I have used the electronics from cheap radio controlled 'toy' cars to provide remote control for my battery locos and for track power control. (ie for track power, the R/C unit controls the voltage applied to the track. This means you can control your train while walking around.) These can be bought for $A20 to $A40 at Big W or Dick Smiths.
I am also using 433 MHz UHF 'car door' type remotes ($23 from Oatley Electronics) for radio control, along with PICAXE programmable controllers to control motor speed, direction and do sound as well. Click here for details.

This description may be of use to those who are electronically minded. They will not allow a novice to build them. The following is a general description of the toy car types, which may allow you to design your own. It's hard to be specific because the toy cars are all different.

I have used two types -
A. Those that have two 'sticks' - one up/down and one left/right. These have 4 functions (sometimes refered to a 5 functions on the box - they count 'stopped' as a function!)
B. Those with only one stick.

A minimum of 3 different commands is needed to control a train - 'Power', 'Brake' and 'change direction'. If 4 R/C functions are available the actual direction can be selected specifically (eg stick right=forward). If only 3 R/C functions are available it is imperative that the loco has headlights so you can see which direction is currently selected.
In both cases the Up function is 'Power'; the down is 'Brake'. ie when the stick is held up the loco will accelerate (slowly). When the stick is released, it will continue at the same speed until the brake is applied. The Brake can be held down to reduce speed and if released the train will continue at the new speed. If held long enough the train will stop.

The R/C cars usually have 2 motors (4 wires) and it just a case of converting the voltages that appear on these wires with the different signals, to what we need. The basic part of the power controller is just a usual Inertia capacitor and pulse power controller as used in many non-R/C controllers. We just have to charge/discharge the Inertia capacitor and pick up or drop out a reversing relay. eg find the wire that goes positive when the stick is up and use it to charge the Inertia capacitor (Power). You will probably need to use a comparator to level shift the voltage between the R/C (usually 6V) and the power circuit. Similarly, use a wire that goes low with stick down to discharge the capacitor (Brake)

I use a standard reversing relay to change the polarity to the motors. Sometimes I get fancy and put in checks to ensure that you can't change direction unless stopped. I have used flip flops either in set/reset mode where there are 4 R/C functions available, or D (toggle) mode where there are only 3. Or I have used a capacitor to remember the direction and charge/discharge it, and then a Schmidt trigger to determine whether it is charged or discharged to drive the relay.

The controller with only 2 R/C functions (Up/Down) uses a different approach to reversing. Direction is changed by applying the brake when the train is stopped. Each time this is done the direction changes.

Here are two typical schematics - email me if you want more info.
track power controller circuit    Battery loco controller

I have used a simple discrete component, sound system which needs a wheel cam to drive the chuff (it's based on a Silicon Chip article).
I am also using PICAXE programmable controllers to do diesel and steam sound. Click here for details on this circuit.

The component circuit uses a reverse biased transistor to make white noise, which is than shaped each time the cam closes to give a good chuff sound. Note that you need at least 9V for the white noise generator to work, so running this from a 9V battery is a bit 'iffy'. Schematic
The shaping is done using a diode (D4 in cct) in the feedback path of an opamp amplifier. Varying the current through the diode, varies its resistance and thus varies the gain of the amplifier. (low current=low gain) The diode current is set mainly by R4. The 'attack' time of the chuff sound is set by the timeconstant R3C3 and the 'decay' time by R4C3. Making R3 smaller (100k) gives a 'harsher' chuff sound as if the loco is working harder. (Choose R4 first for max volume, then C3 to give a good decay time, then R3 for the required attack time.)

The diode current also depends on the voltage driving R4. This is derived from C2 which is charged to 12V whenever the power is applied (from the R/C controller). It is discharged when the brake is applied, with a time delay. This means the volume is max when you apply power, and reduces when the brake is applied, down to nothing after the brake has been on for a few seconds. There is always a quiet, constant hiss, even when stopped, due to the inherent diode resistance even with no current.

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