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The Electronics.

Although I started out with very simple electronics, this was deliberate, it soon becomes obvious that there is a basic level of electronics required for functioning. This is the Electronic Speed Control (ESC). The next stage up is Radio Control, (RC). And finally Semi Robotics, (SM).


Electronic Speed Controllers.

These come in two forms. The "Brushed Motor" and the "Brushless". The former is used for DC systems and the latter for 3 phase AC. Some thought should be given to the amount of cooling that the ESC has available. Coming from a more comfortable climate I was brought up to always force air cool electrical equipment. I normally glue a small 12V CPU cooler to blow on the cooling fins of the ESC using a DPDT main switch. In the case of something like an Mtronicks ESC which has no external cooling fins I then glue on a simple T022 set of cooling fins, in this case a set with 20mm fins is more than adequate.

In a Brushed Motor system the supply is DC and there are four FETs (Field Effect Transistors), that supply current to the motor. This is normally referred to as H drive. The motor sits in the Bar of the H with the four FETS forming the four Uprights. Switching on top left and bottom right causes the motor to turn clockwise, similarly switching on top right and bottom left causes it to reverse.

The rate of rotation is normally down to the technique known as Pulse Width Modulation (PWM). Here a constant voltage is switched on and off at very high frequency. This is used to set the amount of pulses during which the voltage is connected to the motor. This is seen by the motor as a variable voltage. Thus in a 12V line 50% of the pulses being "on" equates to 6V seen by the motor.

Various suppliers offer differing rates of switching. Is there an advantage to different rates? The answer is both yes and no.... High frequency switching is good at high speed and has been shown to increase battery life however some people find the noise from this to be objectionable. Typical rates are between 2,000 and 32,000 Hertz. Low frequency switching has been shown to increase the torque of the motor at low speeds. But there is some obvious vibration induced into the motor by the switching. Low speed rates are 200 to 1,000 Hertz.

Electronize supply an ESC with variable rate from 200 to 2,000 Hertz dependant on "stick" position. Dimension Engineering supply three ESCs running at 32Khz with the capacity to use regenerative braking to re-charge the battery.

Brushless Motor ESCs may be classed as a half way house between an AC invertor and a variable frequency generator. The ESC produces a AC wave form from each of its three outputs. This is then sent to the motor which has a fixed number of stationary coils with a rotating ring of magnets. The wave form produces a series of North and South poles in the stationary coils that the magnets follow driving the ring around. The rate of the rotation is dependant on the frequency generated by the ESC. To reverse the direction of rotation just requires a 2-pole relay to reverse any two of the motor connections.

  • Mtroniks
  • Many other makes sold for the aircraft or drone market

Radio Control.

Currently we are in a change-over period from using the Model Aeroplane style stick controllers to the dedicated Model Loco controllers. At the loco end very little is different. A receiver picks up the signals from the transmitter and either raises or lowers the potential of a line. This is taken by the ESC to be a "stick" position and it either increases speed or reverses. The ESC will normally have a BEC (Battery Eliminator Circuit, a dedicated 5V supply) to the receiver but some people like to have an independent battery supply especially if their loco generates its own electricity.

At the user end things are very different! Modern systems use 2.4Ghz and a "prefix" code to all the channels. Each transmitter has its own prefix thus in theory there can be any number of users on the same frequency and there are hundreds of frequencies to use. This code is called the "BIND". This is also one of the great weaknesses of the 2.4Ghz system. To set up the receiver the transmitter must pulse the BIND code and the receiver set to detect it. This can be done manually by inserting a shorting plug or by the receiver simply using the first BIND signal it finds.... It can take several attempts to successfully BIND the receiver to the transmitter.

The 2.4Ghz system has eight "easy" channels to use, this may be extended with multiplexing to rather higher numbers! This would allow it to be used for point control as well as signalling. It is now possible to have one controller that can be used for 12 locos, but you have to select your loco. Alternatively you can use the eight channels available and dedicate a channel per loco. The former has more functionality but the latter has faster control of a limited number of locos... The common transmitter uses 4mW and has a range of about 15m, the high power one is 100mW and as yet an unknown but VERY long range... I have two self-built 2.4GHz transmitters, each of which can control three locos.


Semi Robotics.

This sounds futuristic but is not as far fetched as it sounds... It is possible to obtain IR detector modules that can be used to prevent the loco from crashing into the buffers or another loco. Sound cards are another example. Some can be programmed to mimic various steam loco sounds or diesel engines. There is a mechanical "chuffer" that will puff smoke slowly or vigorously in response to the "stick" position. Another type has a fan to mimic diesel exhaust blasts. Horns and whistles can be blasted by line-side actuators, magnets, or IR reflective tape on the sleeper.

Sounds.

Loudspeakers.

Most people are happy with the simple loud speaker that comes with the sound kit. Others are not! There are several ways to improve the quality of the sound coming from your speaker. An oval speaker holds both low notes and midrange notes better than a conical speaker. Some form of "baffle" which the speaker is mounted on will help. This can be one of the following:

  • Open Baffle, a plate that the speaker is mounted on.
  • Infinite Baffle, a sealed air tight box.
  • Port Loaded, a vented box.
  • Bass Reflex, a length of tube that projects from a port into the box.
  • Iso Baric, a sealed box has two speakers both working in tandem in the same box with a slight air tight gap.

The Humble Coupling

Probably the least glamourous appendage to your new loco or rolling stock is the coupling....an essential but "fiddly" item to assemble and fit!

Dealing with British "steam era" scene, there were four main types of coupling employed on the main line railways. The London Underground, other electric railways and industrial lines employed a variety of semi-automatic and/or permanent coupling which are not available in kit form, so are not covered here.

1) The Three-link which was used on freight wagons without continuous braking (no vacuum or Westinghouse brake)

2) The Instanter which is a modified 3-link where the centre link can be rotated to provide loose or close coupling (principal users were the Great Western)

3) The Screw Coupling, which was the most common type fitted to both passenger carriages and freight vehicles fitted with a continuous brake.

4) The Buckeye, fitted exclusively to "Pullman" cars and LNER "Gresley" gangwayed (corridor/vestibule) stock, in conjunction with the Pullman type gangway connection (as opposed to the British Standard connection used by other companies). This later became the standard coupling fitted to new coaching stock built to BR "Standard" designs but with a feature which permitted the buckeye to be swung down, exposing a simple coupling hook which permitted coupling to locomotives and older stock fitted with "link" couplings.

When it comes to Gauge 3 stock, the principal suppliers of the various types of coupling are:

Garden Railway Specialists (Three-link, Instanter and Screw)

Slaters (Three-link and Screw)

Walsall Model Industries (Three-link and Screw)

Williams Models (Three-link and Screw)

KayDee industries (Buckeye)

Descriptions of some of the available kits and their assembly can be found at Coupling Reviews.

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Page last modified on March 20, 2018, at 03:49 PM