Flywheels in small 4mm shunting locomotives

[Ruston]

Evening all,

 

I would like to know people's opinions on fitting a flywheel to 4mm scale small shunting locomotives. The reason I ask is I am building a kit for someone and he wanted to know if I could fit a flywheel. I said that I could but, in my own opinion, it would be a waste of time and money.

 

My reasoning for this is that, even though the loco is large by industrial standards, the maxiumum diameter of flywheel would not be over 14mm and so couldn't store enough energy to be worthwhile after the resistance of the 6-coupled chassis and geartrain is considered, not to mention the weight of a train being hauled. But mainly because the loco will use an 80:1 gearbox and any energy that does overcome the resistances at a time of losing electrical pickup isn't going to last long anough to turn the wheels far enough to make any difference in crossing bad pickup spots, such as point frogs. Of course the time when you would most need to overcome bad pickup points etc. is when you are actually shunting, i.e. at low speed and at that time the flywheel is surely completely useless.

 

Or am I missing the point? Is there some other advantage to a flywheel on a shunting loco because a lot of people seem to fit them and I guess they must know something that I don't.

[28XX]

I suspect that even at 80:1 most model locomotive motors are used right at the bottom of their performance curves. Flywheels help to impove that situation, but ideally the higher the gearing the better.

 

The formula for inertia (I) includes radius squared, and the formula for kinetic energy of a flywheel includes omega (radial velocity)squared so you are right to cram as big a radius flywheel as possible to maximise its effect. Long thin flywheels are bad engineering.

Edited January 15, 2018 by 28XX

[chaz]

Advantages of a small flywheel are largely mythical - it just doesn't store enough energy to be significant. When I was a kid (when dinosaurs stilled roamed) there were such things as push-and-go toys. These were "charged up" by being repeatedly pushed forward very fast which span an internal flywheel so that the toy could then be released and shot across the carpet. But out models are not operated like that - are they?

 

A potential disadvantage, if the flywheel is not perfectly balanced, is that it might well cause vibration, noise and lead to increased wear in whatever bearings support it. Brian Clapperton (of ABC gearboxes - a 7mm resource) advises strongly against the use of flywheels.

 

"Real" flywheels - as distinct from those used in models - are designed with a diameter as large as possible or as practical and with most of their weight at the rim where it will have the most effect. So, good idea in a model loco? Almost certainly not.

 

HTH

 

Chaz

[cctransuk]

Advantages of a small flywheel are largely mythical - it just doesn't store enough energy to be significant. When I was a kid (when dinosaurs stilled roamed) there were such things as push-and-go toys. These were "charged up" by being repeatedly pushed forward very fast which span an internal flywheel so that the toy could then be released and shot across the carpet. But out models are not operated like that - are they?

 

A potential disadvantage, if the flywheel is not perfectly balanced, is that it might well cause vibration, noise and lead to increased wear in whatever bearings support it. Brian Clapperton (of ABC gearboxes - a 7mm resource) advises strongly against the use of flywheels.

 

"Real" flywheels - as distinct from those used in models - are designed with a diameter as large as possible or as practical and with most of their weight at the rim where it will have the most effect. So, good idea in a model loco? Almost certainly not.

 

HTH

 

Chaz

 

I fit flywheels whenever possible - I find that they prolong both acceleration and deceleration.

 

As an example; I am building an Impetus kit of PWM652 at present, which is fitted with one of my Mitsumi motors and a High Level gearbox.

 

I test ran it both without and with a flywheel - which is not of large diameter because of the width of the engine compartment.

 

It was indisputable that the overall control was far superior with the flywheel fitted.

 

Regards,

John Isherwood.

[Ruston]

I fit flywheels whenever possible - I find that they prolong both acceleration and deceleration.

 

As an example; I am building an Impetus kit of PWM652 at present, which is fitted with one of my Mitsumi motors and a High Level gearbox.

 

I test ran it both without and with a flywheel - which is not of large diameter because of the width of the engine compartment.

 

It was indisputable that the overall control was far superior with the flywheel fitted.

 

Regards,

John Isherwood.

I am interested how you can discern the superiority of the flywheel. I ran one of my own locos (Judith Edge Yorkshire DE2 with Mitsumi motor and HL Loloader 90:1 box) with and without a  (12mm) flywheel and I honestly could not see any difference.

Edited January 15, 2018 by Ruston

[DCB]

Hornby and Bachmann fit small flywheels so presumably they must have concluded they are beneficial.   I have a K's 57XX with quite a large flywheel which runs beautifully on indifferent track better than the latest Bachmann Pannier.   The big advantage of the flywheel is avoiding the braking effect of the motor when power is removed due to a worm drive so I would try to fit the largest solid flywheel possible.  Sculpting away the centre is a waste of useful weight  A bevel drive is much better than a worm for smooth running when contact is intermittent as it is reversible so the wheels can drive the motor and flywheel but with a bevel drive a flywheel is a liability and just over-stresses the gear train when the train stops suddenly.  The ideal is a  flywheel with a torque limiting clutch driving a bevel drive but I don't think anyone makes one commercially

[Horsetan]

...  A bevel drive is much better than a worm for smooth running when contact is intermittent as it is reversible so the wheels can drive the motor and flywheel but with a bevel drive a flywheel is a liability and just over-stresses the gear train when the train stops suddenly.  The ideal is a  flywheel with a torque limiting clutch driving a bevel drive but I don't think anyone makes one commercially

There hasn't been a decent bevel geartrain since the RG4 disappeared. I've tried Grandt Line's bevels and they are a touch rough.

 

Slaters produce some crossed helical boxes but I've never seen them used in 4mm scale even though they are apparently small enough.

 

There hasn't been a decent clutch system since Brimalm stopped making DynaDrive.

[cctransuk]

I am interested how you can discern the superiority of the flywheel. I ran one of my own locos (Judith Edge Yorkshire DE2 with Mitsumi motor and HL Loloader 90:1 box) with and without a  (12mm) flywheel and I honestly could not see any difference.

 

It's purely subjective - but if I spend money / time on buying / turning a flywheel, you can bet your last penny that I can see the improvement !!

 

Regards,

John Isherwood.

[Barry O]

There hasn't been a decent bevel geartrain since the RG4 disappeared. I've tried Grandt Line's bevels and they are a touch rough.

 

Slaters produce some crossed helical boxes but I've never seen them used in 4mm scale even though they are apparently small enough.

 

There hasn't been a decent clutch system since Brimalm stopped making DynaDrive.

Horsetan have you seen Mike Edges version

 

http://www.rmweb.co.uk/community/index.php?/topic/45248-judith-edge-kits/?p=3000154

 

the bevel gears are very cheap...bu they work really well....

 

baz

[micknich2003]

Wrote almost seventy years ago, but still revellant. Draw your own conclusions.

[uax6]

And we moan about not being able to buy a motor, Mr Jackson (that Mr Jackson?) had to make his own!

 

Andy G

[chaz]

It's purely subjective - but if I spend money / time on buying / turning a flywheel, you can bet your last penny that I can see the improvement !!

 

Regards,

John Isherwood.

 

 

Well John, your argument has some force but surely it needn't be "purely subjective". It should be possible to set up some tests that prove the efficacy or otherwise of flywheels in small models. An experiment consisting of running a loco fitted with a flywheel onto a dead section of track at various speeds and measuring at what point it stops and then repeating the test with the flywheel removed would have some merit.

 

Chaz

[cctransuk]

Well John, your argument has some force but surely it needn't be "purely subjective". It should be possible to set up some tests that prove the efficacy or otherwise of flywheels in small models. An experiment consisting of running a loco fitted with a flywheel onto a dead section of track at various speeds and measuring at what point it stops and then repeating the test with the flywheel removed would have some merit.

 

Chaz

 

No doubt - but I KNOW that the flywheels improve performance, and I feel not the slightest need to PROVE the fact.

 

Others can choose to accept or reject my views at their pleasure.

 

I'm a railway modeller, not a model test engineer!

 

Regards,

John Isherwood.

[GeoffAlan]

I tend to think that a flywheel is almost always worth fitting in OO. A number of my N gauge locos have one, factory fitted, and all of them run better on dirty track than similar non-flywheel models. The gains are small but all you need is to roll the wheels on a fraction of a turn in order to restore contact and power. 

[NIK]

Evening all,

 

I would like to know people's opinions on fitting a flywheel to 4mm scale small shunting locomotives. The reason I ask is I am building a kit for someone and he wanted to know if I could fit a flywheel. I said that I could but, in my own opinion, it would be a waste of time and money.

 

My reasoning for this is that, even though the loco is large by industrial standards, the maxiumum diameter of flywheel would not be over 14mm and so couldn't store enough energy to be worthwhile after the resistance of the 6-coupled chassis and geartrain is considered, not to mention the weight of a train being hauled. But mainly because the loco will use an 80:1 gearbox and any energy that does overcome the resistances at a time of losing electrical pickup isn't going to last long anough to turn the wheels far enough to make any difference in crossing bad pickup spots, such as point frogs. Of course the time when you would most need to overcome bad pickup points etc. is when you are actually shunting, i.e. at low speed and at that time the flywheel is surely completely useless.

 

Or am I missing the point? Is there some other advantage to a flywheel on a shunting loco because a lot of people seem to fit them and I guess they must know something that I don't.

 

Hi,

 

The energy stored in a flywheel is proportional to the rotational speed squared. Because there is an 80 to 1 gearbox the motor speed is still relatively high when shunting.

 

As to extra vibration due to eccentricity a small amount of vibration may crush minute debris on the rail tops possibly improving pick up and traction.

 

A coreless motor has an advantage in that it has no magnetic detents (detents cause friction) so the need for a flywheel is lessened.

 

Coreless motors may become more easy to get now that Ready to Run manufacturers are starting to use them.

 

I think someone in MERG is experimenting with a coreless motor and a large capacitor to give a flywheel effect (for DC).

 

If you happened to be using DCC then some decoders can have Stay Alive circuits attached. I think these are all based on capacitor energy storage. 

 

I'm not sure what the energy density is but capacitors can be hidden anywhere in a loco or even in a shunters truck or track circuit/barrier wagon.

 

 

Regards

 

Nick

[Ruston]

It's purely subjective - but if I spend money / time on buying / turning a flywheel, you can bet your last penny that I can see the improvement !!

 

Regards,

John Isherwood.

Have you also tried lubricating the gearbox with snake oil?

[AndyID]

Evening all,

 

I would like to know people's opinions on fitting a flywheel to 4mm scale small shunting locomotives. The reason I ask is I am building a kit for someone and he wanted to know if I could fit a flywheel. I said that I could but, in my own opinion, it would be a waste of time and money.

 

My reasoning for this is that, even though the loco is large by industrial standards, the maxiumum diameter of flywheel would not be over 14mm and so couldn't store enough energy to be worthwhile after the resistance of the 6-coupled chassis and geartrain is considered, not to mention the weight of a train being hauled. But mainly because the loco will use an 80:1 gearbox and any energy that does overcome the resistances at a time of losing electrical pickup isn't going to last long anough to turn the wheels far enough to make any difference in crossing bad pickup spots, such as point frogs. Of course the time when you would most need to overcome bad pickup points etc. is when you are actually shunting, i.e. at low speed and at that time the flywheel is surely completely useless.

 

Or am I missing the point? Is there some other advantage to a flywheel on a shunting loco because a lot of people seem to fit them and I guess they must know something that I don't.

 

High gear ratios produce lot of friction. You can get to a point where most of the power produced by the motor is overcoming friction in the gear-train rather than doing anything useful. The transmission is acting like a brake on the motor and if the power is cut to the motor it will stop almost immediately. For that reason a flywheel is probably a good idea with large ratios.

 

In my mucking about I've found that the best option is to use the largest diameter motor possible with the lowest gear ratio that will allow the motor to generate the required amount of torque. Funnily enough I've seen some pretty good results with ancient brass Tri-ang two-start worms driving nylon worm gears. The small gear ratio and brass/nylon combination even allows the worm-gear to "back-drive" the worm.

 

My current plan (if I ever get around to it) is to eliminate the low-speed shunting problem entirely by using battery powered radio-controlled shunters, but that's another story altogether.

[34theletterbetweenB&D]

No doubt - but I KNOW that the flywheels improve performance, and I feel not the slightest need to PROVE the fact. ..I'm a railway modeller, not a model test engineer!...

 While using DC I never had a shadow of doubt that flywheels were beneficial to the appearance of a slowly moving loco (subjective).

 

The performance testing background in so many aspects of my career required me to prove it, and it is easily done. The model already has a 'flywheel' in the form of the rotating mass of all the components on the motor shaft, so the comparison of 'without flywheel' and 'with flywheel' also provides a useful rule of thumb for the scale of added rotating mass and increased diameter over the armature likely to be required.

 

All you need is a length of track - ideally straight and level - with an isolating break in one rail, and a controller connected at a fixed setting, which is not touched for the trial duration. Start loco from same point every time, measure stop point after isolating break. Repeat ten times for the 'without flywheel' condition and if performance is decently stable (results within +/- 5% of the mean) proceed to repeat in 'with flywheel' condition, and compare means of both sets of recordings. (If performance isn't stable, get to work on the mechanism to iron out the cause of instability.)

 

If you can roughly double the mass of an armature by adding a flywheel, and get most of that flywheel mass placed at 50% greater diameter than the armature maximum diameter, there will be easily observed subjective improvement in movement.

 

Side note. The various flywheel drives found in D+E traction are worth characterising for repeat performance stability by the method described. These drives are a little 'cryptic' due to the combination of decent sized motor and big flywheel(s) smoothing their running performance. But if the repeat perfomance is not stable, then there's room for significant improvement.

[chaz]

No doubt - but I KNOW that the flywheels improve performance, and I feel not the slightest need to PROVE the fact.

 

Others can choose to accept or reject my views at their pleasure.

 

I'm a railway modeller, not a model test engineer!

 

Regards,

John Isherwood.

 

 

Point taken.

 

Incidentally none of my own kit built O gauge models have flywheels, but they all have ABC helical gearboxes, which unlike worm drives can be back-driven. In fact with Maxon motors the locos can be pushed along the track with gentle pressure on the buffers. This avoids the instant braking effect of a worm drive and probably negates the need for a flywheel.

 

ATB

 

Chaz

[cactustrain]

Locomotive wheels act like flywheels. A larger size of wheels and the number coupled together adds to the effect because of the greater mass involved. Perhaps flywheels aren't needed in an O gauge locomotive, but I think they are in an OO gauge shunting loco. I have to agree that the balancing and the quality of the bearings in the motor have to be up to the job.

[AndyID]

which unlike worm drives can be back-driven.

 

Hi Chaz,

 

Worm drives can be back-driven. The reason they usually won't back drive is because of very large reduction ratios create a lot of friction, but if you use a two or three start worm to produce a smaller reduction ratio they will back drive.

 

A worm drive is really just a particular form of helical drive anyway

 

Andy

[Ruston]

Locomotive wheels act like flywheels. A larger size of wheels and the number coupled together adds to the effect because of the greater mass involved. Perhaps flywheels aren't needed in an O gauge locomotive, but I think they are in an OO gauge shunting loco. I have to agree that the balancing and the quality of the bearings in the motor have to be up to the job.

In an actual live steam locomotive, maybe, but most model locomotives, especially in the smaller scales, such as OO, use an electric motor with a worm in the geartrain, which means any flywheel effect you might get from the wheels cannot be transferred back to the motor, no matter what the size or number of the wheels. The motor drives the wheels, not the other way around. You've only to  try pushing a loco with a worm drive along the track to see this.

 

The only way the wheels can possibly act as a flywheel is with a geartrain that is free to be powered by the wheels, such as a bevel drive, or helical gear.

[cactustrain]

In an actual live steam locomotive, maybe, but most model locomotives, especially in the smaller scales, such as OO, use an electric motor with a worm in the geartrain, which means any flywheel effect you might get from the wheels cannot be transferred back to the motor, no matter what the size or number of the wheels. The motor drives the wheels, not the other way around. You've only to  try pushing a loco with a worm drive along the track to see this.

 

The only way the wheels can possibly act as a flywheel is with a geartrain that is free to be powered by the wheels, such as a bevel drive, or helical gear.

That's interesting. You may well be right in what you say. Another question springs to mind though. Will a worm driven locomotive that weighs more take longer to stop when the power source is removed when travelling on the flat at a given speed?

[hayfield]

I have a couple of locos with flywheels and for what ever reason they do run better than those without

 

I also have a Bemo loco which has a faultless in built electronic flywheel system using an old  standard controller (H&M), no idea how it works though, but the chassis is very heavy and fills the body

[GeoffAlan]

My N gauge flywheel models run on from a scale 45mph after power is abruptly cut. That tells me the flywheel is having an effect.