See also Analogic automation for automatic control of an analogic railway.
Command basic principles
It exists mainly two manners to control garden railway trains:
- Through track, while modulating voltage or sending a coded signal like DCC which give orders to locomotives and accessories. This kind of equipment not being specific to garden trains is fairly well documented and I shall not discuss it here.
- By radio
I first invite you to have a look on the wikipedia page where I have authored the control schematics.
The present page is only about radio control of battery locomotives and live steam locos.
First, it is needed to remind basics about radio frequencies bands used for train control.
Modulation and coding
Before transmitting information, radio signal shall be modulated through a few ways:
- Amplitude modulation - AM - The simplest to build, but with low reliability and less range.
- Frequency modulation - FM - A bit more complex to build, with better noise immunity.
- Frequency Shift Keying modulation - FSK - adapted to digital signal transmission. This kind of modulation is used to transmit data, notably for alarms and garage doors. It shall also be used for industrial data transfer.
Modulations allow transferring rough signal. While transmitting digital signals, it is needed to define a coding.
In order to improve the reliability of model R/C data transfer, PPM and PCM coding are used.
For alarms and garage doors, it exists hopping key coding to kept orders safe. The most used coding is the KeeLoq.
Frequency bands
A frequency band covers a range of frequencies. Often one band cover a range of 1 MHz. This range is generally divided in slices called ‘channels’. The width of these channels varies depending usage.
The power is limited by local regulations, which varies widely.
Wave length which correspond to the length travelled by a wave during one period decrease while frequency increase. Sometimes wave length is given instead of frequency. So, 2 meters band is the same band as 144 MHz (radio amateur frequency).
It is useful to know the wave length to define the antenna length. The most frequently used antennas are 1/4 wave long. So, a 1/4 wave antenna at 433 MHz shall be 16.5 cm long.
Traditional R/C frequency bands
- The 27 MHz band, generally used in AM modulation is now nearly only used for toys. More than 20 years ago, the development of the CB, often used illegally at very high power, have killed its use in R/C models. Its main advantage is that is is legally accepted worldwide. We can find and the old RCS train control was using that frequency, though with FM modulation and PCM coding, much safer than toy systems.
- 35 and 40 MHz are not legal in France (Beware, UK, Swiss and Belgian rules differs).
- In France, the 41 MHz band is used for R/C, but some channels are used only for aerial models while others are used for terrestrial models.
See also here for band and channels model allocation.
High frequency bands
- The 433 MHz band is used worldwide for short range equipment like alarms and also for data transmission. The most frequently used channel is 433.92 MHz for alarms. Power is limited to 10 mW.
- Europe have defined 868 MHz band as being preferred for short range equipment. Power is generally around 1 mW, but the maximum is 10 mW for alarms and 25 mW for unspecific use equipment (Is that also valid in UK ?). One of the advantages is that a 1/4 wave antenna length is 7,4 cm. Generally speaking, range is better than with 433.92 MHz Equipment.
- 915 MHz band is prohibited in Europe. It was used by some train controls. Its usage in the USA is the same as 868 and 869 MHz in Europe.
- 900 and 1800 MHz are only for GSM mobile phones.
2.4 GHz band
- 2400 MHz (2.4 GHz) band imposed itself in R/C models with Spektrum equipment from USA. This band being already fully crowded (this is one of the WiFi band), regulations bodies made some difficulties to accept it in R/C and created local requirements (notably maximum power) not always respected. The power was limited to 100mW in France for R/C commands (what in UK ?). The specificity of Spektrum equipment is not only its frequency band but more the fact that it is jumping from one channel to another if the used channel is too crowded or noisy. It could swap channel multiple times per second. This drive to an unknown reliability in R/C world. The data protocol and jumping is specific to this manufacturer. Following Spektrum fast success, others R/C manufacturers are now proposing 2.4GHz equipment with different and incompatible protocols while Spektrum have licensed a few other manufacturers. We can find low cost Chinese equipment (Turborix or others) in 2.4 GHz but it seems that power could be unlegal (too high) and it is not certain that it is using ‘frequency jumping’. The new garden train RCS control system is using this frequency with the spektrum DSM2 protocol.
The absence of quartz on 2.4 GHz radios and the fact it is no longer needed to handle frequencies during meetings have helped the fast rise of such equipment. The high frequency also greatly improves transmission through obstacles (tunnels or metallic locomotives).
Battery locomotives
Dedicated transitter commands
- USA company Aristocraft (closed in 2013), after having been one of the first to propose track analogic train radio control with ‘Train Engineer’ system (TE), was proposing a 2.4 GHz system intended for battery powered trains. It had named it in all modesty ‘Revolution’. European and North-american equipment were differing due to homologation regulations.
- USA Airwire and Locolinc equipment are not legal in Europe.
- Australian company RCS was proposing a control system with a reduced size transmitter on frequency band 27MHz with FM modulationa and PCM coding. This equipment is described here is now abandoned. The 27MHz band is legal worldwide.
- In UK, Timpdon electronics proposes equipment in 433.92 MHz with reasonably sized transmitters and a carefully designed system. He is an artisan who built equipment on demand and refuse to sell outside UK (while the frequency used - the alarms one - is recognised in most countries).
- English supplier Cliff Barker propose a very simple system based upon alarm keyfob.
Commands with classical R/C transmitter
If the weight and size of a traditional R/C transmitter don’t rebuff you, it exists modules which shall be installed downstream the R/C receiver. Those modules are not only speed regulators but could (for some) handle front and back light, a sound board with bell and whistle. They are supplied by:
Live steam locomotives
Live steam locomotives being generally built in metal are more problematic than others for radio control. This have driven to quick adoption of Spektrum equipment, who is now proposing a relatively low cost radio DX5, sold 100 Euros with transmitter and receiver and no servos.
RCS company having abandoned its live steam module SD-10, remains for those who are reluctant to use bulky classic R/C transmitters: