Hi all, I've been contemplating converting to DCC for a while now and am deciding which features suit me best. However I'm a bit confused on a couple terms and wonder if anyone can tell me if I'm thinking right. Basically I've heard about the difference between "encoder based" and "decoder based" throttles but I'm not sure which does what. Here's the way I understand it:
Encoder based throttles use the command station to determine what speed or direction a train would be travling at. I.E. the train speed is derived from the throttle setting. These systems are more prone to runaway loco's unless the loco is brought to a stop before switching control to another unit. If the new loco is in motion when acquired by the command station, a sudden speed change can occur whena new throttle setting is made= runaway loco.
Decoder based throttles accept the decoders current speed setting and makes the throttle relative to the decoder. I.E. throttle setting is derived from train speed. Meaning to me that a train can be allowed to continue in motion while another is acquired and that neither train will display a sudden speed/direction change= no runaway loco.
If my thinking is correct, then I want to have a system that is decoder based. Here's why:
I'm not a big fan of runaway loco's, Being able to take control of another train while in motion can help prevent cornfield meets, real trains don't stop moving just because the dispatcher isn't watching, some switching moves and helper operations are easier when the trains don't have to be stopped to adjust controls...
Along with this clarification, I'm curious as to what systems support which control. It would seem to me that command stations with positive stop knobs would have to be encoder based (Zephyr come to mind) abd that systems that use buttons for speed control would have to be decoder based (Lenz 100) Some could probably go either way and do the decoders themselves make a difference?
Modeling the Cleveland and Pittsburgh during the PennCentral era starting on the Cleveland lakefront and ending in Mingo junction
I can't help you directly with the question as you have phrased it, but I can tell you that I have two encoder throttles, the DT400's, each with two encoder knobs that permit the controlling of two engines per paddle. I have engines from five different manufacturers with decoders from Soundtraxx, Loksound, and QSI. In four years of using my Super Empire Builder and the DT400's, I have never experienced a runaway engine. I have powered up to find one engine creeping along barely perceptibly, but the speed step display on its active throttle shows "01" or whatever I must have left it at. It is simple to turn the encoder to read "00" and the engine stops. It is never "run away", but always completely under control of the DT400 information packet system.
I will be interested in the responses you get from those more knowledgeable than I. Good question!
-Crandell
There are Encoder based throttles and Potentiometer based throttles. Decoders go in the engines and every DCC loco needs one.
Encoders will turn 360 degrees continuously. They work by sending changes of their position to the command station. The amount and speed of the change can be interpreted by the Command station as speed changes. Encoder based throttles do not care what position the knob is in when you pick the throttle up. They only change anything when turned . For this reason if you have an engine being controlled by one encoder based throttle, iof it is acquired by another encoder based throttle, the engine will continue on in the same direction and speed until one of the two knobs are moved.
Potentiometer based throttles work by sending voltage to the command station. The amount of voltage and its polarity are interpreted by the command station as speed and direction commands. e.g. Change polarity- change direction; increase voltage-increase speed.
Potentiometer based thottles work best if the engine is only on one throttle at a time. This is because the pot is allowing a voltage through and anothr pot on a different throttle can be set to a different voltage and /or polarity. The command station gets the voltage from each throttle and sends the appropriate command to the engine. First command to the engine wins. The next command may be from the other throttle and it wil be acted on by the engine's decoder. That can lead to some pretty "interesting" situations.
I prefer encoder based throttles. They are more accurate and can be set at almost infinite settigs depending on the firmware in the command ststion. I also have a potentiometer based throttle but use it only occasionally.
Martin Myers
Hmm ok that makes more sense. Pot based throttles are basically "absolute" the loco takes on whatever the throttle setting is. Encoder throttles, having no fixed zero, can pick up from whatever the current train speed is.
So it sounds like I have my terminology mixed up. So do the decoders care which control is used? I know they're supposed to be compatible but are there any "gotchas"? Or is this completely handled in the command station? Also which entry level systems use encoder throttles? I believe MRC and Lenz100 do but the zephyr doesn't. What about operator cabs?
Encoder based throttles allow much finer motor control. Your question about 'runaway' locomotives really has nothing to do with if the throttle has encoder or pot based throttle. 'Runaways' are usually due to loss of signal on the track. Poor wiring or running DC engines using 'Zero Stretching' on a DCC layout can cause that problem.
I feel that you are 'reading into' the 'techie' stuff too much. Many DCC throttles use encoders. The Digitrax Zephyr uses a built in throttle on the command station that may be a 'pot', as it has limited 'stop to stop' throw. The handheld Digitrax throttles like the DT400 use encoders. The decoder has no idea what kind of throttle or system it is connected to. It just reacts to commands that are sent down the rails. That is why you can use different manufacturer's decoders on the same DCC system. The throttle tells the command station what it wants done, and the command station sends out the proper command to a specific engine(or consist of engines).
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
The Zephyr uses a potentiometer, as does the UT-4. DT400 has the encoders. But Jim is right, the command station does not know and does not care what type of control knob the throttle has. Add me to the 'prefer encoders' group, the control is much finer. With Digitrax (and I suspect the others that have encoders) there is 'ballasitc track' which works like your computer mouse. Move it slowly and you have super-precise control, but it would take a 6 foot wide desk to move the cursor from one side of the scree to the other. So when you want to 'jump' to the opposite side of the screen you move the mouse faster and the cursor moves in bigger jumps. The DT400 works this way (it can be turned off if you prefer) so that if you turn the knob slowly, your train gradually changes speed, one step at a time. Or you can crank it fast and jump from stop to half speed instantly. In short, you have hte option of operating it like a potentiometer control PLUS have the steady fine control the encoder provdes that you just can't get from a potentiometer.
Switching between which loco you are controlling is another place where encoders are superior. Since there are no fixed positions in an encoder (they turn forever in either direction, no stops), there's no matching required, you can switch between two locos and unless you change the speed, they both run at whatever speed they were last set at. With a potentiometer control, since there are physically defined positions, the train speed will adjust to the potentiometer position when you select back and forth. Unless you have the very expensive ESU system, the potentiometers on it are motorized so when you select a different train that is running at a different speed, the console actually turns the potentiometer to match the speed of the train. Typical German overengineering - motors and computer logic to control them when simply using an encoder would have not made it an issue.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
OK the decoders don't care which throttle is used. Encoder throttles aren't prone to the sudden speed changes that potentiometer throttles are unless you're very good at matching or pick one of the points that a pot will match at (zero or full) So encoder throttles for me.
So that just leaves the question of which systems fit the bill. Which ones have encoder throttles for the primary cab and utility cabs?
As has been mentioned, the Zephyr's built in throttle is a potentiometer, but you can use DT400's with the Zephyr and they use encoders. The Digitrax UT4 throttles use a potentiometer, but according to the manual, when you select a loco, "the loco’s speed will slowly match the current settings of the UT4," so you should not get sudden speed changes with it.
NCE's Pro Cab, Power Cab and Cabo4e throttles use encoders, NCE's Cab04p uses a potentiometer, and NCE's Cab05 does not have a knob. The Cab05 uses buttons for speed changes and would not be subject to sudden speed changes.
Lenz does not have a throttle that uses an encoder. Their LH100 uses buttons for speed changes and would not be subject to the sudden speed changes. Their LH90 uses a potentiometer. With the LH90, if you have the direction toggle in the center position when you selct a loco, the throttle's display will show you if the throttle setting matches the loco selected and if not which way to turn the throttle so that you can closely match the throttle to the loco bfore actually taking control of it.
All of MRC's throttle are encoder based.
If you use a fair amount of momentum in your decoder settings, a 'pot' style throttle works fine for smooth starts and stops. I find it nice because you have a zero, a middle point, and a top point for the speed range so you have something to go by when operating. For example I like to run pretty slow, I run my passenger trains at about 35 MPH. So from experience I'll know that a certain engine will need to go from zero to maybe 1/2 full power to reach 35 MPH. Course with a Digitrax Zephyr or UT-4 like I use, I can just set the throttle to 1/2 full power and switch the direction switch fron neutral to forward, and the engine will start up slowly and steadily increase speed until it hits the set speed (thanks to the momentum setting). Turn it back to neutral and engine drifts to a stop.