Layouts need to:-
Give reliable running.
Be easy to understanding and operate
Any faults should be easy to find
A Model railroad design guide
The aim is to supply power to the motor at all points of the layout given that the engine is able to pickup power from the rails i.e. clean wheels and track and track laid without hollows and bumps.
1. Connecting power to the rails.
Use drop wires (light, solid) soldered to the outside of the rail and through a hole to the underside of the layout where they will pick up a power buss wire.
The drop wire could connect to brass or copper strip soldered to the bottom of the rail.
Make one connection to each flexible section or solder joiners to the rail and put loop wires across junctions.
2. When correctly connected the engine goes forward when the positive supply wire is on the right hand side rail.
3. On a large layout the power may be supplied through switches to areas or blocks of track that are isolated from adjacent blocks thus 2 trains can run on the track and be isolated from the power so that they don’t both move together.
If both trains are to be run independently then another motor controller has to be used and the blocks switched to select which one is used. In this case there would need to be three running blocks so there is an overlap and 2 trains never can be powered by the same controller. If multiple controls are used then blocks should be isolated in both rails...there is no common rail.
Points make the wiring more complex but can be used to direct the power and isolate spurs etc so that separate switches and blocks are not needed
1. Simple power switching (typical of hand made points) there is no insulation at the frog, The throw bar is isolated from the stock rails. It needs a large gap at the blade rails to stop wheel back shorts. Note the switched out leg has wrong power so needs isolating gaps after the frog, if the following track is also to be powered.
2. All live, maintains power to all tracks. insulated at the frog, it may have internal jumpers round the frog. It needs a switch to power the isolated frog rails. The blades are safe for wheel contact. Blade power is from rail blade to stock rail contact.
3. Points modified for safe DCC working. The hinges are jumpered, stock rail wired to its blade rail. Frog supply is from a switch supplying power from the correct stock rail. The frog is isolated.
4.Modified power switching with insulated frog (peco) the short unpowered frog section can be a trouble. The frog is isolated non active track, may be plastic.The blade is not powered except through contact with the stock rail. The non selected rail is not powered.
5. Special types that need switches or relays to route power. Can protect against point jumping or allow heel power feed. A tortoise point motor is good for this switching.
There are two common types of motor.
A. A geared low power motor that moves a lever aconnected to the point link bar.
The movement is realistic and the power is supplied to the motor all the time which keeps the point rails pressed tightly to the stock rails. A switch can also be incorporated in the mechanism which can be used to directly supply the frog power or pick a relay.
B. A dual solenoid actuator that flips between the solenoids when a high current pulse is supplied. The power must be removed immediately it flips else the coils burn out. After the pulse has moved the points the power is not present in the solenoid so the over center spring that is in most points holds the track contact.
A Capacitiive discharge power supply (CD)is used to provide a high current pulse from the charge stored on a capacitor. Power then drops down to zero. A center-off switch is needed to connect the power out of the CD unit to the solenoid coil. The power supply then recharges the capacitor, about 1 second is needed for this, until it is ready again.
C. Using a servo motor, available now. While the motor is small it does need electronics to drive it and supply the voltage that it needs. It moves the points at a moderate speed with no noise and looks realistic.
Reversing loops or Wyes
There are three ways to do this
stop in the Loop and change CAB polarity and the toggle the Loop switch.
drive through, automatic with electronic sensing of the train position.
Use electronic frog power switching
Which one to use depends on the layout and complexity of the loop.
How to wire a simple loop.
The points can be any type but must be isolated from the Loop rails.
Power the Loop from the change over switch, stop when in the Loop,
change the points, the CAB direction, and the Loop switch then go.
If the switch is incorrect there will be a track short when you cross from Loop to the Main track.
b. Feed the loop from a bridge rectifier (small power loss) The switch selects the direction the train runs while in the Loop. CAB direction and Points can be changed at any time while in the Loop without having to stop. If the switch is incorrect there will be a track short.
power packs, controllers, cabs
These range from simple battery/rheostat setup to complex pulse types with constant speed control.
1. A Rheostat (variable resistor) that reduced the power/voltage to the rails. Note the motor jumps at start up as its resistance changes when running.
2. Electronic rheostat (transistor) maintains a more regulated voltage and ignores load changes better. Still tends to start fast then have to be slowed down
3. Pulsed power - the rate varies to vary the speed. some use up to 20 volts pulsed to the motor. This amount of power can effect the life of the motor. A pulse of lower voltage 10 - 12 is safe. It enables a slower more controlled start. Some pulse controllers only use a pulse at low speed and reduce it to become pure DC at higher speeds. It is still effected by load changes such as hills.
4. Use feedback to monitor the motor speed as the load changes for hills and inclines. This controller sends a pulse; and then in between pulses check the voltage generated by the motor which is a measure of the speed. The next pulse is adjusted to compensate for any slowing or speeding up.
Electronics that you may add
1. block detectors - detect the presence of rolling stock etc. over a large length of track. The engine is easy, rolling stock is harder as each wheel set needs a resistor wired across it.
Usually using a current sensing circuit and diodes in the power feed that give a voltage drop when power is used by the motor or through resistors on the wheel sets. This produces some loss of power to the motor. Relay points output or a transistor switched to ground.
2.There are some types that use a high frequency signal detector. These do not reduce the power to the motor but do need special circuitry to stop the high frequency being damped by the power supply/power pack. The detector is tuned to the imposed frequency.
3.Most practical is a transformer coupled to the track power input that detects the presence of the DCC signal when a train is in that track section. There is no track power loss.
4. Spot detectors - usually used to activate some function as the train passes i.e. crossing lights. There are several types
Magnetic reed switch - need a magnet on each engine
Photo cells - visible light types need ample light on the detector and careful adjustment
Infra red emitting LED and detector. Light is sent up to the underside of the train as it passes and bounces back down to a detector diode between the sleepers
Short section of isolated track triggering an optical isolator (Opto coupler) which gives an output when a loco wheel set bridges the isolated rail and running rail. Needs the motor power to work.
A can-do item when you get more experienced
Signal systems can vary from simple stand alone signals that change when a train passes to complex inter-locked sets that work through block detection, points switches etc. Block power can be controlled from the signal so that if signals oppose the train the power is cut off and the train will stop if the block ahead is occupied. Three aspect signalling is not very realistic unless the operator can see the signals and slow for a caution. Also the train will stop unrealistically and jump start again unless some special circuitry is used to control the restart or the operator reduces the track power and then restarts manually.
Signalling on a large layout can also be used for route selection at loops and through yards etc. basically you nominate the start and end point, which activates the signals and points until the route is established.
Items such a station stop, signal stop and shuttle modules are available.
Layout computer control is available but needs programming to the layout. DCC control would be best used allowing you to control a station with loop tracks to allow 2 trains to pass.
An example of inter-station stand alone signalling.