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NCE Cabs - Momentum button - Avoid using

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Some years ago when I first got an NCE system I noticed what I thought at the time was a very useful 'momentum' button on the cab, but it is a disaster because it causes CV3 (accelaration) and CV4 (deceleration) on loco decoders to be overwritten each time it is used which really messes up sound decoder locos, and even non-sound locos where CV3 and CV4 had been carefully set to give optimal prototypical running performance. I recommend taping over this useless button. If Momentum button is used inadvertently reseting the decoder on the programme track should put everything back to normal (eg. CV8=8 for most decoder manufacturers).  I investigated gluing the momentum button on my cabs to prevent accidental use but decided against so as not to compromise NCE warranty. Otherwise the NCE DCC system has proven very useable, especially so for sound locos and consisting double headers of baby GMs. I've reconfigured the 'option' button on my cabs to operate like a shift button for DCC sound functions (eg option+7 for FN17, option+option+4 for FN24), which gives quicker access to all 28 functions on sound decoders. If there was one single software change I would like to see its that any throttle input should escape and cancel any level of menu the cab may be in (eg: pressing 'expn' to view active functions should auto exit if a throttle input is made rather than having to press escape or expn again).


PS: Remember a decoder reset also defaults a locos address back to the default of 3, so the loco address may have to be reassigned after any decoder reset.

Edited by Noel
missing info
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7 minutes ago, richrua said:

Hi Noel, I know I could just dig out the manual to find out, but what is the actual function of the Momentum button? I've always thought it has been placed in a very prominent position on the controller. 

It was to enable the loco cab driver to alter the inertia (ie momentum) of a locomotive (ie increase the accelaration and braking distances). Years ago in the DC world we were all chasing DC controller that had 'inertia' simulation and a break knob. These just simulated acceleration and braking by electronically delaying the voltage increase as the regulator knob was turned up, and delayed the voltage drop using simulating braking. 

This was based on an electronics kit I made up in the 1970s when 'inertia' was all the rage, but is now a routine part of DCC systems (primarily but not exclusively via CV3 and CV4).


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1 hour ago, richrua said:

Ah ok , thanks Noel. I notice my locos take an extra little bit of time to stop as opposed to a DC dead stop, I wonder have I inadvertently turned on momentum

Or more likely the default values in your decoders were pre-set for CV3 and CV4 (acceleration/decelaration). Personally I prefer to use the default values for CV3/4 in sound decoders, and manually adjust the values for non-sound decoders to get trains to drive as prototypically as suits my personal driving style. If the momentum button was accidentally used resetting the decoder or reinstating CV3 & CV4 values should restore matters.

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8 minutes ago, mmie353 said:

Hmmm... interesting to know, I was actually starting to think of looking at getting a new DCC system in 2021 at some point. I was actually looking at NCE at my local model railway store yesterday as they had them and Digitrax. 

I've only used Lenz, NCE and Roco, and for an afternoon got to play with a prodigy advance and an eCos. Its a purely personal thing but I did like the ergonomics of the NCE cabs which facilitated eyes off one handed operation and suited my penchant for operating sound locos. I disliked using touch screen cabs due to the lack of tactile feedback with throttle inputs which required eyes on the cab screen using a touchscreen slider icon to control throttle. When I started out on DCC my mindset was still in DC mode and I really wanted cabs with either throttle sliders or rotary knobs (ie like DC had), instead of throttle buttons +/-, the NCE had both a rotary knob and Throttle +/- buttons as well as +4/-4 buttons which left both options open, but I quickly changed mindset and find I never use the throttle knob, just the INC and DEC buttons which is handy for blind eyes off one handed use leaving me free to watch the loco and operate points while shunting. All the different systems has their own pros and cons and will suit different personal tastes and driving styles. The Roco Z21 appealed as it allowed the use of smartphones as inexpensive wireless cabs, but with eye on touch screen throttle control. One advantage of smartphone cabs is the customisation of function button labels to match the sounds available on a particular loco. The Lenz cabs are compact and were once the gold standard, personally I just preferred the feel in hand of the NCE dog bone snapped cabs and the size and tactile feel of the buttons and controls. Great menu interface makes them really easy to setup and programme. The underlying base electronics behind DCC pre-dates Zero1 and is very much late 1970s technology, but modern decoders have powerful functionality if a rather primitive and slow comms protocol. IMHO concepts such as CVs should be invisible to users in this day and age and buried under a simple human interface. Tooling up on DCC is fun and stimulating though.

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From what I remember the Momentum button allows you to enter a value of 0-9.

Entering a value of 0 turns off acceleration and deceleration. When a value of 1-9 is entered the Powercab takes that number, multiplies it by a factor of 8 and writes that value to CV3, then writes half that value to CV4. So any values you already have programmed to a loco will be overwritten,

Problems can arise because some sound decoders such as Zimo have specific values in CV3 and CV4 that are neceasary for realistic operation of the sound file. 

Loksound decoders have a different problem; acceleration and deceleration values differ from NMRA recommended practices so that their values need to be higher to match other brands of decoders. 


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