A 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!
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.
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.
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.
Shar
These are two areas where Bemf compensation can really help. As he stated, it takes more voltage to start a motor than to keep it going, so for the absolute minimum speed you would have to turn the throtte up enough to get it moving and than back off slightly. Bemf compensation, if tuned correctly, will, at speed step 1, increase the decoder output until the motor starts turning and then actually back off the voltage and maintain enough to just keep the motor turning.
Also, when running at minimum speeds it takes very little additional resistance(mechanical, not electrical) to stall the engine - it could be as simple as a wheel hitting a mismatched rail joint. With Bemf compensation, if the engine encounters a mechanical resistance, the decoder will increase the output to overcome it and then, to maintain a consistent speed, it will decrease the output once it has cleard the resistance.
A DC throttle can do anything a DCC decoder can do, including having Bemf compensation. The big advantage to DCC in this situation is being able to tune each decoder’s output to a specific engine
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
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 spee
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
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
Thanks to all who replied. Your comments/suggestions have provided me with a bit more insight on this subject. A bit of info. as to why I enjoy operating at prototype scale speeds. I worked from 1972 till 1987 for the Soo Line as a Sectionman. Spent 1,000’s of hrs. observing switching, both yard and industry. Any thing faster just does not appear “right” to me. I can put up with my unballasted track, tolerate my wood and cardboard mock-ups of future buildings, even run the GP-30 without the shell-- it’s all good. But let the GP-30 shove a cut of cars into an industry too fast, or jerk when taking up slack and I freak out. Thanks again!!
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.