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Author Topic: Train wont slow when going down hill  (Read 6656 times)
Mark FL


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« on: June 13, 2013, 11:35:37 AM »

I am a little new to the DCC world and wonder if someone can tell me why my train speeds up when going down hill? I have tried to set the CV code but then the train will lurch going down hill. I have a 2% slope and have been pulling 5 coal cars.  Does anyone have any thoughts?
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jbrock27

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« Reply #1 on: June 13, 2013, 11:55:34 AM »

I know very little about DCC Mark, but this is known as "cogging".  Does this loco have flywheels?
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Mark FL


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« Reply #2 on: June 13, 2013, 11:59:03 AM »

Great Question J. My gut feeling is No. (But I will look).
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jbrock27

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« Reply #3 on: June 13, 2013, 12:07:39 PM »

Cool Mark.
If you GOOGLE "cogging HO locos"  you should find lots of posts about it.  It could provide you with an answer faster than here. 
People love pictures, so maybe if you posted some here, lots of folks would likely look at it with you.
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Mark FL


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« Reply #4 on: June 13, 2013, 12:19:26 PM »

I will check that out. Great help Thanks !!!
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jbrock27

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« Reply #5 on: June 13, 2013, 01:02:33 PM »

You are welcome Mark!  I hope I was able to.
Like I said, I don't know ins and outs of DCC but from the mechanical side of what I have read in the past about "cogging" it has to do with too much "play" with regard to the worm gears and how they interact with the gears that drive the locos drive wheels.  Shows up going "downhill" bc of the momentum created by the loco going downhill and not everything in the mechanism is meshing/rotating in sync.
Be sure to check back here as you will probably find additional input(s).
Good luck with it.
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richg
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« Reply #6 on: June 13, 2013, 03:53:00 PM »

Cogging is the armature resistance to turning because of the interaction between the magnets and motor coils.

http://en.wikipedia.org/wiki/Cogging_torque

No idea about your issue though. Usually I reset the decoder to original specs when something weird happens.

Rich
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richg
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« Reply #7 on: June 13, 2013, 04:19:06 PM »

I have read of some locos with to much end play in the motor armature causing this issue. Generally you have to fake the shell off the loco and observe the motor armature movement. Might be difficult with steamers but usually not diesels.
More info about which loco might help here. We have no idea on which scale you are talking about.
There are forums here for different scales.

Is it possible to put the DC adapter in place of the decoder and try it on DC?

Rich
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jbrock27

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« Reply #8 on: June 13, 2013, 04:31:45 PM »

From this very Forum Re: "Cogging"

sd24b

     Re: Max slopes for new HO engines?
Reply #1 on: September 21, 2012, 11:00:27 AM    

--------------------------------------------------------------------------------

4% is pretty steep.  However, 2 or 3 diesels should be able to handle your train lengths.  Not sure on your steam.   6 axle diesels generally pull better than 4.  What I have found to be a small problem is not working trains upgrade but going down grade.  Some engines suffer from cogging.  the weight of the train pushes against the engine forcing the worm gear forward.  Shouldn't affect you unless you're running longer trains.     Phil

You were part of that discussion Rich:

richg

    Re: Max slopes for new HO engines?
Reply #13 on: September 24, 2012, 05:44:44 PM    

--------------------------------------------------------------------------------

Take a look at the below link. Layouts for different scales but some may offer an idea. You can scale some up or down to the scale you want.

http://www.thortrains.net/

Rich
 
 
 
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JerryB

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« Reply #9 on: June 13, 2013, 05:46:37 PM »

From this very Forum Re: "Cogging"
sd24b
     Re: Max slopes for new HO engines?
Reply #1 on: September 21, 2012, 11:00:27 AM    
--------------------------------------------------------------------------------
4% is pretty steep.  However, 2 or 3 diesels should be able to handle your train lengths.  Not sure on your steam.   6 axle diesels generally pull better than 4.  What I have found to be a small problem is not working trains upgrade but going down grade.  Some engines suffer from cogging.  the weight of the train pushes against the engine forcing the worm gear forward.  Shouldn't affect you unless you're running longer trains.     Phil

You were part of that discussion Rich:

richg

    Re: Max slopes for new HO engines?
Reply #13 on: September 24, 2012, 05:44:44 PM    

--------------------------------------------------------------------------------

Take a look at the below link. Layouts for different scales but some may offer an idea. You can scale some up or down to the scale you want.

http://www.thortrains.net/

Rich

Forum replies or not, the OP's described problem is definitely NOT termed "cogging." As richg wrote, "Cogging is the armature resistance to turning because of the interaction between the magnets and motor coils."

The OP's described problem is normally termed 'surging' and is usually caused by the interaction of a worm & worm gear. It shows up on steep down hill sections because the force of the train pushes against the locomotive and drive mechanism such that the motor is acting as a brake. The slack between the worm gear and the worm runs in and out, causing a surging action.

There is really no simple solution, but things to check are the mesh between the worm and worm gear. Making them mesh closer will lessen the possibility of surging by eliminating the 'space' that is allowing the surges. You can check this by turning the wheels by hand while watching the motor shaft. Another thing to look for is the amount of end play in the motor shaft. That can also cause surging. Putting washers on the motor shaft to minimize the end play is usually possible.

Putting retainers to add drag to the train in the form of springs on wheel sets can also help, but that adds drag when going uphill.

Lessening the grade is probably the best solution, but not always possible.

Happy RRing,

Jerry
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Sequoia Pacific RR in 1:20 / 70.6mm
Boonville Light & Power Co. in 1:20 / 45mm
Navarro Engineering & Construction Co. in 1:20 / 32mm
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Jerrys HO
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« Reply #10 on: June 13, 2013, 06:03:35 PM »

I have 3% grades (give or take a few) on my layout and had my loco's speed up and jerk on the down side. Recently I purchased a couple of Digitrax DZ125PS decoders and have installed them in my SD40-2's and SD45's and they eliminated those problems and more.
It maintains the speed going up also, as the decoders have Back EMF. What a difference it makes. Here's a link where I got them.

http://www.ebay.com/itm/Digitrax-DZ125PS-DZ-125-PS-Decoder-New-Z-Scale-Bob-The-Train-Guy/380583519701?_trksid=p5197.m1992&_trkparms=aid%3D111000%26algo%3DREC.CURRENT%26ao%3D1%26asc%3D14%26meid%3D8357648008767729868%26pid%3D100015%26prg%3D1006%26rk%3D1%26sd%3D380583519701%26

Jerry
« Last Edit: June 13, 2013, 07:01:55 PM by Jerrys HO » Logged
Jerrys HO
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« Reply #11 on: June 13, 2013, 07:54:21 PM »

Anyway...
Mark it may be the same problem I was having on my steep grades. With the basic Bachmann decoder which is what all my loco's have I will be replacing them with the Digitraxx decoder and Jeff W. had once told me about the NCE board type decoder was also good. I may use them for my geep's just need to get that PN# again.
Upgrading to the Back EMF is the first thing I would try.

Projects are moving very sloooow. Wink

Jerry
« Last Edit: June 13, 2013, 07:56:22 PM by Jerrys HO » Logged
JerryB

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« Reply #12 on: June 13, 2013, 08:44:23 PM »

So JerryB except for our different use of the terms "cogging" and "surging", looks to me you are describing the problem the same way I did.    How magical.

"Cogging" is the common description of a motor's performance. It is usually noticed in two pole (DC) motors with a three segment armature. When operating at very low speeds, cogging is noticed by an engine making small 'jerks' along LEVEL track. It does not induce what is commonly called surging.

"Surging" is the common name for the problem of slack running in and out when a train is going downgrade. RichG and others already covered this above.

Cogging and surging are no more the same than fire and water, but I am certain (from the tone of your follow up posts) that you are not interested in this. Fine with me, but you might consider that calling fire water might get someone hurt, just like calling surging cogging might mislead someone looking for a solution.

In fact, the real solution might be in the decoder or its settings. Hard to tell long distance.

Happy RRing,

Jerry
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Sequoia Pacific RR in 1:20 / 70.6mm
Boonville Light & Power Co. in 1:20 / 45mm
Navarro Engineering & Construction Co. in 1:20 / 32mm
NMRA Life Member #3370
Member: Bay Area Electric Railway Association
Member: Society for the Preservation of Carter Railroad Resources
jward


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« Reply #13 on: June 13, 2013, 09:26:11 PM »

I am not sure what the problem is, but locomotives shouldn't surge going down a 2% grade with 5 cars. that said, I have noticed in Bachmann dcc locomotives without flywheels a tendency for the locomotive's motor to stop and restart, causing the locomotive's wheels to slide. resetting cv3 to 3 seems to cure that problem. cv3 is the acceleration side of the momentum control, cv4 is the deceleration side, you may want to set that to 3 as well. this is a simple programming fix that, if it works for you will save you from the cost of replacing the decoder.
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Jeffery S Ward Sr
Pittsburgh, PA
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