[Doug]

There is no relation between "maximum number of cabs" and "maximum number of locomotives to be controlled"

The cab is the controller, fixed or handheld. Each cab can control multiple locos - either by switching between locos using pre-assigned buttons or by calling-up the loco in the normal way.

Sometimes it is helpful to have a number of cabs so that you may use a separate cab for separate locos running on the layout. Also, you may wish to invite your friends around to run the layout together. It's great to give each driver his own cab.

 

[Doug]

QUOTE (Gary @ 26 Sep 2005, 13:30)...Now the next bit of jargon is "mu capabilities". When I see this what does it mean and how important is this feature in a system?...
<{POST_SNAPBACK}>

My Arnold system calls it "MTD" for multitraction. I can combine up to four locos, pulling a train together. The central control supports 10 MTRs with their own single addresses.

 

[Doug]

On rotary encoders: Yes they are better as when you switch between locos, you pick up the current speed of the loco without any problem. Your LCD read-out displays the speed of the new loco and the rotary encoder allows you to increase or decrease from that exact point.

Compare this to the ZTC 511 system that has a linear (albeit on an arc) controller. When you switch between locos, there will be an adjustment required to synchronise the controller with the current speed.

 

[Doug]

To address your points in order:

1. You can't have DCC and DC control at the same time. There is nothing to stop you installing a double-throw switch to switch between DCC and DC, but beware of point decoders and other modules if you have them. I don't think they would like DC current fed from the DC controller. It would be best to isolate those too if you have them.

Using DCC, you can usually have one non-DCC loco on the track, controlled with address '0' by the DCC throttle controller.

2. Consists. The DCC controller has to gang the consist locos together so that it can control them with one address. Your consisted locos will then behave as one, called up by any controller on the network by the consist address.

3. BUS. Yes, it's nice to have one so that you may add modules for expansion. I We're talking started with one controller - I now have 5 all linked together and will probably add 5 more if my 'World Domination' plans work out.

4. Computer interface. Remember there will always be people who want this. That's the way it is. I personally think a model railway loco should be controlled with a cab control from the side of the table, but each to his own. I have a computer in my track room, but for the moment it's used to listen to Internet radio. Computers do take the hassle out of complicated and complex layouts. You can program routes, automate sequences and work to schedules that flash up at you - just like they do today in the real railway world. You can have your detailed loco database link up to your control system and using a feedback system, you could theoretically control it from anywhere in the house.

5. Brands. Hornby DCC system and it's XPRESSNET are hot topics right now. This is a communication BUS that is set out and designed to a specific protocol. Other companies' products that also use the XPRESSNET or XpressNET BUS can be theoretically linked together. Companies that use XpressNET include: Atlas, Lenz, ZTC Controls, Arnold, Roco and now Hornby.

Loconet is another type of communication protocol. Loconet and XpressNET are not compatible. Companies that use Loconet include: Digitrax, Uhlenbrock, Fleischmann and a few smaller manufacturers.

 

[Doug]

Back EMF (electromotive force) is a voltage that is generated by the electric motor due to movement between the armature of the motor and the external magnetic field. Measuring this voltage allows you to very precisely measure motor speed and position.

QUOTE (http://www.acroname.com/robotics/info/articles/back-emf/back-emf.html)Typically a motor takes power in the form of voltage and current and converts the energy into mechanical energy in the form of rotation. With a generator, this process is simply reversed. A generator takes mechanical energy and converts it into both electrical energy with a voltage and current. Most motors can be generators by just spinning the motor and looking for a voltage/current on the motor windings.

When doing Back-EMF measurements for motion control, this fact that a motor can also be a generator is exploited. The motor is run almost continually as a motor with current being supplied to turn the windings. Occasionally, and for a very short period of time, the process is reversed. The windings are allowed to float and the inertia in the motor keeps it spinning while a measurement of the voltage from the spinning motor/generator is taken.

The voltage observed when the motor is spinning is directly proportional to the speed the motor is running. This fact can be used to "peek" at the motor's speed with no optical encoders or other forms of active feedback.

Normally a decoder just sends out a voltage to the motor and the loco moves accordingly. With Back EMF DCC, the decoder can determine the speed of the motor - that might be under strain as it goes up an incline, or going faster down the other side - and can adjust the output voltage in a way that keeps the loco going at a constant speed. Adding move voltage to the motor up the hill and reducing the voltage down the hill.

Back EMF does help the loco move at slow speeds too without stalling.

I've always found constant speed settings in model locos a bit strange as it is normal for any vehicle to struggle up a hill a little. Modern cruise controls in cars send more gas to the motor and perhaps down-shift to maintain speed up a hill, but old-fashioned steam engines never had cruise control and it looks good when the model slows to go up an incline.

 

[Doug]

You definitely don't need to learn it all before you try it out, hey I used to test batteries by licking my finger, touching one end, then sticking my tongue on the other end. Now I know better. I learnt the hard way. Take it one step at a time - but don't lick the rails