One remote, several models: how IR channels, red and blue sockets, and tunnels work

When several remote-control models share a room, three rules decide which one moves. A receiver only obeys a remote set to the same channel, from 1 to 4. On that channel, the remote's left dial drives everything plugged into a red socket and the right dial everything on a blue socket. And a receiver has to see the remote's infrared light: if it can't, it keeps doing whatever it was last told, which is why a train that has gone into a tunnel won't stop. Get those three right and a room full of models stops being chaos.

This guide uses the Floor Express, the remote-control locomotive in the starter builds (level 4, about 40 minutes), but the rules are the same for any model with an IR receiver.

What's on the train

The Floor Express is built round a Train motor, a whole motor bogie with two wheel axles. The AAA battery box clicks onto the motor's round pivot, and the IR receiver sits on top of the box as the driver's cab, its dome at the front. The train motor and the LED headlights both plug into the receiver, and the booklet's last step is to pick up the remote and set it to the receiver's channel.

The parts it uses, from the parts list:

• IR receiver: 4 channels and 2 outputs, red and blue, sharing about 800 mA. A channel switch sets which of the 4 it listens to.
• Speed remote: 2 speed dials, each with 7 steps each way, a stop button for each, and a channel switch for 1 to 4. It runs on 3 AAA batteries.

If wiring a battery box and motor is still new, start with the first motor build guide and the Motor Buggy, which the Floor Express lists as the build to do first.

Rule 1: channels decide who listens

Both the remote and the receiver have a channel switch. A receiver ignores every channel except its own, so the simplest way to stop two models fighting is to give them different channels. With four channels, four people can each drive their own model in the same room.

This is also the first thing to check when a model "won't respond". A switch knocked from 1 to 2 looks exactly like a flat battery.

Rule 2: the left dial is red, the right dial is blue

On one channel, the remote has two dials. The left dial drives the red socket of every receiver on that channel, and the right dial the blue socket. The RC Tank uses this to drive each track with its own motor, one on red and one on blue, so steering is two dials (tracks vs wheels covers how that skid steering works).

It also means one channel can run two trains: put one train's motor on red and the other's on blue, and each gets its own dial. The official help page for the original Power Functions trains says the same thing, which is how it gets up to eight trains running at once: two per channel, times four channels.

The Floor Express has its headlights on its receiver too, so on a shared channel one person's dial may switch on the other train's lights.

Rule 3: no light, no new command

The receiver listens for flashes of infrared light, invisible to us. Indoors that light bounces off walls and ceilings, so builders report it often still works from behind furniture. Under a blanket, it usually doesn't.

The surprise is what happens when the signal can't arrive. Train builders note that the receiver doesn't need a constant signal: it keeps doing what it was last told until a new command reaches it. One builder described exactly this: a train that went into a tunnel at speed and couldn't be stopped until it came out. The booklet's playtime idea is a blanket tunnel, so it is worth knowing before someone tries.

Predict it first

Two Floor Express trains, one remote. Choose the channels and sockets, decide whether a train is in a tunnel, then predict what each one does.

The booklet doesn't say which receiver socket takes the motor, so the lab lets you pick. It treats "can see the remote" as yes or no, which is simpler than real light.

Setting up a room

For a building club session or a train layout, this works well:

1. Give every model a channel. Write it on a sticker on both the model and its remote.
2. Share a channel on purpose only. Two trains on one channel should use different sockets, red for one and blue for the other.
3. Keep receivers in view. Keep each receiver's dome where its driver can see it. Tunnels are fine if they are short; slow or stop a train before it goes in, not inside.
4. Check channels first. When a model doesn't respond, check both channel switches, then the plugs, then the batteries.

For how the remote's signal becomes steering on a car, see how RC servo steering works, and the remote control idea page has a quick hand test for line of sight.