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Flywheels & DCC?

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Posted by Train Modeler on Sunday, November 16, 2014 7:18 AM

Take a motor without flywheels and remove power, see how long it continues to turn.  Do the same with a motor of same exact type which has flywheels removed and see how much longer it runs.    Decoders with increased capacitance/keep alive in part do what flywheels do--store energy.  One does it mechanically, the other electronically.  

BEMF is based on PID algorithems  and so depending on how you set them(each component of BEMF) up they can try to counter or enhance the flywheel.   Early BEMF algorithems were not very good particularly when consisting locos.

Richard

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Posted by riogrande5761 on Saturday, November 15, 2014 8:51 AM

jjdamnit

Hello All,

With the advent of programmable DCC acceleration and deceleration curves are flywheels on drivetrains relevant?

Thoughts?

Acceleration and deceleration curves aren't related to the flywheel principle much.

Now one thing DCC offers via some decoders is the Back EMF, which can help smooth out motor response in engines which are stiff - like some Athearn RTR engines.  Joe Fugate of Coos Bay fame has extolled this.

Basically some HO motors are a bit rough so flywheels were one way to help smooth them out because "mass in motion tends to stay in motion" (a principle of physics).  BEMF has been explained to help in a similar way.  

Rio Grande.  The Action Road

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Posted by Texas Zepher on Friday, November 14, 2014 9:43 PM

There is always the theory and the practice. 

In theory a keep alive capacitor should be much better than fly wheels, because of serveral reasons including the reverse power jitter that a DCC decoder can deliver to the motor when it looses power.

In theory you don't want fly wheels turning the motor into a generator and feeding electricity backwards into the decoder.

In practice the fly wheels smooth out the turning of the motor reguardless of the power supplied.

In practice I can not attribute a single decoder failure to power coming in backwards.

There are other practical matters unrelated to DCC that others have already pointed out.  A fly wheel adds additional weight to a loco where a same sized capactor would not weigh nearly as much.

For a science project I will someday actually take fly wheels out of a unit and do a head to head comparison.  Then I can get some real detailed information and respond in a much more intelligent manner.

 

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Posted by richg1998 on Thursday, November 13, 2014 2:29 PM

My steamers have a flywheel and do run nice under DCC but the slightest interruption from dirty track and the decoder resets, motion and sound. Flywheels may help over a dirty spot but the interruption occurs without Stay alive. I have experienced this a few times.

 

Rich

 

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Posted by mlehman on Thursday, November 13, 2014 2:24 PM

My understanding is that BEMF is becoming more sophisticated and recent decoders have lagely eliminated the issues encountered in consists, down hills and with flywheels. You may still encounter it with cheaper/older decoders. I wouldn't remove a flywheel just to fix a BEMF issue, I'd upgrade the decoder. Plus, with some flywheel installs, getting one off clean without damaging the motor can be an issue.

It was mentioned that flywheels add mass and you may sacrifice that in removing them. Sometimes it's space needed for a sound install and can't be helped, but your tractive effort will be reduced. But even non-flywheel mass helps a locomotive along simply by means of the inertia of its mass, so if you can work it back in elsewhere without throwing the balance of the loco out of whack (usually only an issue with steam), you'll not miss it too much as rotating mass.

Mike Lehman

Urbana, IL

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Posted by CSX Robert on Thursday, November 13, 2014 2:20 PM

jjdamnit

Hello All,

With the advent of programmable DCC acceleration and deceleration curves are flywheels on drivetrains relevant?

Thoughts?

 

Flywheels and programmable acceleration/deceleration curves serve two completely different functions.  The flywheel's purpose is to smooth out the drive train motion, including preventing stalls due to poor electrical pickup or dirty track.  Programmable acceleration/deceleration does not help in that regard.  The purpose of the programmable acceleration/deceleration is to simulate the mass and resulting momentum of a real locomotive.  While flywheels will add some momentum to a model locomotive, they will not add enough to even come close to simulating a real one.

 

In short, no programmable acceleration/deceleration curves do not render flywheels irrelevent because they serve different purposes.

 

What more closely serve the same purpose as flywheels are keep alive circuits and BEMF compensation.  Some may say that these have rendered flywheels irrelevant, but I still believe my locos run smoother with flywheels.

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Posted by Lake on Thursday, November 13, 2014 1:09 PM

rrinker

 I dunno, I've never removed the flywheels from any of my locos, and they all use BEMF decoders, and they most definitely do not run erractically. On the contrary, nice and slow tie to tie creep low speed and smooth acceleration alone or with a train behind. Also consisted together with BEMF still on.

                          --Randy

 

I also do as Randy, and have the same great results also. I have found the engines do work better with the BEMF still on.

Ken G Price   My N-Scale Layout

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Posted by Lake on Thursday, November 13, 2014 1:06 PM

Graffen
Well, results may vary.... I had problems with some loksound decoders with bemf when going up and down inclines. They would "hunt" and run uneven until I removed the flywheel. This was a Swedish locomotive with a BIG flywheel.

So you are saying that Swede's have bigger flywheels then Americans?Confused

Ken G Price   My N-Scale Layout

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Posted by Graffen on Thursday, November 13, 2014 6:57 AM
Well, results may vary.... I had problems with some loksound decoders with bemf when going up and down inclines. They would "hunt" and run uneven until I removed the flywheel. This was a Swedish locomotive with a BIG flywheel.

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Posted by rrinker on Thursday, November 13, 2014 6:03 AM

 I dunno, I've never removed the flywheels from any of my locos, and they all use BEMF decoders, and they most definitely do not run erractically. On the contrary, nice and slow tie to tie creep low speed and smooth acceleration alone or with a train behind. Also consisted together with BEMF still on.

                          --Randy

 


Modeling the Reading Railroad in the 1950's

 

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

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Posted by hobo9941 on Wednesday, November 12, 2014 11:25 PM

That mechanical advantage is absolutely used by DCC. You still get the motor spinning over dead spots.

I dunno. I'm still amazed how quick a heavy six axle loco with flywheels suddenly stops on a dead or dirty track. Whistling

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Posted by Graffen on Wednesday, November 12, 2014 10:54 PM

Flywheels, regardless of how they help reduce bad running drive trains, are not really compatible with DCC.

At least if you intend to use BEMF. A flywheel will always work against it, making the running characteristics erratic and unpredictable. Check with the decoder manufacturers, they will most likely tell you the same.

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Posted by richg1998 on Wednesday, November 12, 2014 11:50 AM

With any power interruption, the microprocessor in the decoder is going to reset, flywheel or no flywheel.

Rich

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Posted by Train Modeler on Wednesday, November 12, 2014 8:15 AM

The flywheel maintains torque when the motor runs and even when power is cut off.   It helps, how much depends on many things including clean track, locomotive mechanism stiffness, etc.   They also help with added weight and so you get two positive effects. 

Richard

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Posted by tomikawaTT on Wednesday, November 12, 2014 2:05 AM

Flywheels were originally added to smooth out the mechanical side of operation by eliminating jackrabbit starts and stonewall stops - a common result of controlling motor speed with a 40 ohm rheostat not wired as a potentiometer.  One early experiment geared the flywheel UP from the motor RPM, which led to interesting gyroscopic effects.

With the old amp-hog motors and the capacitor technology of the day, the capacitor that could equal the energy storage of a flywheel would have been as big as the loco's boiler.  With present-day motors and capacitors, the situation has changed drastically.

However, if there are no interruptions in rail power to the loco pickups, neither flywheels nor capacitors are necessary.  With my electrically bulletproof trackwork, I get along without having either.

Chuck (Modeling Central Japan in September, 1964)

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Posted by Mark R. on Tuesday, November 11, 2014 9:56 PM

I frequently remove one flywheel in order to fit a larger speaker / enclosure in engines - especially switchers.

You can even eliminate both flywheels and add a Keep Alive module as it pretty much negates the need for flywheels. They are a dream come true for older brass that doesn't have flywheels !

Mark.

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Posted by gmpullman on Tuesday, November 11, 2014 9:43 PM

Seems to me...

Flywheels became all the rage in the early '80s and I recall many of the Athearn locomotives of the time having them as standard equipment.


I remember some of the motors of the era were still three pole, then they developed five pole, then skewed armatures. All of this was to reduce the "cogging" effect as the armature rotated between the poles.

Pulse power came along to introduce a vibration (small doses of AC?) to also overcome this cogging effect and to help the armature overcome the resistance of bearings, sticky grease and loose fitting drive components.

In my untrained and unscientific opinion I think the flywheels are still a very important part of the total drive-line component. Sure, you can electronically control the decay or the increase of the voltage and frequency to the motor but I believe having a mechanical device (the flywheels) to help smooth the rotation of the drive shaft definitely helps smooth out the "bumps."

I'll never forget the time I had four Life-Like E-8s running flat out (pre DCC) and I tried to make an emergency stop. I'll bet it took six feet to get that train to finally halt. I don't remember what the result was... I probably rear-ended a standing train but the inertia provided by those large flywheels sure kept the motor shaft turning!

In the DC days the flywheel helped overcome some current pick-up irregularities but with DCC a break in the current causes more headaches, especially with sound, since everything has to come back to life after a power interruption. Here is where keep alive capacitors earn their keep. With the flywheels at least everything keeps moving and you minimize the time that the power is actually interrupted.

I'm sure others will contribute with more detailed info but this is just my take on the subject... Ed

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Flywheels & DCC?
Posted by jjdamnit on Tuesday, November 11, 2014 8:54 PM

Hello All,

With the advent of programmable DCC acceleration and deceleration curves are flywheels on drivetrains relevant?

Thoughts?

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

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