Snapshot

mattman gave you the answer in the second reply to your OP.

Unfortunately, what you've bought isn't NXT but the previous generation (RCX?) so you're going to be somewhat on your own with it. I'll see about starting a new thread after work today.

Ah, thanks. I didn't think to look under 'windscreen, decorated'. But no Bricklink shop in the EU has two.

It's quite easy. You need to make a convertor cable as described here then, assuming you're using the same motor design I referred to, using the NXT G motor block, 0.1 sec at 79% power in the direction you need does the job. A standard NXT brick can control up to three points but with a mux from the likes of Mindsensors you can connect as many as you need (cost permitting). Perhaps we should start a new thread for this?

It actually uses Lego's mini linear actuator but I agree it seems quite complex. There are self-contained LAs for NXT available from Firgelli but the smaller one is $50 and I can't see many of us going for that. I use this design for motorised points as it's reasonably compact and works well when NXT-controlled.

The design here does use a linear actuator plus the medium motor needed to drive it. There are self-contained items from Firgelli but they fail the cost test rather badly.

Where did you find the orange windscreen parts? I've done the red and black versions but would love an orange one.

8870 is the Lego light set that fits nicely into the 7939 loco. Here's mine, lit up: You'll see I've also changed the handrails and boosted the IR receiver by a full brick, changing the 'vents' at the sides to suit.

Unfortunately, this won't work - I just tried it to confirm my suspicions. The lights are controlled by the IR receiver so use the inner pair of wires, just like the motors. The AAA battery only supplies power on the outer pair, for use by the receiver. It does work with the LiPo battery but you have to use the built-in speed controller to provide power to the inner pair; just turning the battery on is not enough.

The lights are connected to the receiver, not the battery so will only come on when told to by the remote control.

In my opinion the only rational choice if you're starting from scratch is to use what's currently in production - PF/RC track and PF trains. 7939 is a good starter set as it includes a reasonable amount of track including a couple of switches (they most certainly do exist). You can buy a pack of 8 straights and 16 flexitracks (ugh!) or 2 switches and 4 curves from Lego or you can pick up extra straights, switches and curves on BL. Expect to pay around 1.8 euros per straight and a lot less for curves. Also note that the station and level crossing sets both include 4 sections of straight track.

I've sacrificed three long PF extensions. The light bley '9V' ends were spliced into short PF extensions to make 'Y' adapters for putting dual PF motors into loco's. The PF ends will be joined to the longest NXT cables to drive automated points.

Sounds like a fun project. Please keep us updated on how it goes. You should find you get at least three hours per charge so you would be able to run more-or-less continuously if you wanted to.

This seems just a little bit of overkill to me. One dual-engined loco should pull the six container wagons plus the other two locos without breaking into a sweat. If you're doing it just because you can then fair enough, enjoy yourself, but don't feel it's necessary for the number of units involved. My long(ish) red train is quite lively with just one dual-PF motor loco. I admit I've cheated by using five shared bogies which removes ten wheelsets and their attendant friction but the performance was very good indeed. A single PF motor in the loco had wheelspin with just six units. The only practical difficulty you're likely to have is keeping all the locos in sync. The pusher in particular is likely not to see the signal if the handset is aimed at the front pair. The IR signal is really quite feeble and the receivers tend to be swamped by ambient light so the range can be (is!) limited in open spaces. Jonathan

You can buy a suitable cable made by, I think, Firgelli or you can make your own using the instructions on World of Mindstorms (search for 'cables' and scroll down). If you want an IR link then you need a HiTechnic IRLink.

If only they were radio controlled! It's not radio, it's infra-red so is quite good indoors where the signal can bounce off the walls and ceiling but in open spaces like display halls the range of the remote control can be very limited. PF replaced RC as the infra-red control system. The problem with RC is that the receiver and battery box were built into the train bases so there was a limit on what you could build. PF uses a discrete 4x4x4 receiver and separate 4x8x4 battery box so they can be used in more than just trains. I agree completely about starting with 7939. The parts needed for the EN are just an XL motor, optional lights and an extra IR receiver and battery box as the hand control is in 7939.

No, you can't just replace it because there won't be any IR controller or battery to drive the PF motor. The OP want to keep 9V operation so it's a perfectly sensible question.Apart from the problems of actually fitting the PF motor in the 9V shell and the electrical connecions, I think the PF motor is designed to work with PWM so may not perform well with variable voltage.

A simple search here turns up this thread as the second entry on the Mallard. It's not full building instructions but intended to inspire you. The Emerald Night is supposedly based on the Flying Scotsman so is a good place to start. Mine has no smoke deflectors and two tenders to make it more like the Scotsman. I'd echo Mr Benn's suggestion about buying sooner rather than later. Jonathan

I've now put dual PF motors into a (red) 7939 loco and my 7938/7939 hybrid. I made a 'Y' extension cable for the former as it was just too tight squeezing in a reversing cable as well as lights. The latter had to be stretched by four studs to get the motors in and I just about squeezed the reversing switch in. At STEAM, it was pulling seven carriages and freight wagons plus a dummy loco on the back and was positively lively, hardly slowing at all for the corners.

Nice MOC! I've seen a similar problem when a friend tried to motorise a TS3 loco. It seemed to be something to do with friction in curves and removing the drive bands from one side fixed it. Jonathan

I agree with this approach - get the loco as good as possible without worrying about how to power it. Here's my green train at STEAM last weekend: Brick Express Large Prairie loco, pusher wagon, two coaches, two box cars, two open wagons and a guards van. I used an old 16-stud train base with motor cutout for the pusher wagon and it only needs four inverted slopes and two plates to attach the motor. Jonathan

More good news, Alban: I've not (yet!) been able to re-create the XP64 'large move' crash that I used to get so it looks like it may have been fixed by other work you've done. Jonathan

The file size is too small - it should be roughly 16MB - so it's not downloading completely.

Don't waste your time trying to repeatedly open a corrupt download. Delete it after the first failure and try the download again. I've just downloaded the file and it opened perfectly.

Please let me know when you've had the decency to remove the pop-up ads and I'll have another look.