Is NCE Momentum description confused? No, I was. Thanks

[gregc]

I'm a bit confused by the NCE Power Cab description of momentum, cv3 and 4,  in their manual (p. 34) which indicates a time in "seconds to full speed" for each rate setting in the cv3.   Their manual references NMRA RP 9.2.2 which under the description for cv3  describes its value as an acceleration rate and specifies an equation for the rate in sec/step.   Isn't the NCE description wrong?

in other words, my interpretation of of the NCE description is that for the same cv value, it would take the same amount of time to reach the selected speed regardless if the speed is fast or slow.   The NMRA description make sense, that it would take longer to to reach a higher speed than a slower speed.

In addition, the NCE, manual describes setting the deceleration rate in cv4 to 1/2 the acceleration value in cv3.   But while the acceleration rate, cv3, should depend on the weight of the train or the number of cars, shouldn't the deceleration rate, cv4, depend on the braking level and NOT the number of cars?

in other words, you can set the deceleration rate in cv4 and leave it alone, but the acceleration depends on the number of cars.

another thought about the NCE throttle is shouldn't it have a brake button that is active when using momentum?    When the throttle is closed, the train momentum should maintain or slowly lose speed.   A brake button would cause the train to lose speed more quickly.    (didn't the tat-iv have 3-4 brake settings)?

[CSX Robert]

gregc

...in other words, my interpretation of of the NCE description is that for the same cv value, it would take the same amount of time to reach the selected speed regardless if the speed is fast or slow...

Where the manual says "seconds to full speed", it is referring to full throttle speed, not the selected speed. 

[tstage]

Greg,

If you want to quickly see momentum in action, just use the momentum button on your Power Cab.  It will give you a choice between 0 and 9; 0 being no momentum and 9 being the longest.  (I think at the 9 setting it would take over one minute to get from 0 to top speed.)

IIRC, the momentum buttons automatically use the 1/2 rate for the deceleration.  CVs 3 & 4 will allow you to adjust both acceleration and deceleration to your liking.

Tom

[rrinker]

 The momentum in DCC is in the decoder, not the throttle. All the NCE momentum button is doing is ops mode programming CV3 and CV4. Therefore, a brake button would do nothing unless a specific decoder supported it.

 Some do - F6 is used for the default brake, which is a diesel decoder may also activate the dynamic brake, and slow the loco faster than the momentum setting is slowing it. Releasing the brake (F6 off) allows it to speed up, or reduces the rate of slowing back to the momentum setting. Don't know of any motor only decoders that have a brake, just sound ones.

 

              --Randy

 

[gregc]

with cv3 and 4 set to zero, couldn't the throttle implement momentum and braking?

[tstage]

Greg,

At zero there would be no momentum at all and the locomotive would speed up and slow down instantaneously - i.e at whatever rate you moved the thumbwheel and/or pressed the speed buttons.

Tom

[gregc]

tstage

At zero there would be no momentum at all and the locomotive would speed up and slow down instantaneously - i.e at whatever rate you moved the thumbwheel and/or pressed the speed buttons.

i realize that there may not be a throttle that works the way i describe

the throttle sends speed commands to the decoder.   I doesn't have to send the speed selected by the thumb-wheel.  The throttle could slowly  increase the speed setting based on a momentum setting in the throttle until the thumb-wheel setting is reached.

The throttle could then be closed, that is, the thumb wheel set to zero to allow the train to coast.  The throttle continues to send the speed command corresponding to the current speed of the train and accounting for a slow decrease in train speed due to drag.

A brake button on the throttle would cause the throttle to more quickly reduce the speed command beign sent.  Different brake buttons could cause different rates of descrease.

maybe this is where the hobby is headed -- the home made dcc tat-iv using a pic processor

[fwright]

gregc

i realize that there may not be a throttle that works the way i describe

the throttle sends speed commands to the decoder.   I doesn't have to send the speed selected by the thumb-wheel.  The throttle could slowly  increase the speed setting based on a momentum setting in the throttle until the thumb-wheel setting is reached.

The throttle could then be closed, that is, the thumb wheel set to zero to allow the train to coast.  The throttle continues to send the speed command corresponding to the current speed of the train and accounting for a slow decrease in train speed due to drag.

A brake button on the throttle would cause the throttle to more quickly reduce the speed command beign sent.  Different brake buttons could cause different rates of descrease.

maybe this is where the hobby is headed -- the home made dcc tat-iv using a pic processor

 

I very much doubt the hobby will return to hand throttle-based momentum and braking.  The last iterations of TAT and similar DC throttles tried to establish custom settings (typically accel/decel rates, min/max voltages) for each locomotive.  One throttle used a separate EPROM for each locomotive to achieve this.  All of this has been moved into CV land in the DCC decoder world, where it is automatically customized for each locomotive.

 

Your envisioned operation is easily acheived on an individual locomotive basis by customizing the appropriate CVs in a given decoder.  Steven Hatch has set up Tsunami decoders to conduct operations simply by blipping a brake and throttle button (or could be forward and reverse buttons).  This is very similar to a two button or spring toggle DC transistor throttle (SWAT might have been the throttle name?) I remember reading about in RMC.

 

Putting adjustable configuration of speeds and accel/decel in both the DCC throttle and DCC decoder would be a nightmate logisticallly and operationally.  Much better to keep the configuration variables in the decoder where they are set and adjusted for the individual locomotive, rather than treating all locomotives the same.

 

my thoughts, your choices

Fred W

[rrinker]

 I'm having deja vu all over again.... I think we had this discussion before.

ANd I'll say the same thing - with a Digitraz Zephyr and the jump ports, you could hook a TAT IV (with the pulse turned off - not needed and doesn;t work in this instance) to one of the jump ports and get this very effect - the throttle doing all the braking and momentum and set the decoder to 0 momentum.

And I agree with Fred, the functionality belongs in the decoder, so that the loco response can be consistent no matter where you run it.

               --Randy

 

[gregc]

rrinker

And I agree with Fred, the functionality belongs in the decoder, so that the loco response can be consistent no matter where you run it.

i don't understand why momentum should be in the loco.  Isn't momentum/acceleration, dependent on the length of the train and should be easily changeable as cars are added or removed?

[rrinker]

 The thing is, with 128 speed steps and encoder throttles, you can easily simulate as much or as little momentum as you want.Using the right sound decoders, you cn even get the proper sounds, either a lithly loaded loco takin goff or one trying to start a heavy train, all just by changing how fast you crank up the throttle. In fact, it can work very much like a real loco - rapidly opening the throttle then closing it down to prevent slip (ok the slip part is imaginary in our models..). All just by putting some momentum on the loco.

 I think that's the purpose of the momentum button on the NCE throttles - so you cna eaily change it as you change the train size, instead of rememebring CV3 and CV4, you just hit the momentum button.

                --Randy

 

[selector]

gregc

...  Isn't momentum/acceleration, dependent on the length of the train and should be easily changeable as cars are added or removed?

  Yes, in the real world, that's partly how it works.  The rest is up to the loco's engineered capacity and the hogger's intentions for apportionment of that capacity.  A low-drivered brute with four cylinders, a booster, and a large hot boiler with over 260 psi will accelerate a smallish coal drag more quickly than it would a large one, but not as quickly as a high-drivered Pacific with four commuter coaches behind it.  But the impetus in all cases is resident in the locomotive, and that's what the decoder mimicks for you.

If you want a jackrabbit start with your Pacific, you set your CV 3 with a mid-range number.  If you want your long coal drag headed by a lone Y6b, I would (and do) set its CV3 with something near 80-90% of the maximum value for that CV.  Whenever I decide the train is substantially lighter, I always have the option of entering programming on the main, selecting CV3, entering a half-value or some other I choose, pressing enter, and I have my loco doing what I think it should for the trailing tonnage.  It takes as long to do it as to read it.

Crandell

 

[maxman]

gregc

Isn't momentum/acceleration, dependent on the length of the train and should be easily changeable as cars are added or removed?

If we are really going to be concerned about this, then the length of the train is not one of the determining factors.  It is the mass of the train that is important.  A train of 25 loaded 100 ton hoppers will probably have the same momentum as 50 or more empties.

[hon30critter]

Crandell and Gregc:

With the momentum control on the Power Cab you don't even need to read the CVs.

Dave

[selector]

Ah, Dave, that's a new feature for me.  Does the momentum apply to all locos acquired on the throttle, or just to a given decoder at the time it was adjusted?  In any case, simply dialing up or down the momentum seems to be a quick fix depending on trailing tonnage.

Crandell

[tstage]

As far as I understand, Crandell, it only affects the individual decoder.

Tom

[rrinker]

 Just the selected loco - it does Ops Mode to set CV3 (and I think it sets CV4 to half that, by default). It's just a shortcut for Ops Mode programming just those specific CVs for momentum.

             --Randy

 

[tstage]

rrinker

(and I think it sets CV4 to half that, by default)...

That is correct, Randy.

Tom

[hon30critter]

selector

Ah, Dave, that's a new feature for me.  Does the momentum apply to all locos acquired on the throttle, or just to a given decoder at the time it was adjusted?  In any case, simply dialing up or down the momentum seems to be a quick fix depending on trailing tonnage.

Crandell

Tom and Randy have explained how it functions. Basically the cab has a 'momentum' button which offers a scale of 0 - 9. '0' is obviously no momentum and '9' let's the locomotive carry on for several seconds in the lower speed ranges and , I believe, up to a minute from top speed. It also affects start up so you can quickly go from a heavy load to a light load after dropping off a train by pushing two buttons.

Dave