Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!

Flywheels: a Topic Revisited - with a Restriction

6 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    December 2010
  • From: Portland, Oregon
  • 630 posts
Flywheels: a Topic Revisited - with a Restriction
Posted by Attuvian on Thursday, June 6, 2019 12:15 AM

I've read a number of strings on this forum regarding flywheels.  Many of them quickly take on a DCC perspective, especially where back-EMF decoders are in use.  Also, as with many discussions here, there is a significant amount speculation, personal preference, and other subjective issues that are injected.  Not that such are entirely useless, but they do muddy the water somewhat.

May I attempt to revisit the matter of flywheels on a restricted basis, specifically considering them solely from a DC use perspective.

It is apparent that the major motor liability that flywheels were designed to overcome is the gogging of older armatures, an issue that results primarily in jerkiness in low speed operations.  Where older motors are still in DC use flywheels still mitigate this issue - as well as provide momentum in momentary loss of voltage due to trackage matters.  But the motors of this generation are skew-wound, to address and eliminate at least the cogging.

But I note that even with the older motors that were not skew-wound, there was quite a bit of variation in the size and mass of the stock flywheels that were affixed to them (e.g., in old Athearn Blue Box locos).  In those BBs alone, some engines had substantially larger flywheels that others.

So here's my question: what were the determining factors that governed the size of the flywheels fitted to a particular motor?  In most cases it doesn't seem that it was a simple matter of space available.  Was it due to differences in the electrical characteristics of a particular motor?  If not, was it a case of smaller ones being sufficient for the need but bigger must certainly be better?  As for Athearn, there are lots of different part numbers for BB motors, but in many if not most cases the dimensions of the motor casings are identical, only the size of the flywheels (and perhaps the style of their fittings) are different.  I'm just guessing that those similar casings house electrically similar guts.  

You will likely be asking just why I am asking.  Well, I've got more than one size of them under the shells of some on my roster, and I wonder if it's worth the fuss to change out the smaller ones.  I am asking this strictly in regard to DC operation of older engines (some of which, admittedly, do not have Athearn motors).  I'm trying to keep this somewhat general as I don't want to have to list specific models and post photos!

Jump in, please.  Just leave the DCC and decoder stuff out.  If you can, that is.  And, yeah, I could just get rid of these oldies.  'Cept I'm too old, too nostalgic, and too cheap! 



  • Member since
    April 2013
  • 906 posts
Posted by Southgate on Thursday, June 6, 2019 12:39 AM

I run DC only. I have added flywheels to a number of locos strictly for the added momentum and smoothing of the mechanisms. For comparitive purposes, a Keystone 44 tonner that came with a sagami can motor and NWSL gears ran more than reasonably smoothly. I added as large of flywheels, 2 of them, as space would allow. Now it runs superlatively smoothly.

I remotored and regeared an Athearn hustler with a Sagami can, and modified the axles to accept Atlas (Austria) gears, and used Atlas worms on the shafts. Ran well, but the addition again of as large of flywheels as would fit, it runs extremely smooth.

And, I just had to try this: Put as large a coreless can motor as would fit in a Tyco Chatanooga Choo Choo, and a huge flywheel. All in the boiler area, not tender drive now.  I modified Athearn and Kato gears to it's drivers. It runs quite smoothly as far as taming radical speed variations, but has a little wobble from drivers side play. (I got a deal on motor, BTW)

The smoothest locomotives I have ever seen run are my unmodified Atlas Alco RS and RSDs, and they have generous machined flywheels.

I have a couple WIP small 4 wheel switchers in the process of being built. The adding of flywheels or not was the deal breaker. They do have flywheels, and they run great as a direct result of them.

And, allow me please, my favorite flywheel assist: An MDC 2-6-0 chassis converted to a 4-4-0, boiler structure from a Tyco "Dixie" 4-6-0 (shortened), a Sagami can, and a flywheel that makes this locomotive run as smooth as silk, with an amazing amount of momentum.

I am a huge believer in flywheels to smooth out running quality, and the bigger the better. (Having a Sherline lathe makes all these custom flywheels possible)

And I will add, this is not to compensate for poor quality motors or intermittent power pick-up, it is to augment already good motors, gears, and clean power pick-up. Dan


  • Member since
    January 2004
  • From: Canada, eh?
  • 10,490 posts
Posted by doctorwayne on Thursday, June 6, 2019 2:12 AM

I'm also a DC operator, and when I was still using diesels, the only ones which seemed to have flywheels of any consequence were the old Model Power E-units.  They ran smoothly enough for my tastes, and I never really had any issues with their performance, either in their running qualities or their pulling power.
I also had a number of Athearn diesels, all factory-equipped with flywheels.  While they were decent runners and pullers, when I replaced the motors with better quality can motors, I also eliminated the flywheels, using the newly available space for additional weight.  I found the smoothness of the running qualities better than the original versions, as the electrical pick-up was more reliable due to the added weight, and the pulling power was greatly improved - a consideration more important to me than coasting ability, especially as my layout is mostly curves and grades, the latter often long and at around 2.8%.

When I back-dated my layout to the late '30s, the diesels were mostly sold-off, although a few favourites are in a display cabinet.

I've had only one steamer with a flywheel, a Proto USRA 0-8-0.  It was an early version with no tender pick-ups, and was capable of pulling only 3 or 4 cars up a grade in the town to which I had planned to assign it.  I was on the verge of getting rid of it, but decided to pull it apart to see if there was any room inside to add some weight.
What I found was a circuit board for the headlight (not needed for daytime operation in my era) and a tiny flywheel on the motor shaft.  Both were removed and all available space thus created in the boiler was filled with lead.  The pulling power was greatly increased, and when I re-detailed the loco (all of the piping on these and other Proto steam locomotives was undersize, probably due to the die cutters not understanding that pipe dimensions refer to inside diameters, not the outside diameters) I was able to add even more weight to the loco externally.

None of my other steamers were equipped with flywheels, but all received additional weight, properly balanced at the mid-point of the driver wheelbase.  All are smooth runners, and all are decent pullers, and regardless of size or make, any will run in combination with any others, regardless of where they might be placed within the train.

I also have some steam locomotives still equipped with open-frame motors, and most of those have had the original magnets replaced with the rare earth-type magnets.  This lowers current draw (never really a concern for me), but also allows them to start and run at lower speeds, and they definitely pull more, too.

I have no complaints about the performance of any of these locomotives, but my priority is having locomotives which are capable of moving the trains to which they're assigned.  I can't claim that they're as smooth-running as those of someone who favours flywheels (maybe they are, maybe they aren't), but that's not my primary concern.

As for electrical pick-up, most of the plastic steamers came with all-wheel pick-up, and the brass and diecast locos which I have in service have been retrofitted with it.
Unless I've been working in the layout room, doing tasks that creates dust, I don't clean track except after ballasting or adding scenery near tracks.  With normal operations, track cleaning is done with a shop vac, usually once every year or two.


  • Member since
    August 2011
  • From: A Comfy Cave, New Zealand
  • 4,129 posts
Posted by "JaBear" on Thursday, June 6, 2019 2:37 AM

...and I wonder if it's worth the fuss to change out the smaller ones. 

Gidday John. No! (unless you're totally bored, and have no further model railroading goals!)

Cowboy Cheers, The Bear.Pirate

"One difference between pessimists and optimists is that while pessimists are more often right, optimists have far more fun."

  • Member since
    December 2010
  • From: Portland, Oregon
  • 630 posts
Posted by Attuvian on Thursday, June 6, 2019 11:10 AM

...and I wonder if it's worth the fuss to change out the smaller ones. 

Gidday John. No! (unless you're totally bored, and have no further model railroading goals!)

Cowboy Cheers, The Bear.Pirate


And a gidday to you, Bear.
Your "No!" carries a good deal of weight.  If only because I have no excess time, shortage of projects and goals, or boredom in any realm of retirement.  My posting was the fruit of a late-night mental meandering that occurred on successive days, a sure alert to the need for the stabilizing thoughts and opinions of friends far and wide (for which you qualify nicely)!
Smile, Wink & Grin
BTW, I note with amusement that, in spite of my wish to avoid expanding the discussion to issues of electronics and DCC, it has been moved to this particular forum. Hope that doesn't blow out the candle just after it was lit . . .
  • Member since
    January 2009
  • 4,811 posts
Posted by RR_Mel on Thursday, June 6, 2019 1:59 PM

I don’t think it makes any difference when they move things around, they move most of my post to DCC even when they don’t come close.
I think all the newer locomotives, say 80s on, don’t need flywheels.  I operate about 70% DC mode and I can’t tell the difference between a locomotive with a flywheel and one without.  The early locomotives with non skewed armatures probably need them.  I have replaced my older non skewed motors with can motors with the exception of my two old MDC 0-6-0s and they both run great without flywheels.
I think that early on before Nickel Silver rails flywheels were more for momentum because of poor track to wheel contact.  The older iron and brass rails were harder to keep clean than NS rails because of rust and corrosion.
If my locomotives had flywheels before I replaced the motor I kept them, I haven’t added any flywheels to any of my locomotives.  It’s much easier to keep the flywheels than do a mod to replace the void where the flywheel was.
I’m not into momentum when running my trains, all of my DC power packs have switchable momentum all in the off position.
My Model Railroad   
Bakersfield, California
I'm beginning to realize that aging is not for wimps.
  • Member since
    February 2002
  • From: Reading, PA
  • 27,977 posts
Posted by rrinker on Thursday, June 6, 2019 1:59 PM

 As for what decided how big a flywheel to put in the locos from the factory - size and cost. I highly doubt any of the mass manufacturers actually did any studies to say "hey, we need a flywheel of X mass to make this loco run the best". Withness the absolutely useless (lead or pot metal) flywheel MDC added to later runs of the boxcab diesel. It's so small in diameter and so light, not to mention the added friction of the drive shaft to it, that it probably makes the things run WORSE not better. It's also not exactly balanced - by "not exactly" I mean "not at all"

 There are two factors in the energy storage of a flywheel - the mass of it, and the speed. I recall an article on improving the mentioend MDC boxcab that involved using a better quality brass flywheel and another set of gears to make the flywheel turn faster. 

 Also, may older motors had much higher rotating mass in the armature, which also adds to the flywheel effect. 

 I remember at the old club I belonged to, someone picked up some E units, I think they were the Rivarossi shells but they had the Model Power drives, although one of them had been remotored with a HUGE can motor, the motor was the diameter of the flywheels. Might have even been a coreless motor - it was definitely an expensive motor, not some cheap toy motor, worth what the guy paid for BOTH locos alone. That loco was amazingly smooth, and woudl coast for a long way after power was cut because of the huge flywheel. At the same time, I have some of the Stewart/Bowser Baldwin switchers, they are small locos so the flywheels are rather small, but they do have top quality Canon motors. On DC, they will coast a good long way from full throttle after power is disconnected. The flywheels and motor can't account for that along, the high quality driveline components help a lot.

 I'm not so sure this post belongs in electronics/dcc - it's a mechanical topic. But I think as soon as the acronyms DC or DCC appear in a post, the thread gets moved here. Seems like this section is a catch all for most anything technical, even if it doesn't involve anythign electrical or electronic. It's not scenery, it's not track laying, it's not layout design....



Modeling the Reading Railroad in the 1950's


Visit my web site at for construction updates, DCC Info, and more.

Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!

Users Online

Search the Community

Model Railroader Newsletter See all
Sign up for our FREE e-newsletter and get model railroad news in your inbox!