my limited experience is that it is more up to the engine. i have run both though it's been a while since the DC days. i have a kato that is cluncky at very slow speeds and an atlas that is very smooth. i would say the DCC can do what you ask. not sure about exceeding DC.
jbauerA quick question for those who have operated both DC and DCC. I am constructing a small (18"x 12') shelf switching layout. Typical operating speeds will not exceed 10 scale mph and for the most part will be much less. Loco is a P2K GP-30 (with non-cracked axle gears!) My priority is smooth, well controlled slow speed operation. Do current decoders offer superior motor control compared to a quality DC throttle at these speeds, or do they just match a quality DC throttle? I don't want to start another DC/DCC battle. I am aware of the other numerous benefits of DCC. Just need info. concerning slow speed motor control. Thanks for your help!
I use DC, I use the wireless radio throttles made by Aristo Craft called the Train Engineer. The Train Engineer uses a square wave pulse full votage output to control the motors, very similar to a DCC decoder. It provides performance equal to DCC in my testing and use of it. I have a good basis to compare since I operate on four other layouts that are DCC.
Most of my Diesel fleet is Proto2000 and they run great on my Train Engineer throttles, slow speed is fantastic.
There are also other DC throttles on the market with this type of output that provide speed control equal to DCC.
Such throttles also provide good constant lighting effects because the lighting circuits see the voltage, not the high frequency pulse, and light at full brightness as soon as voltage is on the track.
If you are only operating one loco at a time, the Train Engineer would be a simple and low cost throttle that would give you wireless control and good performance. I know one modeler who has a large (his whole basement, about 1200 sq ft) switching layout, he uses one Aristo Train Engineer and loves it.
Let me know if you want more info, I can give you some specific tips on using the TE for HO.
Sheldon
The nice thing, IMO, with DCC is that decoders can be speed curved, drastically improving the performance of most locomotives. If you have a locomotive that takes quite of bit of voltage to move, that can be programmed into the decoder. It a kick start voltage used to get the motor going. I have two sets of curves that I use for my engines, Switcher and road engine. Generally my switchers are set up for finer control than the road units. I max their speed out at 30 mph. This allows me to have much finer control at lower speeds. For example, I use a UT4 to control my yard switcher (an Athearn BB SW1000, stock motor). This engine, with a little tweaking and some lubrication, is a pretty decent little runner. With some programming (raising the kick start voltage, and adding my switcher speed curve) I was able to get this locomotive to run as well or better the my new Athearn RTR SW1000 (the one with the newly designed driveline and mashima motor). Most of my fleet of locomotives are super detailed Athearns. I do have several proto 2000, kato and Atlas locomotives as well. The speed curving allows me to run all these locomotives together.
Quality decoders like NCE, TCS, Digitrax, and Soundtraxx, are all capable to speed curve, drastically improving fine motor control.
Colorado Front Range Railroad: http://www.coloradofrontrangerr.com/
jbauerA quick question for those who have operated both DC and DCC.....Typical operating speeds will not exceed 10 scale mph and for the most part will be much less. Loco is a P2K GP-30 (with non-cracked axle gears!) My priority is smooth, well controlled slow speed operation. Do current decoders offer superior motor control compared to a quality DC throttle at these speeds, or do they just match a quality DC throttle?....Just need info. concerning slow speed motor control. Thanks for your help!
Are you aware of how slow 5 smph is? At 5 scale mph, regardless of scale, a 40ft box car takes 6 seconds to go by a point. That's 6 seconds for 1 car to go by a switch stand, and over 45 seconds to pull a 5 car string from a track, with the clock starting when the throttle is cracked. Pulling and breaking the 5 car cut into 2 blocks in a yard is over 3 minutes of real time if operating at real scale speeds - close to what the prototype takes. Many model railroaders die from boredom operating at those speeds. Perhaps you don't or won't.
Most HO locomotives are geared to operate at minimum motor RPM at 1-3 scale MPH so that they can have a 60 scale MPH or faster top speed. Another point is that our motors take more voltage (and current) to start turning than they do to continue turning. With a motor running at very close to its minimum RPM, and any stall requiring extra power to start moving again, it's easy to see why stalls are common at switching speeds. Any spot of dirt on the rails that interrupts the power flow stops the engine. Besides dirt, track irregularities that temporarily cause a wheel to lift (such as filled in frogs) can also cause stalls. Bottom line is that all wheel pickup needs to be working on all wheels for good slow speed operation. Powered frogs on turnouts also contribute to preventing stalls.
Sharp, narrow pulses of nearly full voltage "kick" the motor. The momentum of the flywheels and motor keep it going until the next pulse comes to provide a new "kick". This is how ultimate slow speed is achieved. But our motors run much cooler on pure, filtered DC. The motors also "growl" when the pulse repetition rate (frequency) is low enough for our ears to easily hear the first few harmonics of the frequency. Finally, if the motor and flywheel do not have enough momentum between pulses, the locomotive can appear to operate in a series of jerks.
DCC "silent drive" decoders use a pulse frequency with harmonics out of the audio range. This eliminates the growling and substantially reduces the heating problem. The price paid for the higher pulse frequency is the loss of the very slowest tie-to-tie creeping ability. Because pulse width modulation (PWM) is a very efficient method of generating pulses, it is the standard method for controlling DC motors with a DCC decoder. Any other method produces too much heat in the decoder and/or increases space needed for the decoder. The better DCC decoders allow tuning of key variables (pulse frequency, pulse voltage, minimum and max pulse width) to a locomotive through various CVs.
DC throttles don't have the limitation on heat generation and space that DCC decoders do. Consequently, there are a much wider variety of pulse generation and motor control schemes used in DC throttles. Different pulse and motor control schemes are adopted and used to achieve a variety of purposes and priorities, including low cost, more universal compatibility across a wide range of locomotives, minimize heating, minimize or maximize operator adjustments, etc.
The Train Engineer (and some other) DC throttles mentioned by Sheldon use PWM, just like DCC decoders.
MRC Tech series power packs and the True Action Throttle (TAT series) typically use a more rounded pulse at a lower pulse repetition rate. In the better throttles (TAT and others), various parameters such as the pulse rate and pulse voltage are adjustable, and can be tuned to a particular locomotive. As the throttle is opened more, a pure DC component is introduced, and the pulses die out (no longer needed). This system gets away from the heating issues, and produces smoother running at anything above minimum speeds.
hope this helps
Fred W
fwright Another point is that our motors take more voltage (and current) to start turning than they do to continue turning. With a motor running at very close to its minimum RPM, and any stall requiring extra power to start moving again, it's easy to see why stalls are common at switching speeds.
Both BEMF and the speed curves can help. I'll not doubt that a good quality PWM DC throttle is CAPABLE of just as good a low speed operation (it's basically driving the motor the same way a DCC decoder does), but with the ability to set a speed curve in the DCC decoder you can have the full range of the throttle, 28 or 128 speed steps, be only 0-10 or 15 smph of the loco. That means the difference for each tiny tweak of the speed knob is so small that you won't even see it. This is probably, however, overkill. Another thing you cna do it set up the speed curve so that your 0-10smph is covere by all but the last couple of speed steps, allowing full 'ludicrous speed' on the top speed step so you can move the loco around quickly when you need to but most of the time it will oeprate within your desired slow speed band.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
CSX Robert The big advantage to DCC in this situation is being able to tune each decoder's output to a specific engine
Some DC throttles are also tuneable (usually through analog means rather than CVs) to each locomotive. But when you switch locomotives being controlled with the throttle, you must change the tuning. DCC shines with multiple locomotives and operators because of directly addressing the microprocessor (with stored CVs) in the locomotive instead of in the throttle. In times past, plugs have been made for DC throttles with the customizations for a given locomotive. You plugged in the appropriate plug for the locomotive, and then had a "tuned" throttle.
Frankly, the standardization of DCC processes and methods (like Decoder Pro software) makes DCC the easier system to tune to a specific locomotive.
But for most folks, a default setting that suits most locomotives (just as with DCC decoder defaults) is pretty effective. Only when the absolute maximum is needed out of a locomotive, or the locomotive control needs don't fit the defaults very well, will most people bother to tweak the default settings of the DC throttle or DCC decoder CVs.
I personally use a simple non-pulse DC test track to get the mechanism just as good as I can get it before even thinking about playing with CVs or DC throttle settings. I don't want throttle or decoder tuning to mask problems in the mechanism. I also insist on remotoring/regearing my locomotives for lower speeds at 12V (top speed of 30-45 for rod engines, 15-20 for geared), which leads to less need for sophisticated throttles/decoders for switching speeds. On my small layouts, such speeds are quite appropriate. However, some will find things too slow for them.
Bottom line: if your locomotive currently performs adequately at the speeds you want, either DC or DCC will work equally well. If you need to tweak settings to get the performance you want/need, for one locomotive either DC or DCC will work equally well. Once you get to tweaking more than one locomotive, DCC and Decoder Pro is a more readily available and standardized way of accomplishing the goal.
my thoughts, your choices
As you already know, and from the thoughtful responses posted so far, there are many variables associated with either system you're considering. But given the type of layout you are planning (as well as the subject of your post), I want to give you some data on one of my current set-ups as an example of what is possible -- though perhaps not always achieveable -- with DCC.
The power source for my 4'x8' layout is an NCC PowerCab. I have an Atlas B40-8W with just a few hours running time in which the factory decoder was replaced with an ESU LokPilot Basic ($19.50) that has back EMF. The installation was made by a professional installer and the gear train was cleaned and lubed at the same time. This is a very basic decoder with only a few, modifiable configuration variables. I have adjusted mine to achieve the best possible slow speed control
Using 128 speed steps, here are the speeds in scale miles/hour this setup exhibits the minute it's powered up (not requiring any previous "warm-up"):
Speed Step SMPH
1 0.42
2 0.68
3 1.36
18 10
126 61
Because of the BEMF, those low speeds are rock-solid smooth. This loco can approach a car to be coupled, slow prototypically, and (only if desired), couple using just the slack in the couplers (Kadee) without moving the car being coupled. Not everyone likes to operate in a "real time" atmosphere, but I do and this loco is a joy to run.
I have run DC for years. When I got into DCC it was still young and BEMF was only available in really expensive decoders. Now you can get a TCS decoder with BEMF for around $20. Another thing to help you do slow and steady is to swap out the P2K trucks with a set of Athearn trucks and find a set of Ernst super gears. This will knock down your top end but will let the motor spin faster at the slow pace you want to run. I put a set of super gears in an SD9 about twenty years ago and use the loco for mainly heavy switching. On DC it ran great. With an inexpensive decoder and BEMF it is the sweetest running loco in the fleet. Top end is about 30 SMPH. On speed step one you can barely see it move.
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
Not only do you have BEMF, but you also have several other settings on decent decoders. You can kick the motor with voltage spikes to make it creep. The adjustments are how hard you kick , how often you kick and how long each kick is. I've seen video's of loco's where you can barely see them move, but they are nice and smooth.
Springfield PA