LC302 Locomotive Mounted Speed Controller

The LC302 is a high quality microprocessor controlled speed control unit which is designed to fit inside the locomotive and operate in a number of different modes. In its standard form, the LC302 will take its power from a locomotive mounted battery and its control signal from a radio receiver, but it is possible to  pick up power from the track, or to switch to conventional speed control from the track voltage. The LC302 will work over a number of different voltages and currents, and provides a regulated supply for a radio receiver.

Choice of motor, batteries and radio

The booklet, Battery Operated Remote Control in Gauge O, deals with the choice of motor, batteries and radio.

Voltage inputs

The LC302 will operate from voltages between 3½ volts to 12 volts. If you wish to use higher voltages this would depend on the exact circumstances, in particular the current of the motor - please phone and enquire. In particular, never exceed 20 volts - the unit contains protection circuitry and will blow the external fuse (or internal fuse, if no external fuse is fitted), if it is connected to a voltage higher than this.

Note that the LC302 includes a ‘battery eliminator circuit’, which provides supply voltage to a radio receiver connected to the radio connector. This circuit will provide the input voltage less 0.3 volts up to a maximum of 5 volts. Note that most receivers require at least 4 volts to operate, giving a minimum requirement for 4 ni-cad batteries.

Connecting Up

A standard LC302 installation requires batteries and a radio receiver. There are three sets of leads from the LC302 : a lead with a plug which fits the radio receiver, a pair of wires to the motor and a pair of wires to the batteries. If non-rechargeable batteries, or removable rechargeable batteries are fitted, these should be fitted in a battery box. Otherwise, the batteries should be solder together and a charging socket fitted between them and the LC302. The system is wired up as shown.

The red wire from the LC302 is the positive supply, and should be connected (via the charging socket) to the positive (+) end of the battery. If the battery is fitted with a raised button contact it will be at this end. The black wire from the LC302 is the negative return, which is connected via the charging socket to the negative (-) end of the battery.

The charging socket is fitted in the black (negative) lead between the batteries and the LC302. The charging socket is also connected to the red (positive) lead to provide a path for the charging current. Antenna supplies a charging socket, which is connected as shown. The Antenna socket is internally switched so that the LC302 is disconnected from the battery when the charger is connected to the batteries. If another charging socket is used, it must also be internally switched, as it is vital the charger is not connected to the LC302. Chargers can produce much higher voltages than the batteries they are designed to charge, and these high voltages will damage the LC302. The internal switching on the Antenna socket will only work if it is connected as shown below, so damage may result if this wiring is not followed (looking from the back of the socket).


A useful addition if space is available is a switch to switch off the LC302, radio receiver and motor when not in use. This will prevent the battery being discharged. If you can't squeeze a switch into your locomotive, inserting a blank plug (i.e., a plug with nothing attached to it) into the charging socket will have the same effect. The switch, which can be a single pole on-off or changeover switch, can be in either the red (positive) or black (negative) wires between the charger socket and the LC302. The batteries can be recharged whenever the charger is connected whether or not the switch is on. As mentioned above, if a charging system other than the Antenna charging plug and socket is used, a switch must be provided between the power source and the LC302 and this switch must always be switched off when charging is being carried out, otherwise the LC302 (and receiver and motor) may be damaged.


Ni-cad batteries, and other rechargeable types, can output very high currents should they be shorted out or should a fault occur. Currents of several tens of amps can be generated, which will not just melt but vaporise wires, as well as resistance unsolder your model and generally cause unpleasant effects. For this reason, the LC302 is fitted with a tiny internal fuse, but unless space makes it impossible, you should fit the fuse and fuse holder provided free with the unit. The fuse should be fitted as close to the batteries as possible, while being in a position where it can be replaced. It does not matter if the fuse is fitted in the red (positive) or black (negative) wire to the motor. Wrap the fuse holder with tape to prevent any chance of shorting against other wires or the body. The internal fuse in the LC302 will protect the model from most accidents on its own, but a fuse will not protect against faults between the batteries and the fuse (which is why it should be fitted as near the batteries as possible) and if the fuse on the LC302 does fail, it can only be replaced by returning the unit to Antenna Models. A charge of £1.50 (in stamps) including postage will be charged for changing the internal fuse.

Other connections

A useful precaution before fitting the system to the model is to connect it up on the test bench/kitchen table, and see that it all works. Charge the batteries using a slow charger (such as the Antenna charger) for about 10 minutes. This will run the motor for a few seconds and allow you to check that the radio and motor work correctly.

The batteries should be connected positive to negative, i.e., the positive end of one battery should be connected to the negative end of the next. The red lead from the LC302 should be connected to the positive end of the first battery through the charging socket (as perhaps switch) and the black lead to the negative end of the last battery, with the other positives and negatives connected to form a daisy chain arrangement.

It does not matter which way round the blue and yellow wires are connected to the motor. Reversing the wires will cause the motor to turn in the opposite direction for a given movement in the transmitter switch. However, most transmitters, including those sold by Antenna, have ‘servo reverse’ switches which also change the direction of travel for a given direction of movement of the stick.

The LC302 can be plugged into any of the radio channels on the receiver, allowing it to be controlled by any of the sticks on the transmitter. On a two channel transmitter, the right hand stick (normally channel 1) usually has a left to right movement, and the right hand stick a front to back movement. You can use either of these channels depending on your particular preferences. The speed of the motor controlled by the LC302 will depend on the amount the stick is moved from the centre position.

Each stick has a smaller adjusting control. This is used for fine adjustment of the centre position so that when the stick is released the motor will be switched off, but it can also be used for slow speed control.

Centre Adjustment

There is a small adjusting screw on one side of the LC302. This allows the centre off position of the LC302 to be adjusted to match that of your transmitter, so that when the stick is released and springs back to its centre position the model stops without you having to move the adjusting control from the centre position. This leaves the adjusting control free for use as a slow speed control. If you bought your transmitter and receiver from Antenna with the LC302, it will already have been adjusted to suit, but if not, or if you want to use the LC302 with a different receiver, it is very easy to adjust. Set the unit up on the test bench, and switch it and the transmitter on with the stick released and the adjusting control in its middle position. It is essential that the power to the LC302 is switched off, either by using a switch or blank charger plug, because the LC302 will only look to see the position of the adjusting screw when power is first applied to the unit. With both main and adjusting controls on the transmitter in the centre position, the motor should be off. If not, switch off and move the adjusting screw very slightly in one direction or another, and then switch on again. If you do not switch off and on again the LC302 will not look at the position of the adjusting screw. If the motor runs faster, you turned in the wrong direction, so switch off, and adjust the switch back the other way. The aim should be for the motor to be off, and for it to start moving at about the same amount off centre either way from the centre position. It may take a little tweaking, but only needs to be done once. Remember to adjust the screw by very small amounts (less than 10°).

Always discharge the batteries before fitting them to a model, either by connecting them up to the LC302 system and running the motor until it stops, or by connecting a resistor across them. Never short ni-cad batteries - they contain a large amount of charge and could start a fire or explode if they are shorted. This is why it is essential to discharge them fully before fitting them into the model, especially if it is a brass one. If you accidentally short out a fully charged ni-cad when fitting it to a model you could inure yourself, and/or convert part of your model to a piece of charred metal.


Unless your batteries are removable, you will need a suitable lead to go from your charger to the model. Always ensure you have the correct charger for your batteries. Chargers for lead-acid batteries will not charger ni-cad batteries, and vice versa (in fact, damage will be caused in each case).

The Antenna charger is a slow charger for ni-cads, and takes 12 to 14 hours to charge the batteries. This type of charger will work for any number of batteries up to 15, as long as it is supplied with a voltage at least 2 volts higher than the voltage of the battery (up to a maximum of 20 volts). The charger uses different leads for different battery capacities, since the charging current depends on the capacity and the charger is effectively told the charging current by the lead used. Leads are available for charging all the different batteries we supply, so you only need one charger for all your models, even if they have different batteries. However, you will only be able to charge one of them at a time. Futaba Attack transmitters contain a charging socket and a lead is available to allow these to be charged as well.

The charger should be used with the metal heat sink uppermost. A wire ended lead is supplied which fits the input socket. This lead should be connected to a low voltage supply of less than 20 volts (ac or dc), which is at least 2 volts more than the battery voltage, and can supply a current greater than one tenth of the capacity of the battery. For example, to recharge a bank of 5 1100mAh ni-cads, a supply of between 8 and 20 volts, ac or dc, with a current capability of at least 110mA, is required.


The actual frequency the system uses to transmit the radio signals depends on the value of crystals inserted in the transmitter and receiver. These crystals can be changed as described in the radio instructions. All models should have different frequencies, except that you could use two different channels on one transmitter to control two different models if they both have receivers with the same frequency. In this case the LC302s would be connected to different channels on each receiver.

Running the locomotive from the track

It is possible to connect a double pole switch the motor from track power to battery power. Track pickups will have to be fitted to the locomotive, but when the locomotive is switched to track operation the radio control system is isolated and the locomotive will respond to a conventional track controller in the normal fashion. This is done by connecting a double pole changeover switch between the LC302 and the motor such that the motor is either connected to the track or to the LC302. It is essential to isolate the LC302 from the track in this way for two reasons- the first is to prevent any back feed from the track which would damage the LC302, and the second is to prevent the LC302 from trying to drive the track and therefore the other models on the layout. Even if the track controller is turned off, and no other models are operating, if the LC302 was connected to the track, and live frog points were used for isolating locomotives, the LC302 output will be shorted out because the live frog will connect the two running rails together when a trailing point is switched against the locomotive. The correct switching arrangement is as shown.

When running from the track, the radio system should be switched off to conserve battery power. This could be done by combining the track/battery and battery on/off switches into one three pole switch, although then the only way to switch the radio system off is to switch the track power one, and it is not possible to isolate the locomotive. An alternative is to interlock the switches by soldering a tab on to the track/battery switch so that when it is switched to track, it moves the on/off switch to off if it is not already set that way. When the track/battery switch is at battery, the on/off switch is free to move to both positions.

Any Questions?

Note that further details of battery operation are given in the enclosed booklet. Please contact us if you have any further questions.
Antenna Models Brandon House Bentinck Drive Troon Ayrshire KA10 6HX Scotland +44 (0)1292 310 903