for precision feedback controlled operation in instrument drives, an area of industry that they have been replaced in, by brushless coreless AC/DC motors, driven from DC by producing AC voltage control via electronic control circuitry.

 

In effect thay are controlled exactly like a stepper motor, a system that does not really suit Model Railways at the moment. It is widely used in model aircraft, for other reasons, efficiency and weight, and brute power.

 

Any coreless motor is best isolated from the thrust by a joint, and separate thrust arrangements made in the gearbox, a proper approach to the design. But really this applies to all motrs as well, it is better to have the thrust taken by proper thrust washers or ball races.

 

Stephen.

Thank you Stephen, maybe I should treat my Faulhabers a little more gently, Brian

[Giles]

Stephen - a genuinely fascinating exposition. Thank you very much for taking the trouble to explain it all so clearly!

 

 

Giles

[S.A.C Martin]

Hi Stephen,

 

Just been reading this thread - absolutely fascinating! I have a small query if that's okay.

 

What are the advantages of having an all wheel drive mechanism that is to say, for example, in a 4-8-2 locomotive, the driving wheels are all powered by having gears on each axle and smaller, identically ratioed gears between them, e.g:

 

OoOoOoO - the rear set powered by a motor utilising a worm gear, as opposed what I perceive to be the standard, a powered axle coulped to other driving wheels by connecting rods?

 

I am looking over a friend's ideas for a model locomotive I am trying to design, and the suggestion of a chassis with all wheels powered, as it were, came up.

 

Kind Regards,

 

Simon

[bertiedog]

Hi Stephen,

 

Just been reading this thread - absolutely fascinating! I have a small query if that's okay.

 

What are the advantages of having an all wheel drive mechanism that is to say, for example, in a 4-8-2 locomotive, the driving wheels are all powered by having gears on each axle and smaller, identically ratioed gears between them, e.g:

 

OoOoOoO - the rear set powered by a motor utilising a worm gear, as opposed what I perceive to be the standard, a powered axle coulped to other driving wheels by connecting rods?

 

I am looking over a friend's ideas for a model locomotive I am trying to design, and the suggestion of a chassis with all wheels powered, as it were, came up.

 

Kind Regards,

 

Simon

 

Best to go for a single powered axle, and one that depends on the exact arrangement of the loco, but the second or third axle would be best for the gearbox.

 

The Coupling of the axle with spur gears is basically a Toy train makers method, pioneered by Marklin etc, where the gears take the drive, and rods are cosmetic. This is all right on an Ho model, they are not scale chassis, (ducks from enthusiast denying that!), and have a lot of dimensions altered to allow the gear train behind the wheel sets.

 

This gives a somewhat off set chassis, which may not fit a UK design with splashers etc, which have tight clearances in OO scale..

 

Finding spur gears to the correct pitch circle and sizes would be difficult, although by luck standard sizes might fit. Also the spur gears cover the backs of spoked wheels, and would need to be pierced to allow light through spokes wheels, to give a normal appearance.

 

There is no need for all the complexity, plain rods and a single driven axle are more efficient and work fine.

 

Stephen.

[S.A.C Martin]

Best to go for a single powered axle, and one that depends on the exact arrangement of the loco, but the second or third axle would be best for the gearbox.

 

The Coupling of the axle with spur gears is basically a Toy train makers method, pioneered by Marklin etc, where the gears take the drive, and rods are cosmetic. This is all right on an Ho model, they are not scale chassis, (ducks from enthusiast denying that!), and have a lot of dimensions altered to allow the gear train behind the wheel sets.

 

This gives a somewhat off set chassis, which may not fit a UK design with splashers etc, which have tight clearances in OO scale..

 

Finding spur gears to the correct pitch circle and sizes would be difficult, although by luck standard sizes might fit. Also the spur gears cover the backs of spoked wheels, and would need to be pierced to allow light through spokes wheels, to give a normal appearance.

 

There is no need for all the complexity, plain rods and a single driven axle are more efficient and work fine.

 

Stephen.

 

 

Thank you Stephen for the prompt reply

[hollywoodfoundry]

I echo Stephen's answer, but would add that a further issue in having gear drive to each axle may make quartering of the wheels a little more difficult, and can also cause binding of the coupling rods.

[bertiedog]

I echo Stephen's answer, but would add that a further issue in having gear drive to each axle may make quartering of the wheels a little more difficult, and can also cause binding of the coupling rods.

 

Have a look at most continental H0 chassis, the rods have oversized holes or oval for just this reason, very nice engineering! One alternative that may apply in O gauge is the use of chain drive, the delrin plastic type, to couple the gear box to the driven axle , and is used on diesel bogie chassis to couple wheels, saving an in line drive shaft and a gear on each axle.

 

Stephen

[jamie92208]

Just a point about Coreless motors. Portescap is not a motor manufacturer. Escap is the name of the motor manufacturer and Portescap was a motor/gearbox combination which was I believe manufactured in Portishead but using Escap motors. Buhler also made motors. There are several gearbox makeres in the 7mm world who now make gearboxes that will fit the Escap range and I use Ron Chaplin gearboxes successfully on some large Escap motors in my 0 gauge locos. Several of us in the Wakefield club have identical motor gearbox combinations in our variuous Midland Locos. These have run successfully for some years with a worm gear then two reduction gears.

 

Jamie

[richard_t]

Just a point about Coreless motors. ? Portescap is not a motor manufacturer. ? Escap is the name of the motor manufacturer and Portescap was a motor/gearbox combination which was I believe manufactured in Portishead but using Escap motors. ? 

Interesting as their website is clearly? ? Portescap - and the motor I have sat in front of me is marked "Portescap" (a 22N 28 210E 204 to be precise).

[gz3xzf]

Sorry to resurrect this dormant thread, but I wonder if it would answer a question I have, I am building a kit which requires the addition of a motor and gearbox. Now I found the above interesting about the types of motors that exist but it didn't really go into what I was hoping for.

 

How do you decide what gearbox ratio to use?

 

I have decided what the maximum speed of the loco might have been (around 70MPH), as I know the wheel diameter I can calculate how many revolutions per second is required to get that speed, but I haven't found anywhere the speed of the motors so that I can tie the wheel speed to the motor and hence decide what ratio gears I need?

[bertiedog]

Given a normal 3/5 pole motor, equivalent to Mashima, then 40:1 for fast larger wheeled locos, and 60:1 for shunters, with 50:1 as general purpose. Diesel power bogies require lower ratios, even as low as 20:1.

 

Coreless motor types need higher ratios generally., they develop power at higher revs.

 

On the High level gearbox site are recommendations, and other sites as well.

 

Stephen

[Daddyman]

Sorry to resurrect this dormant thread, but I wonder if it would answer a question I have, I am building a kit which requires the addition of a motor and gearbox. Now I found the above interesting about the types of motors that exist but it didn't really go into what I was hoping for.

 

How do you decide what gearbox ratio to use?

 

I have decided what the maximum speed of the loco might have been (around 70MPH), as I know the wheel diameter I can calculate how many revolutions per second is required to get that speed, but I haven't found anywhere the speed of the motors so that I can tie the wheel speed to the motor and hence decide what ratio gears I need?

Ask Chris at High Level - he has a way of calculating these and will read them out to you over the phone. 

[DCB]

It would probably have been better to start a new thread.   However there is no simple answer.   Motors vary. Many are 8 volt motors which can run on anything from 2 to 20 volts without too much distress and many will achieve the same speed at the same control settings whether on 20:1 or 40:1 gears.  Only light engine speeds and ultra slow speeds really change though the frenetic scream of low geared motors is very irritating to me.  15 000 rpm is a figure often mentioned but you are talking off load here and I doubt many motors get much above 8000. Again the spec but I doubt it will tell you much.  

 

Do you want to drive your locos flat out?  My Wrenn Gronk on 60:1 gears more or less has one speed, flat out, as does my Ring Field motor 56XX running Triang gearing, This very low revving motor runs at max revs makes it very stable as regards speed but very frenetic to listen to.  Older higher geared Hornby Dublo locos are much nicer but need driving as they run away down hill.  

 

Probably best to ask at exhibitions, not about the locos which run nicely but the horrible ones that scream like a band saw, or take off like a scolded cat, that way you learn what to avoid.

 

As a rule of thumb the bigger the final drive gear the smoother the loco will run

[gz3xzf]

Thanks for the answers gentlemen: -

 

David, I didn't start a new thread as this seemed to have a lot of useful information and was sort of going the way I wanted. I know what you mean about the scalded cat, My son has a Hornby Smoky Joe that we fitted a Hornby DCC chip to and it is uncontrollable at high speed, I added about 75g of lead to try to get it to work at slow speed (i.e. to help it stay connected to the rails) and this made it a lot better, but I think the gear ratio is too low.

 

Recently I have been testing the speed of a loco when I fit a DCC chip, I measure the flat out top speed of the light loco to get an idea of the maximum scale speed, if it turns out to be too high (i.e. the scalded cat) then I turn down the max voltage (generally CV5) so that it does what I consider to be a reasonable speed for the loco (e.g. an express with 6'8" driving wheels: around 90 to 100MPH; a L&Y Pug with 3' drivers around 30 to 35MPH). This is not always possible (i.e. the Hornby decoder) as CV5 is not always enabled.

 

So when it came to the new kit I wanted to find if there were some calculation I could use to find the ratio required, from the wheel diameter, the maximum speed required, etc.

 

Daddyman, I will give High Level a ring so that I can see what he thinks.

 

Thanks again for the replies.