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Last Updated March 18,2019

Radio control of locos using model aircraft 2.4GHz equipment.

Introduction      Transmitter    Receiver    Motor controllers    Binding   
Direction control    picaxe controller    Tx modifications.

A whole range of RC equipment is available for model aircraft fliers, based on 2.4 GHz technology. As many model planes are electric these days, the equipment is ideally suited for controlling our locos !
Previously, the cost has been excessive, as model planes require more 'security' and range than we do. But now a cheap range of transmitters/controllers is available, which allow a loco to be radio controlled for under $A70 (incl postage). Including 18, NiMH batteries from Hobbyking, (see later) the total will be less than $A100. (say 55GBP)
If you need a battery charger, that will be an extra one-off cost.

2.4 GHz is virtually interference free and there are 4 billion different channels !

NOTE: If you don't want to use the bulky, plane type controllers, RCtrains (UK based) supply a great range of small hand held 2.4 GHz controllers for model trains.
click here for their webpage

Hobbyking has warehouses in UK, Australia and US, so the postage rates are not too bad. I have compared prices for UK and they seem to be about the same for the exchange rate. I've used AUD here, but on the Hobbyking website, just select your currency.

For a simple speed and direction control, this is what you need to buy from Hobbyking :-
* HobbyKing 2.4Ghz 4Ch Tx & Rx V2 (Mode 1)(THROTTLE ON THE RIGHT) about $A30 link
* TGY-20A Turnigy 20A BRUSHED ESC (electronic speed control) about $A7 link
* Turnigy TG9e or TG9 micro servo about $A4 link

NOTE - There was a Version 1 Tx and Rx. These have been replaced by version 2, but this makes no difference to the following description. Just make sure you always get Tx and Rx of the same version!

In addition, you will need:
* eight AA batteries for the transmitter, (can get from Hobbyking)
* a DPDT switch for reversing and
* a bit of scrap styrene or brass about 30x30mm.
And of course, the batteries for the loco.

Transmitter (Tx)
The Tx is a 4 channel unit, but we'll only use 2 initially. It has 2 joysticks, each of which can move up/down and left/right. This is a 'mode 1' Tx which just means the right hand stick does NOT spring return to centre as the other 3 movements do. It's used for the loco speed control (throttle). It also has 4 'fine adjustment knobs - set them to centre position and leave them!
The 4 channels are labelled:-
RUD = Rx channel 4 = left stick, left/right movement.
THR = Rx channel 3 = right stick up/down movement.
ELE = Rx channel 2 = left stick, up/down movement.
AIL = Rx channel 1= right stick, left/right movement.

Across the bottom, there are 4 'servo direction' switches with REV and NOR positions. Set the THR to REV and the others to NOR. (no good reason for the throttle to be REV, it just has to be to work!)

I used the left stick right/left movement for forward/reverse, but you can use any of the 3 besides the throttle.

Transmitter batteries
You can used non-rechargeable AA cells if you want. Or you can use NiMH (nickel metal hydride) or NiCd (nickel-cadmium). The Tx has a recharging jack on the side. If you want to try rechargeables, you can get from Hobbyking at the same time as you buy the other stuff, for around $A2.50 a cell. link here

Receiver (Rx)

The receiver has a set of 7, 3-pin sockets down the side - 6 channels (we only have a 4 channel Tx, so only 1-4 work) and one labelled Bat (battery). These are for plugging in the servos or esc. NOTE the 'outside' pin (right in the pic) is always the negative (black or brown).

The motor speed controller (ESC=Electronic Speed Control)
This is rated at 20 amps - more than we'll ever need. (You can buy the 30A version if the 20A is out of stock - they are the same size and cost about $1 more). But a max of 10 NiMH cells = around 13V max.
It's shown here plugged into Ch3 (throttle). As the stick is pushed up, more volts are fed to the motor.
It comes with an instruction sheet, so read it! It has 2 small plugs at the motor end to select if you are using LiPo or NiMH batteries, or whether you want a brake applied to the motor when the throtle is set to zero (NO).
According to the Data sheet, the speed controller above can have a max input of 10, AA cells, so your loco can only have that many, maximum. I've never found 10 a problem with my Bachmann or Aristo motors, but maybe LGB needs more volts ? I have used 11 and others have used 12 cells without damage. If you're using LiPo batteries, you are limited to 3 in series (=12V).
Note that it has a 5V output to power the Rx which is fed back along the same 3-core cable, so no extra power wiring is needed. (also no need to plug anything into the BAT socket on the Rx.)

Binding

Now we have to BIND the transmitter to the receiver.
This is just telling the receiver which transmitter it should ‘listen’ to. It’s like the olden days of selecting a different crystal channel, except it’s all automatic. Each Tx is manufactured with a different code or channel. – there are 4.2 billion different codes – so the chances of there being 2 transmitters with the same code in the same place are pretty small. Binding just programs the Rx to know its transmitter’s code. You only have to do this once !
There's no Instructions included, so here's the step by step:-
* Plug your ESC into servo channel 3 of the Rx, as shown above. The black or brown wire (0V) goes to the right in the pic above. This is just to provide the 5V supply to the Rx.
* Put the provided ‘binding plug’ in the BAT socket of Rx. (this is just a wire that joins 0V to the sig wire in the BAT terminal.)
* Apply battery to the ESC. You should see a red LED blinking on the side of the Rx.
* Now hold down the Bind-Range-Test Button on the Tx , and turn the Transmitter on. After about 3 to 10 seconds the Rx LED will stop blinking and go steady.
* Remove the binding plug while power is still applied to the RX .... and that’s it.

NOTE: That was the only time you will ever turn the Rx on before the Tx.
Now you will always turn the Tx on first, then the Rx
HINT I have found that binding will sometimes not work if another Hobbyking transmitter, that is turned on, is nearby. So if you have trouble 'binding' make sure you are at least 5m away from another Tx, or turn it off.

Direction control
This is where you have to do a bit of work.
Here's the DPDT switch you bought.

This is the servo with some of the typical attachments that fit on the white splined shaft. The shaft rotates 45 degrees one way with the stick up (or right) and 45 degs the other way when you push the stick down (or left). It then returns to its central position when you release the stick.

Now you can epoxy the switch to the servo as shown so the centre of the Sw is in line with the servo shaft. (I've just used a rubber band for the pic).

Now you have to use trial and error to make a 'plate' to attach too the servo arm (I use the one circled in red above) to knock the switch over when the servo operates. It's roughly the shape shown in red (don't forget the bit hidden under the arm, and is about 40x20mm. It has to be a wide at the switch arm as the length of the arm travel from one position to the other. I attach it to the servo arm by just twisting a couple of bits of wire, shown orange.

You solder wires to the sw terminals as shown in the pic which is the underside of the switch.
Now plug the servo lead into the Rx channel 4 (left stick, left/right ) and try to operate the switch. You'll probably have to adjust the arm position and file a bit of the cam to get it to work.

And that's it. Turn on the Tx, then the battery to the motor controller (and therefore the Rx) and try to control speed and direction.
There's still 2 spare channels, which I have used for Volume control and whistle. But that's a future story.

If you want to control more locos using the one Tx, that is possible. You either only turn one loco on at a time, or you can turn 2 on and double-head! All you need to do is buy another motor controller and servo as above, and another receiver link here for $A15. So to control another loco will cost about $A60 incl batteries and postage.

Loco Batteries
You can buy AA, NiMH cells from Hobbyking - see link above.

For more info on NiMH batteries and charging see my link here.

Replacing the ESC with a Picaxe interface to Receiver

To overcome this ESC voltage limitation of around 15V MAX, I tried converting an old track power controller. As the old controller had a 30V supply, I couldn’t use a stock ESC, so I built my own using a Picaxe microcontroller.
The old track controller was an inertia type with Darlington transistor, ‘pure’ dc output. It was an easy conversion as I could reuse the main power transistor part of the old controller. I just had to decode the ‘servo’ pulses from the Rx throttle channel and convert them to a PWM voltage signal and feed it to the inertia capacitor.

The Picaxe 08M does this easily-the prog is only 100 bytes. The PULSIN command measures the length of the ‘servo’ pulse and the PWMOUT commands runs in the background. I incorporated standard features in the program of auto-zero-ing at turn-on; and 3 sec time delay if signal is lost before the motor turns off. To reverse, I used my now standard micro servo with a SPST switch superglued to the side. The switch just operates the existing reversing relay.
Because we're not using an ESC we have to provide a 5V supply for the Rx, servo and Picaxe cct. This has to be a pretty 'hefty' supply as the servo takes half an amps when stalled. I used an LM7805 and HAD to use a 4700uF capacitor on the 16V input to get it to work - a 2200 uF didn't work!

Here's the block diagram:


If I hadn't been reusing the old stuff, I'd have just fed the PWM pulses from the Picaxe into the gate of a power MOSFET, just as for a loco.

Mode 3 transmitter conversion

The Tx I bought are called Mode 1 – this just means the right stick is the throttle (no spring return). Mode 2 has the left stick as throttle and is used more in USA. I have converted my #2 Tx to what I call Mode 3, where both left and right sticks are throttles.
This is achieved as follows: (My thanks to Bill Wray from Texas for these notes and pictures).

1. First, remove the 4 screws holding the back cover on the remote transmitter. Lift the cover part way off and unplug the power leads from the circuit board. Set the back cover aside.
2. You will see on the left joystick a shiny metal wiper arm which rubs against detents in the throttle controller, holding it in place where you left it. On the right joystick, there is spring that centres the joystick.



3. Remove the screw and lift off the spring with long nose pliers spring from the right joystick “up-down” movement.


4. Fabricate a wiper arm from a piece of 6mm wide thin brass. Copy the wiper arm on the other joystick. I made the indent by using a dressmakers pin and hammering it across the brass. Attach the wiper arm, using the screw removed with the spring.


5. Reassemble the remote controller, you now have a controller which will do basic (speed and direction) control on two separate locomotives.