RTR Small Shunting Engines, Flywheels, and DCC Stay Alives

[Ruston]

 Rather than derail the particular subject of the Rapido Y7, perhaps it's better to open a new discussion here?

 

2 hours ago, Mark Dickerson said:

For me, it'll always be mechanism first, I prefer the idea of a flywheel and the DCC and sound stuff can - er - go whistle

What is it about a flywheel? I don't get why people think they're worth having in such small models. The flywheel that can be got into this Y7, or the Dapol HL, isn't likely to weigh much more than 10-15g and as these small shunting engines are only going to be running at low speeds there isn't enough energy stored in the flywheel to keep the wheels turning in the event of a momentary loss of power due to dirt or a bad track joint. On the other hand, a decent Stay Alive will keep the motor going for several seconds, up to six inches, even with the loco down to a crawl.

 

OK, I get that some people will never be convinced about DCC, which is their loss, and I don't expect a manufacturer to fit a SA in every model, including those that are going to DC purchasers (although some do fit speakers that will never be used), but it would be nice for a manufacturer to get with the 21st Century and at least provide space for a SA, and tell us that such a space is already designed in, instead of us having to wait until we get our hands on a model and work out if one can be fitted, not to mention to then have the need to hack lumps out of the chassis or bodywork to fit one ourselves.

 

Small shunting engines, due to their light weight, low speeds and short wheelbases, are the ones more than any that can gain the most benefit from a Stay Alive but they are still not being catered for by RTR manufacturers, who are still wedded to fitting a useless lump of turned brass to the end of the motor. Stay Alives have been around for a while now; they're not some brand-new technology that no one is yet using. They are, to my mind, the greatest gain to be had from DCC, but none of the industrial offerings from Hornby or Hattons have had provision for a Stay Alive, nor would it seem have those now in the pipeline from Dapol or Rapido. Isn't it time in new projects at least that they did?

[Izzy]

I agree with a lot of what you say but I believe flywheels are used mainly to 'tame' small frisky motors. That's certainly the effect they will have at low rpm, a constant load to dampen down the speed, and for those on DC might make a considerable difference, especially if the gearing isn't very high.

[Mark Dickerson]

But is a stay alive that works for several seconds useful for shunting? Isn't the pointless space in a shunting loco a pre-installed speaker? There's your space.

[The Johnster]

I used to be in thrall to the flywheel gods and the matter seemed simple for me; flywheel good no flywheel not good.  But it’s not as simple as that.  For a DC train running at a reasonable speed a flywheel is A Good Thing, which will enable smoother running and much smoother acceleration and deceleration, and should provide smoother starting and stopping. 
 

But a DC shunting engine, especially a small one, working at low speeds and stopping to change direction frequently, has all the cards stacked against it.  The voltage is low and resistance from dirt or poorly laid track high as a proportion of the loco’s  momentum, as is any friction from gears and drag from pickups or fouling motion.  A flywheel sounds like a cure-all for these problems, but the size of the loco means that only a very small one can be shoehorned in, so the beneficial effects, if there are any, will be very limited.   In such locos, the space is usually better used to accommodate more ballast over the driving wheels, which will give the loco more momentum and aid pickup.  
 

DCC has a distinct advantage in this situation; there is always 12vdc available at the rails and an onboard stayalive can be used.  I’d regard one as essential for DCC shunting engines and reckon that flywheels should not be considered until after a stayalive is provided, and if anyone ever devises a stayalive for DC use, I’d say the same thing for it.  I can’t escape the feelng that, for some RTR models, flywheels are provided as a selling point because they infer a level of ‘proper engineering’ rather than for any objectively quantifiable benefit!

 

DC, all I can afford and likely to remain my method of control until my lottery jackpot comes in, is capable of providing smooth and reliable running of small engines with or without flywheels so long as the following conditions are satisfied:-

 

1) Track is laid level and smoothly to the adjoining piece, and any turnouts are kept away from changes in gradient.  
 

2) Loco mechs are of good manufacturing quality, free-running, and correctly lubricated (and it is surprising how often they aren’t, though most more recent products usually pass muster)

 

3) An effective and rigorous hygiene regime is in place; railheads, turnout closure locations, wheels (rail contact and tyre back pickup contact) and pickups.  
 

4) Back to backs are consistent and chassis square and level. 
 

5) There are no obstructions; sounds obvious but check crud in flangeways or between turnout blade and closure rails, and small grey-brown camouflaged bits of debris on rails.  
 

That said, I’d like to see higher gear ratios for locos that do not require to be run at speed; control would be easier and running smoother.  This would be preferable to flywheels IMHO.  

[JohnR]

11 hours ago, Mark Dickerson said:

But is a stay alive that works for several seconds useful for shunting? Isn't the pointless space in a shunting loco a pre-installed speaker? There's your space.

 

But the thing is, you need a say alive more if you have DCC sound. A flywheel maybe able to get the loco to "coast" over the dead spot, but a momentary drop in electrical contact will interupt the sound, which can have quite a jarring effect when it restarts.

[Michael Hodgson]

3 hours ago, JohnR said:

 

But the thing is, you need a say alive more if you have DCC sound. A flywheel maybe able to get the loco to "coast" over the dead spot, but a momentary drop in electrical contact will interupt the sound, which can have quite a jarring effect when it restarts.

Yes, but we don't all fit sound.  Some are DC (without sound).  Some choose DCC without sound to keep the cost down or because they're not convinced by the noises they make.  An 0-4-0T can only have 4 pickups at best, so is more prone to dropouts due to dirt etc than anything with at least 6 wheels, so flywheels and stay-alives are more beneficial on those locos which have least room to fit them.  If there is space for a flywheel or a stay alive but not both, more likely to be the case in a small loco than a big one, it makes sense to desgin to allow either according to user's preference.

 

[Steven B]

Keep alives are effectively an electrical version of physical flywheel in small models and work on DC:

(Ignore the sound-track, it's been over dubbed with the real thing!)

 

 

Steven B.

[BernardTPM]

9 hours ago, The Johnster said:

I’d regard one as essential for DCC shunting engines and reckon that flywheels should not be considered until after a stayalive is provided, and if anyone ever devises a stayalive for DC use, I’d say the same thing for it.

There was an RM article back in, I think, the 1980s where someone fitted a large capacitor to a Lima Cl.33, dubbing it an electronic flywheel.

[Ruston]

16 hours ago, Mark Dickerson said:

But is a stay alive that works for several seconds useful for shunting? Isn't the pointless space in a shunting loco a pre-installed speaker? There's your space.

It is very useful for shunting. That's when it's at its most useful. When you run, say a main line express, it's got lots of wheels for pick up and it's going fast enough to not stall on dirt or a bad joint, which would stall something with fewer wheels and is travelling slowly. When I say that it works for several seconds, that's the maximum but if power is lost for only a fraction of a second the SA only discharges its stored electrical energy for that fraction of a second. As soon as the wheels are picking up again the SA is recharging and the motor is running from the power that comes from the rails.

 

The space for a speaker isn't pointless if you intend to fit sound, which the manufacturers are now providing for. I don't know about the Rapido Y7 but the Dapol Hawthorn, Leslie is being offered with a factory sound fit. Besides, a speaker is usually quite flat but none of the good SAs are of the same shape or dimensions.

 

16 hours ago, Izzy said:

I agree with a lot of what you say but I believe flywheels are used mainly to 'tame' small frisky motors. That's certainly the effect they will have at low rpm, a constant load to dampen down the speed, and for those on DC might make a considerable difference, especially if the gearing isn't very high.

Isn't this old-fashioned thinking? From the days of open-frame, 3-pole motors and all that? The models we are discussing do have high gearing. None of the Hornby industrials have flywheels and they all run very smoothly with what must be the smallest motors to be fitted to 4mm scale RTR. It's the new projects from other manufacturers that seem to be designing flywheels in and this is what I'm getting it at. Design in space for a Stay Alive, not a flywheel as the flywheel adds nothing in this type of loco. Make the space so a SA can be fitted by those who want one and those who don't can fill the space with lead to gain extra traction.

 

For anyone who doubts what a Stay Alive can do at very low speeds. If you have track as bad or as dirty as when it's removed from the rails then you have a problem that nothing will fix. The motor would have been turning at such a low speed that no flywheel that could ever be fitted in there would have the slightest effect in any way at all.

 

 

 

Edited November 28, 2022 by Ruston

[D9020 Nimbus]

I don't know whether Rapido are planning a sound-fitted model, but if they are, then it needs to have a stay-alive. I have four sound fitted 0-6-0s and only the Bachmann Caley 0-6-0 is truly satisfactory — and no doubt it has pick-ups on the tender. The Hornby 08 with Loksound chip I have — purchased about 10 years ago — is inclined to have sound stop and start on crossing a dead-frog point — though it crosses the point at walking pace without sound turned on.

 

An 0-4-0 would be even worse. I'll be buying the Y7 anyway, but not a sound-fitted version unless a stay-alive is fitted.

[The Johnster]

4 hours ago, BernardTPM said:

There was an RM article back in, I think, the 1980s where someone fitted a large capacitor to a Lima Cl.33, dubbing it an electronic flywheel.

I attempted something like that at around that time, the guinea pig being a Lima 4575 which refused to run slowly and smoothly at the same time.  You can do it easily enough if the loco is to run in one direction around a tailchaser layout, but it defeated my attempts when I required the loco to run the other way, which is of course essential on a terminus layout and would be an absolute necessity for me on any layout; I like to shunt!

 

If you place the capacitors (you need one for each polarity) in line on the pickup-motor feed wires, you prevent current being passed ‘back’ to the rail, and your loco will not move.  When you reverse polarity the same thing happens (no sh*t, Sherlock). Ok, try them across the motor terminals; no dice.   Across feed wires; dead short.  From feed wire to opposite motor terminal; dead short.  Unidirectional; no power in other direction. 
 

What I think is needed is on-loco switching of both caps by some form of NFC or even infrared, and bypass wiring around the ‘return side’ cap while the bypass for the ‘feed side’ cap is switched out, routing the current from the feed rail through the feed side cap, then through the motor, returning through the return side bypass wire to the return side rail.  
 

Now, that was 40 years ago and there may be different products on the market now that can cope with reversing the polarity in DC configuration, but I am not much ‘into’ electronics and am unaware of them;  I sort of assume that if it could be done somebody would have done it, but ‘it ain’ ne’sarily so’; the widespread adoption of DCC by those who can afford it may mean that nobody’s tried; you want a stayalive, get DCC.  

 

In fact the advent of DCC forty years or so ago has effectively stifled any advance in DC control technology beyond the recent Bluetooth phone apps.  State of the art is still the GM HH; good, not complaining about it, but surely not the best that CAN be done.  
 

If anyone has any suggestions as to how stayalive night be achieved in DC, especially in very small locos, I’d be interested.  I’m not unhappy with the slow running of locos on my layout (I regard my Hornby Pecketts as borderline miraculous), but would always be interested in improving it.  I’m not convinced of the efficacy of mechanical flywheels on smaller locos though they do no harm on my Hornby 42xx or 5101.  

Edited November 28, 2022 by The Johnster

[Izzy]

3 hours ago, Ruston said:

Isn't this old-fashioned thinking? From the days of open-frame, 3-pole motors and all that? The models we are discussing do have high gearing.

 

Maybe, but I was simply replying to your query as to why makers still fit flywheels, what the reasons might be. Certainly with coreless motors, which of course have no native rotating mass, a flywheel will help dampen their sometimes frisky nature, when they have the power and size to be so given the very small ones sometimes now being used.

[Barclay]

My experience is not with R-T-R but for what it's worth I still use a flywheel whenever I can fit one in. In my case I'm not worried about the loco stalling but I do think that a flywheel gives a silkier, or smoother throttle response, and at least partly replicates the impression of something really heavy on the move. You only see visible run-on or momentum where you use a large flywheel, such as in this Nasmyth Wilson 0-8-0, or when the motor is fast-revving, like this small diesel shunter. Some of my American diesels have enormous flywheels and have very lengthy run-on. Other loco's with slower motors and small flywheels don't have a visible effect but I still think there must be some small benefit. Stay-alives are great of course especially where sound is involved, but I still believe in mechanical momentum!

 

 

[The Johnster]

'Something heavy on the move' (difficult to reproduce convincingly in smaller scales because of course speed and mass do not scale down in a linear way, compensation helps but is beyond my skill level), the impression of momentum and unstoppability conveyed by a train moving at even a slow speed.  I do my best with ballasting of vehicles and smooth, flat tracklaying to avoid sudden jerkiness, but it's imperfect at best; 7mm seems to be able to pull it off to a better extent though. 

 

I get there sometimes, though; last night I was watching a propelling movement of loaded (fully with real coal, accept no substitutes) minerals through some pointwork which was progressing nicely, smooth and slow at an even speed with a Baccy 56xx plodding along at the rear of it, with my eyes down at 4mm human eyeball level; very satisfying, even the wheel beats were right, I could have been at Radyr yard in 1960!

Edited November 30, 2022 by The Johnster

[Phil Bullock]

Is there confusion between the role of a flywheel and a stay alive? 

 

A flywheel on a DC loco will provide momentum but this will decay due to friction once the controller sends a voltage lower than required for maintenance of the current speed of the motor theoretically resulting in over-run when stopping (but probably minimal). 

 

A DCC stay alive does just that…. It keeps the chip alive at the last speed setting until the chip receives a DCC command telling it to change speed - until the capacitor is exhausted. This means that as long as any break in power is intermittent the driving characteristics of a loco should not change …. It still obeys DCC commands and will not over-run as long as it has track power. 
 

So despite the use of confusing terminology in some instances a stay alive isn’t a Dcc fly wheel and should not adversely affect slow speed shunting manoeuvres.

[Bucoops]

Having just bought my first gearbox with spur/helical gears I wonder if perhaps that should be the norm for very small locos as they allow the locomotive momentum to keep the motor turning with no power - whereas a worm of course stops solid. Turning the motor obviously makes it act as a dynamo so there would be a load introduced as a result, but it has to be better than worm drive?

[Mark Dickerson]

What was the gearbox and (perhaps to the point), roughly how much was it? Is it cost rather than convention why they're not as common?

[Bucoops]

1 hour ago, Mark Dickerson said:

What was the gearbox and (perhaps to the point), roughly how much was it? Is it cost rather than convention why they're not as common?

 

This particular one is for O gauge so would be a tad big. It was £130 including a Maxon motor - helical gears cost more to cut of course.

 

I believe DJH sell ones suitable for OO - but there may be a gap in the market for ones small enough for the locos in mind.

 

[rapidoTom]

Hopefully I can add a bit of a manufacturer perspective to this debate! Apologies if I re-iterate points from earlier posts but I'm just going through my thought process.

 

Flywheels add angular momentum to the motor, which adds inertia to the loco and helps over momentary disruptions in track power, and they do this on both DC and DCC tracks. Even a small one can multiply the momentum of the motor by several times, particularly with the coreless motors we use (coreless motors have several advantages, but rotational mass is not one of them!). That could take the roll-on time at a crawl speed from, say, 50ms to 250ms, which doesn't sound much, but is more than adequate for minor dust/dirt on reasonably well-maintained track. Conversely, stay-alives don't add inertia, they only help over dead track, and only on DCC - so if we have to pick one system to put in RTR locos, we have to pick the one that benefits everyone. It's just the realities of having to serve the wider market. Ideally, of course, we'd have both!

 

However, on DC, a stay alive isn't simple due to the electronics (most large capacitors are polarised) and potentially you lose some of the benefits if you have a PWM controller. So we don't factory-fit stay-alives, although reserving space for one is something we could look into. Unfortunately, there is no standard size (DCC decoders are easier as they have standard dimensions), so I wonder if that's something the NRMA or another society would be interested in specifying. The cost of a flywheel is fairly minimal (I know they seem expensive for kitbuilds, but when you make a few thousand locomotives, the economies of scale kick in) so there's no real downside to having one in my view.

 

On the use of worm gears over full spur/helical gearboxes, worms are not chosen so much for efficiency as for practicality. Firstly, they are effectively a one-tooth gear, so you can pack a high ratio into a small space without having to use low modulus gears, which need to be cut very precisely and are therefore expensive. Secondly they turn the drive axis 90°, so that on most locos, you can put the motor in line with the boiler, otherwise you have to have a very short (and thus less powerful) motor if it's across the footplate. Or a Ringfield/pancake type motor... engineering is usually a compromise!

 

Everyone's opinions will always differ, even within Rapido, but we think we've hit the right middle ground with this kind of chassis design. If I get an equal amount of complaints from all sides, we've probably done our job right!

[Flying Pig]

1 hour ago, rapidoTom said:

coreless motors have several advantages

 

Could you please expound a bit on those advantages?  I mean, apart from entertaining onlookers by the rage they provoke in some quarters.

[Ruston]

2 hours ago, rapidoTom said:

Hopefully I can add a bit of a manufacturer perspective to this debate! Apologies if I re-iterate points from earlier posts but I'm just going through my thought process.

 

Flywheels add angular momentum to the motor, which adds inertia to the loco and helps over momentary disruptions in track power, and they do this on both DC and DCC tracks. Even a small one can multiply the momentum of the motor by several times, particularly with the coreless motors we use (coreless motors have several advantages, but rotational mass is not one of them!). That could take the roll-on time at a crawl speed from, say, 50ms to 250ms, which doesn't sound much, but is more than adequate for minor dust/dirt on reasonably well-maintained track. Conversely, stay-alives don't add inertia, they only help over dead track, and only on DCC - so if we have to pick one system to put in RTR locos, we have to pick the one that benefits everyone. It's just the realities of having to serve the wider market. Ideally, of course, we'd have both!

 

However, on DC, a stay alive isn't simple due to the electronics (most large capacitors are polarised) and potentially you lose some of the benefits if you have a PWM controller. So we don't factory-fit stay-alives, although reserving space for one is something we could look into. Unfortunately, there is no standard size (DCC decoders are easier as they have standard dimensions), so I wonder if that's something the NRMA or another society would be interested in specifying. The cost of a flywheel is fairly minimal (I know they seem expensive for kitbuilds, but when you make a few thousand locomotives, the economies of scale kick in) so there's no real downside to having one in my view.

 

 

Thank You for the reply, Tom.

 

As I said, I don't expect a manufacturer to fit the SA but rather to make space available when designing the model and to make it known that it has been catered for so that we're not buying blind and hoping that one can be somehow fitted, usually after much chopping and changing of the model's innards. The SA that I use are the Lais Kungfu 871007, which measures 13x9x9mm (not including the shrink wrap), which is quite small for the performance it gives. I have found ways to install them in Hattons Barclays and Hornby's W4 Peckett, but it's not easy (milling the chassis block on the Barclay and replacing the motor, turning the motor through 90 degrees and refitting it using Araldite on the Peckett) and certainly voids the warranty, which although it doesn't bother me, I'm sure that it puts a lot of people off fitting one.

 

 

[SHMD]

1 hour ago, Flying Pig said:

 

Could you please expound a bit on those advantages?  I mean, apart from entertaining onlookers by the rage they provoke in some quarters.

 

I can answer some...

 

Advantages of the Coreless DC Motor: -

 

Light weight
cheap
very small sizes available
fast response
Low current
Highly efficient
no cogging effect
no quiescent magnetic field when unpowered
proven technology
no exotic materials in its construction
 

 

Note that not all these advantages apply to out particular application of small scale model railways.

 

 

Kev.

[Flying Pig]

2 minutes ago, SHMD said:

fast response

 

Given the subject of this thread that is perhaps not an advantage in this context.

[The Johnster]

Thank you for the highly illuminating manufacturers’ perspective, Rapido Tom; it does no harm to be reminded that a manufacturer needs to keep everybody happy, whereas I only need to keep me happy…

[rapidoTom]

Just to add a bit more background to the coreless motor explanation - in an iron core motor, 3 or more coils are wound around an iron core, which makes the rotating assembly fairly heavy. In a coreless motor, the coils are self-supporting so there is no heavy iron core. Because it doesn't have poles in the same way, you don't get the cogging effect when the poles and magnets line up, so it appears a bit smoother at low speed (if you see "5-pole" or "skew-wound" in the description of a motor, these are ways of mitigating the cogging effect in an iron core motor). 

 

It also means the motor is more efficient, so you can fit more power into the same space, useful in something like a Y7 with a very narrow boiler! They're usually quieter and have more linear control than the equivalent powered iron core motor.

 

If I was a marketing person, I'd probably leave it there, but there are a couple of downsides! They have to be made more precisely, so tend to be a little more expensive, and they don't dissipate heat quite so well, so if you like to run your locos at 100% throttle for hours on end, they're probably not the right choice for you. And of course the inertia is lower, so we like to add a flywheel to help make up for it.

 

Iron core motors are by no means bad, I use them in most of my kitbuilds to keep my costs down. But in our experience for a similar cost, coreless motors are better suited to RTR locos, particularly small shunters.

 

Thanks for the stay-alive info @Ruston, I'll have a look at the Y7 CAD and see how it compares. We've got plenty of market research into the proportion of people using DC, DCC, sound etc. but I can't remember if that included stay-alives in the surveys - I might see if our social media team can gather some info on that.

Edited December 7, 2022 by rapidoTom